5. Cellular Reproduction and Genetics

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5. Cellular Reproduction and Genetics

• BJ Chapter 5 The Continuity of Life Part 1
  Advanced Genetics pp 153 - 179
• AP Module 7 Mendelian Genetics pp 196 - 226
• Reading Assignments
• Homework Assignment
• Lecture Topics

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5. Genetics BJ2 p 11

• Mechanism of Heredity BJ2 p112
• Genetics The study of heredity. Genetics (from
  Ancient Greek ?e?et???? genetikos, genitive and
  that from ???es?? genesis, origin), a
  discipline of biology, is the science of heredity
  and variation in living organisms. The fact that
  living things inherit traits from their parents
  has been used since prehistoric times to improve
  crop plants and animals through selective
  breeding. However, the modern science of
  genetics, which seeks to understand the process
  of inheritance, only began with the work of
  Gregor Mendel in the mid-nineteenth
  century.Although he did not know the physical
  basis for heredity, Mendel observed that
  organisms inherit traits via discrete units of
  inheritance, which are now called genes.
• The oldest a science Leviticus 1919Selective
  Breeding.
• Aristotle proposed the Particulate Theory theory
  that parts of the male and female join to
  reproduce.
• Preformationists I. The belief that there were
  tiny completely formed organisms in sperm that
  just grew up when planted in an egg.
• Gregor Mendel Performed experiments with garden
  peas, stated modern genetics.
• Proposed that there were pairs of factors in
  organisms and one of each pair goes to the
  offspring

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Genes

• Genes correspond to regions within DNA, a
  molecule composed of a chain of four different
  types of nucleotidesthe sequence of these
  nucleotides is the genetic information organisms
  inherit. DNA naturally occurs in a double
  stranded form, with nucleotides on each strand
  complementary to each other. Each strand can act
  as a template for creating a new partner
  strandthis is the physical method for making
  copies of genes that can be inherited.
• Genes are the section of DNA that produces a
  polypeptide chain of amino acids and causes
  trait.The DNA of one cell is roughly equal to
  1,000 600 page books.

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Gene
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Chromosomes

• Chromosomes Proteins that protect the strands of
  DNA and help in replication or transcription of
  RNA. They appear as a fuzzy tangled mass in the
  nucleus called Chromatin material. Different
  species have different numbers of chromosomes. A
  chromosome is an organized structure of DNA and
  protein that is found in cells. It is a single
  piece of coiled DNA containing many genes,
  regulatory elements and other nucleotide
  sequences. Chromosomes also contain DNA-bound
  proteins, which serve to package the DNA and
  control its functions. The word chromosome comes
  from the Greek ???µa (chroma, color) and s?µa
  (soma, body) due to their property of being very
  strongly stained by particular dyes. Chromosomes
  vary widely between different organisms. The DNA
  molecule may be circular or linear, and can be
  composed of 10,000 to 1,000,000,000 nucleotides
  in a long chain. Typically eukaryotic cells
  (cells with nuclei) have large linear chromosomes
  and prokaryotic cells (cells without defined
  nuclei) have smaller circular chromosomes,
  although there are many exceptions to this rule.
  Furthermore, cells may contain more than one type
  of chromosome for example, mitochondria in most
  eukaryotes and chloroplasts in plants have their
  own small chromosomes.

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Relationship between chromosomes DNA and genes

• Genes are relatively small sections of DNA which
  encode (provide a template for) proteins.
• Chromosomes are molecules that consist of a very
  long strand of DNA coiled many times, and a few
  proteins called histones which hold the whole
  structure together.
• To put things very simply, chromosomes are made
  up of genes and genes are made of DNA.
• One could use the analogy genes-words,
  chromosomes-books, genome-collective volume

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Chromosome Number

• There is a precise number of chromosomes typical
  for a given species. In any given asexually
  reproducing species, the chromosome number is
  always the same. In sexually reproducing
  organisms, the number of chromosomes in the body
  (somatic) cells is diploid (2n a pair of each
  chromosome), twice the haploid (1n) number found
  in the sex cells, or gametes. The haploid number
  is produced during meiosis. An organism with any
  multiple of the diploid number of chromosomes is
  said to be polyploid.
• Homologous chromosomes are chromosomes in a
  biological cell that pair (synapse) during
  meiosis. The pair are non-identical chromosomes
  that both contain information for the same
  biological features and contain the same genes at
  the same loci but possibly each have different
  alleles (that is, different genetic information)
  at those genes. For example, the two chromosomes
  may have genes encoding eye color, but one may
  code for brown eyes, the other for green.
• Non-homologous chromosomes representing all the
  biological features of an organism form a set,
  and the number of sets in a cell is called
  ploidy. In diploid organisms (most plants and
  animals), each member of a pair of homologous
  chromosomes is inherited from a different parent.
  But polyploid organisms have more than two
  homologous chromosomes.
• Homologous chromosomes are similar in length,
  except for sex chromosomes in several taxa, where
  the X chromosome is considerably larger than the
  Y chromosome. These chromosomes share only small
  regions of homology.
• Humans have 22 pairs of homologous non-sex
  chromosomes (called autosomes). Each member of a
  pair is inherited from one of their two parents.
  In addition, female humans have a homologous pair
  of sex chromosomes (2 X's) males have an X and a
  Y chromosome.
• Homologous chromosomes are two pairs of sister
  chromatids that have gone through the process of
  crossing over and meiosis. In this process the
  homologous chromosomes cross over (not the sister
  chromatids)each other and exchange genetic
  information. This causes each final cell of
  meiosis to have genetic information from both
  parents, a mechanism for genetic variation. The
  homologous chromosomes are similar in length.

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Mitosis

• When a cell divides into two identical cells.
  Mitosis is the process in which a eukaryotic cell
  separates the chromosomes in its cell nucleus
  into two identical sets in two daughter nuclei.
  It is generally followed immediately by
  cytokinesis, which divides the nuclei, cytoplasm,
  organelles and cell membrane into two daughter
  cells containing roughly equal shares of these
  cellular components. Mitosis and cytokinesis
  together define the mitotic (M) phase of the cell
  cycle - the division of the mother cell into two
  daughter cells, genetically identical to each
  other and to their parent cell. Mitosis divides
  the chromosomes in a cell nucleus.

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Mitosis
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Phases of Mitosis

• Interphase The time between cell divisions.The
  mitotic phase is a relatively short period of the
  cell cycle. It alternates with the much longer
  interphase, where the cell prepares itself for
  cell division. Interphase is therefore not part
  of mitosis. Interphase is divided into three
  phases, G1 (first gap), S (synthesis), and G2
  (second gap). During all three phases, the cell
  grows by producing proteins and cytoplasmic
  organelles. However, chromosomes are replicated
  only during the S phase. Thus, a cell grows (G1),
  continues to grow as it duplicates its
  chromosomes (S), grows more and prepares for
  mitosis (G2), and finally divides (M) before
  restarting the cycle..
• A centromere is a region of DNA typically found
  near the middle of a chromosome where two
  identical sister chromatids come in contact. It
  is involved in cell division as the point of
  mitotic spindle.
• Sister chromatids are identical copies of a
  chromosome connected by a centromere. Compare
  sister chromatids to homologous chromosomes,
  which are the two different copies of the same
  chromosome that diploid organisms (like humans)
  inherit, one from each parent. In other words,
  sister chromatids contain the same genes and same
  alleles, and homologous chromosomes contain the
  same genes but two copies of alleles, each of
  which might or might not be the same as each
  other. A full set of sister chromatids is created
  during the S subphase of interphase, when all the
  DNA in a cell is replicated. Identical chromosome
  pairs are separated into two different cells
  during mitosis, or cellular division. There is
  evidence that, in some species, sister chromatids
  are the preferred template for DNA repair. They
  are very strong, found within the cell during
  meiosis.
• Mother cell cell ready for mitosis.

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Preprophase

• Preprophase In plant cells only, prophase is
  preceded by a pre-prophase stage. In highly
  vacuolated plant cells, the nucleus has to
  migrate into the center of the cell before
  mitosis can begin. This is achieved through the
  formation of a phragmosome, a transverse sheet of
  cytoplasm that bisects the cell along the future
  plane of cell division. In addition to
  phragmosome formation, preprophase is
  characterized by the formation of a ring of
  microtubules and actin filaments (called
  preprophase band) underneath the plasma membrane
  around the equatorial plane of the future mitotic
  spindle. This band marks the position where the
  cell will eventually divide. The cells of higher
  plants (such as the flowering plants) lack
  centrioles with microtubules forming a spindle
  on the surface of the nucleus and then being
  organized into a spindle by the chromosomes
  themselves, after the nuclear membrane breaks
  down. The preprophase band disappears during
  nuclear envelope disassembly and spindle
  formation in prometaphase.

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Prophase

• Normally, the genetic material in the nucleus is
  in a loosely bundled coil called chromatin. At
  the onset of prophase, chromatin condenses
  together into a highly ordered structure called a
  chromosome. Since the genetic material has
  already been duplicated earlier in S phase, the
  replicated chromosomes have two sister
  chromatids, bound together at the centromere by
  the cohesion complex. Chromosomes are visible at
  high magnification through a light microscope.
• Close to the nucleus are structures called
  centrosomes, which are made of a pair of
  centrioles. The centrosome is the coordinating
  center for the cell's microtubules. A cell
  inherits a single centrosome at cell division,
  which replicates before a new mitosis begins,
  giving a pair of centrosomes. The two centrosomes
  nucleate microtubules (which may be thought of as
  cellular ropes or poles) to form the spindle by
  polymerizing soluble tubulin. Molecular motor
  proteins then push the centrosomes along these
  microtubules to opposite side of the cell.
  Although centrosomes help organize microtubule
  assembly, they are not essential for the
  formation of the spindle, since they are absent
  from plants, and centrosomes are not always used
  in meiosis.

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Prometaphase

• The nuclear envelope disassembles and
  microtubules invade the nuclear space. This is
  called open mitosis, and it occurs in most
  multicellular organisms. Fungi and some protists,
  such as algae or trichomonads, undergo a
  variation called closed mitosis where the spindle
  forms inside the nucleus or its microtubules are
  able to penetrate an intact nuclear envelope.
  Each chromosome forms two kinetochores at the
  centromere, one attached at each chromatid. A
  kinetochore is a complex protein structure that
  is analogous to a ring for the microtubule hook
  it is the point where microtubules attach
  themselves to the chromosome.Although the
  kinetochore structure and function are not fully
  understood, it is known that it contains some
  form of molecular motor. When a microtubule
  connects with the kinetochore, the motor
  activates, using energy from ATP to "crawl" up
  the tube toward the originating centrosome. This
  motor activity, coupled with polymerisation and
  depolymerisation of microtubules, provides the
  pulling force necessary to later separate the
  chromosome's two chromatids. When the spindle
  grows to sufficient length, kinetochore
  microtubules begin searching for kinetochores to
  attach to. A number of nonkinetochore
  microtubules find and interact with corresponding
  nonkinetochore microtubules from the opposite
  centrosome to form the mitotic spindle.
  Prometaphase is sometimes considered part of
  prophase.

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Metaphase

• A cell in late metaphase. All chromosomes (blue)
  but one have arrived at the metaphase plate. As
  microtubules find and attach to kinetochores in
  prometaphase, the centromeres of the chromosomes
  convene along the metaphase plate or equatorial
  plane, an imaginary line that is equidistant from
  the two centrosome poles.15 This even alignment
  is due to the counterbalance of the pulling
  powers generated by the opposing kinetochores,
  analogous to a tug-of-war between people of equal
  strength. In certain types of cells, chromosomes
  do not line up at the metaphase plate and instead
  move back and forth between the poles randomly,
  only roughly lining up along the midline.
  Metaphase comes from the Greek µeta meaning
  "after." Because proper chromosome separation
  requires that every kinetochore be attached to a
  bundle of microtubules (spindle fibres), it is
  thought that unattached kinetochores generate a
  signal to prevent premature progression to
  anaphase without all chromosomes being aligned.
  The signal creates the mitotic spindle checkpoint.

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Anaphase

• When every kinetochore is attached to a cluster
  of microtubules and the chromosomes have lined up
  along the metaphase plate, the cell proceeds to
  anaphase (from the Greek a?a meaning up,
  against, back, or re-). Two events then
  occur First, the proteins that bind sister
  chromatids together are cleaved, allowing them to
  separate. These sister chromatids, which have now
  become distinct sister chromosomes, are pulled
  apart by shortening kinetochore microtubules and
  move toward the respective centrosomes to which
  they are attached. Next, the nonkinetochore
  microtubules elongate, pushing the centrosomes
  (and the set of chromosomes to which they are
  attached) apart to opposite ends of the cell. The
  force that causes the centrosomes to move towards
  the ends of the cell is still unknown, although
  there is a theory that suggests that the rapid
  assembly and breakdown of microtubules may cause
  this movement.
• These two stages are sometimes called early and
  late anaphase. Early anaphase is usually defined
  as the separation of the sister chromatids, while
  late anaphase is the elongation of the
  microtubules and the microtubules being pulled
  farther apart. At the end of anaphase, the cell
  has succeeded in separating identical copies of
  the genetic material into two distinct
  populations.
• Daughter Chromosome Chromosome resulting from
  the separation of sister chromatids.

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Telophase

• (from the Greek te??? meaning "end") is a
  reversal of prophase and prometaphase events. It
  "cleans up" the after effects of mitosis. At
  telophase, the nonkinetochore microtubules
  continue to lengthen, elongating the cell even
  more. Corresponding sister chromosomes attach at
  opposite ends of the cell. A new nuclear
  envelope, using fragments of the parent cell's
  nuclear membrane, forms around each set of
  separated sister chromosomes. Both sets of
  chromosomes, now surrounded by new nuclei, unfold
  back into chromatin. Mitosis is complete, but
  cell division is not yet complete.

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Cytokinesis

• is often mistakenly thought to be the final part
  of telophase however, cytokinesis is a separate
  process that begins at the same time as
  telophase. Cytokinesis is technically not even a
  phase of mitosis, but rather a separate process,
  necessary for completing cell division. In animal
  cells, a cleavage furrow (pinch) containing a
  contractile ring develops where the metaphase
  plate used to be, pinching off the separated
  nuclei. In both animal and plant cells, cell
  division is also driven by vesicles derived from
  the Golgi apparatus, which move along
  microtubules to the middle of the cell. In plants
  this structure coalesces into a cell plate at the
  center of the phragmoplast and develops into a
  cell wall, separating the two nuclei. The
  phragmoplast is a microtubule structure typical
  for higher plants, whereas some green algae use a
  phycoplast microtubule array during cytokinesis.
  Each daughter cell has a complete copy of the
  genome of its parent cell. The end of cytokinesis
  marks the end of the M-phase.
• Daughter cellsThe cells that result from the
  reproductive division of one cell during mitosis
  or meiosis.

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Variation on Mitosis See Figure 5A3 BJ2 page 115

• Animal cell invaginate plant cells do not.
• Invagination means to fold or pinch-in inward or
  to sheath.
• Plant cells form division plat.
• Some unicellular organism- all phases occur
  within the nuclear membrane.
• Variation in time form 10 min to 3 hours
• Continuous - such as skin
• Limited - divides for a certain period of time
  then stops - such as nerve cells

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Meiosis
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Plant Meiosis
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Uses of Mitosis

• Growth, repair and replacemen of cells in
  multicell organisms
• Asexual reproduction
• Fragmentation
• Budding
• Spore

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Clone and Cloning

• Cloning in biology is the process of producing
  populations of genetically-identical individuals
  that occurs in nature when organisms such as
  bacteria, insects or plants reproduce asexually.
  Organism cloning refers to the procedure of
  creating a new multicellular organism,
  genetically identical to another. Cloning in
  biotechnology refers to processes used to create
  copies of DNA fragments (molecular cloning),
  cells (cell cloning), or organisms.
• Natural Clones Identical twins are natural
  clones. Organism cloning is an natural an asexual
  method of reproduction, where fertilization or
  inter-gamete contact does not take place. Asexual
  reproduction is a naturally occurring phenomenon
  in many species, including most plants and some
  insects.
• Artificial Clones Artificial cloning is
  controversial subject. Artificial clones for
  simple organisms such as sponges and jelly fish
  from embryo cells starting in 1894. Some simple s
  but adult mammals weren't cloned until 1996. Farm
  animals have been cloned by the hundreds
  recently, and companies want to use them in food
  production. Mammal cloning milestones
• 1996 Dolly the sheep (made public in 1997)
• 1998 Mice, cattle
• 1999 Goats
• 2000 Pigs cloned using mice, clones of clones
  are produced
• 2002 Rabbits, cats
• 2003 Horses, rats
• 2005 Dog
• Human Clones Natural human clones exist as
  identical twins. In 2004 adult human cells were
  cloned to create embryos, which are destroyed to
  extract cells for research. This is very
  controversial as many Christians view that every
  embryo is fully human.

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Meiosis

• (See figure 5A-7 Meiosis in Animal Cells)
• In biology, meiosis (pronounced /ma?'o?s?s/) is a
  process of reductional division in which the
  number of chromosomes per cell is halved. In
  animals, meiosis always results in the formation
  of gametes, while in other organisms it can give
  rise to spores. As with mitosis, before meiosis
  begins, the DNA in the original cell is
  replicated during S-phase of the cell cycle. Two
  cell divisions separate the replicated
  chromosomes into four haploid gametes or spores.

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• Meiosis is essential for sexual reproduction and
  therefore occurs in all eukaryotes (including
  single-celled organisms) that reproduce sexually.
  A few eukaryotes, notably the Bdelloid rotifers,
  have lost the ability to carry out meiosis and
  have acquired the ability to reproduce by
  parthenogenesis. Meiosis does not occur in
  archaea or bacteria, which reproduce via asexual
  processes such as binary fission.
• During meiosis, the genome of a diploid germ
  cell, which is composed of long segments of DNA
  packaged into chromosomes, undergoes DNA
  replication followed by two rounds of division,
  resulting in four haploid cells. Each of these
  cells contain one complete set of chromosomes, or
  half of the genetic content of the original cell.
  If meiosis produces gametes, these cells must
  fuse during fertilization to create a new diploid
  cell, or zygote before any new growth can occur.
  Thus, the division mechanism of meiosis is a
  reciprocal process to the joining of two genomes
  that occurs at fertilization. Because the
  chromosomes of each parent undergo homologous
  recombination during meiosis, each gamete, and
  thus each zygote, will have a unique genetic
  blueprint encoded in its DNA. Together, meiosis
  and fertilization constitute sexuality in the
  eukaryotes, and generate genetically distinct
  individuals in populations.

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• In all plants, and in many protists, meiosis
  results in the formation of haploid cells that
  can divide vegetatively without undergoing
  fertilization, referred to as spores. In these
  groups, gametes are produced by mitosis.
• Meiosis uses many of the same biochemical
  mechanisms employed during mitosis to accomplish
  the redistribution of chromosomes. There are
  several features unique to meiosis, most
  importantly the pairing and recombination between
  homologous chromosomes.
• Meiosis comes from the root -meio, meaning less.

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• Because meiosis is a "one-way" process, it cannot
  be said to engage in a cell cycle as mitosis
  does. However, the preparatory steps that lead up
  to meiosis are identical in pattern and name to
  the interphase of the mitotic cell cycle.

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• Interphase is divided into three phases
• Growth 1 (G1) phase This is a very active
  period, where the cell synthesizes its vast array
  of proteins, including the enzymes and structural
  proteins it will need for growth. In G1 stage
  each of the chromosomes consists of a single
  (very long) molecule of DNA. In humans, at this
  point cells are 46 chromosomes, 2N, identical to
  somatic cells.
• Synthesis (S) phase The genetic material is
  replicated each of its chromosomes duplicates,
  producing 46 chromosomes each made up of two
  sister chromatids. The cell is still considered
  diploid because it still contains the same number
  of centromeres. The identical sister chromatids
  have not yet condensed into the densely packaged
  chromosomes visible with the light microscope.
  This will take place during prophase I in
  meiosis.
• Growth 2 (G2) phase G2 phase is absent in
  Meiosis

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• Interphase is followed by meiosis I and then
  meiosis II. Meiosis I consists of separating the
  pairs of homologous chromosome, each made up of
  two sister chromatids, into two cells. One entire
  haploid content of chromosomes is contained in
  each of the resulting daughter cells the first
  meiotic division therefore reduces the ploidy of
  the original cell by a factor of 2.

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• Meiosis II consists of decoupling each
  chromosome's sister strands (chromatids), and
  segregating the individual chromatids into
  haploid daughter cells. The two cells resulting
  from meiosis I divide during meiosis II, creating
  4 haploid daughter cells. Meiosis I and II are
  each divided into prophase, metaphase, anaphase,
  and telophase stages, similar in purpose to their
  analogous subphases in the mitotic cell cycle.
  Therefore, meiosis includes the stages of meiosis
  I (prophase I, metaphase I, anaphase I, telophase
  I), and meiosis II (prophase II, metaphase II,
  anaphase II, telophase II).
• Meiosis generates genetic diversity in two ways
  (1) independent alignment and subsequent
  separation of homologous chromosome pairs during
  the first meiotic division allows a random and
  independent selection of each chromosome
  segregates into each gamete and (2) physical
  exchange of homologous chromosomal regions by
  recombination during prophase I results in new
  combinations of DNA within chromosomes.
• A diagram of the meiotic phases

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Meiosis-phases Meiosis I

• Meiosis I separates homologous chromosomes,
  producing two haploid cells (23 chromosomes, N in
  humans), so meiosis I is referred to as a
  reductional division. A regular diploid human
  cell contains 46 chromosomes and is considered 2N
  because it contains 23 pairs of homologous
  chromosomes. However, after meiosis I, although
  the cell contains 46 chromatids it is only
  considered as being N, with 23 chromosomes,
  because later in anaphase I the sister chromatids
  will remain together as the spindle pulls the
  pair toward the pole of the new cell. In meiosis
  II, an equational division similar to mitosis
  will occur whereby the sister chromatids are
  finally split, creating a total of 4 haploid
  cells (23 chromosomes, N) per daughter cell from
  the first division.

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Prophase I

• During prophase I, DNA is exchanged between
  homologous chromosomes in a process called
  homologous recombination. This often results in
  chromosomal crossover. The new combinations of
  DNA created during crossover are a significant
  source of genetic variation, and may result in
  beneficial new combinations of alleles. The
  paired and replicated chromosomes are called
  bivalents or tetrads, which have two chromosomes
  and four chromatids, with one chromosome coming
  from each parent. At this stage, non-sister
  chromatids may cross-over at points called
  chiasmata (plural singular chiasma).

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Leptotene

• The first stage of prophase I is the leptotene
  stage, also known as leptonema, from Greek words
  meaning "thin threads".1 During this stage,
  individual chromosomes begin to condense into
  long strands within the nucleus. However the two
  sister chromatids are still so tightly bound that
  they are indistinguishable from one another.

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Zygotene

• The zygotene stage, also known as zygonema, from
  Greek words meaning "paired threads",1 occurs
  as the chromosomes approximately line up with
  each other into homologous chromosomes. This is
  called the bouquet stage because of the way the
  telomeres cluster at one end of the nucleus.

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Pachytene

• The pachytene stage, also known as pachynema,
  from Greek words meaning "thick threads",1
  contains the following chromosomal crossover.
  Nonsister chromatids of homologous chromosomes
  randomly exchange segments of genetic information
  over regions of homology. (Sex chromosomes,
  however, are not wholly identical, and only
  exchange information over a small region of
  homology.) Exchange takes place at sites where
  recombination nodules (the aforementioned
  chiasmata) have formed. The exchange of
  information between the non-sister chromatids
  results in a recombination of information each
  chromosome has the complete set of information it
  had before, and there are no gaps formed as a
  result of the process. Because the chromosomes
  cannot be distinguished in the synaptonemal
  complex, the actual act of crossing over is not
  perceivable through the microscope.

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Diplotene

• During the diplotene stage, also known as
  diplonema, from Greek words meaning "two
  threads", the synaptonemal complex degrades and
  homologous chromosomes separate from one another
  a little. The chromosomes themselves uncoil a
  bit, allowing some transcription of DNA. However,
  the homologous chromosomes of each bivalent
  remain tightly bound at chiasmata, the regions
  where crossing-over occurred. The chiasmata
  remain on the chromosomes until they are severed
  in Anaphase I.
• In human fetal oogenesis all developing oocytes
  develop to this stage and stop before birth. This
  suspended state is referred to as the dictyotene
  stage and remains so until puberty. In males,
  only spermatogonia(Spermatogenesis) exist until
  meiosis begins at puberty.
• (See Figure 5A-8 BJ2 p 122for diagram of
  Spermatogenesis.)

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Diakinesis

• Chromosomes condense further during the
  diakinesis stage, from Greek words meaning
  "moving through". This is the first point in
  meiosis where the four parts of the tetrads are
  actually visible. Sites of crossing over entangle
  together, effectively overlapping, making
  chiasmata clearly visible. Other than this
  observation, the rest of the stage closely
  resembles prometaphase of mitosis the nucleoli
  disappear, the nuclear membrane disintegrates
  into vesicles, and the meiotic spindle begins to
  form.

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Synchronous processes

• During these stages, two centrosomes, containing
  a pair of centrioles in animal cells, migrate to
  the two poles of the cell. These centrosomes,
  which were duplicated during S-phase, function as
  microtubule organizing centers nucleating
  microtubules, which are essentially cellular
  ropes and poles. The microtubules invade the
  nuclear region after the nuclear envelope
  disintegrates, attaching to the chromosomes at
  the kinetochore. The kinetochore functions as a
  motor, pulling the chromosome along the attached
  microtubule toward the originating centriole,
  like a train on a track. There are four
  kinetochores on each tetrad, but the pair of
  kinetochores on each sister chromatid fuses and
  functions as a unit during meiosis I.
• Microtubules that attach to the kinetochores are
  known as kinetochore microtubules. Other
  microtubules will interact with microtubules from
  the opposite centriole these are called
  nonkinetochore microtubules or polar
  microtubules. A third type of microtubules, the
  aster microtubules, radiates from the centrosome
  into the cytoplasm or contacts components of the
  membrane skeleton.

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Metaphase I

• Homologous pairs move together along the
  metaphase plate As kinetochore microtubules from
  both centrioles attach to their respective
  kinetochores, the homologous chromosomes align
  along an equatorial plane that bisects the
  spindle, due to continuous counterbalancing
  forces exerted on the bivalents by the
  microtubules emanating from the two kinetochores
  of homologous chromosomes. The physical basis of
  the independent assortment of chromosomes is the
  random orientation of each bivalent along the
  metaphase plate, with respect to the orientation
  of the other bivalents along the same equatorial
  line.

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Anaphase I

• Kinetochore microtubules shorten, severing the
  recombination nodules and pulling homologous
  chromosomes apart. Since each chromosome has only
  one functional unit of a pair of kinetochores,
  whole chromosomes are pulled toward opposing
  poles, forming two haploid sets. Each chromosome
  still contains a pair of sister chromatids.
  Nonkinetochore microtubules lengthen, pushing the
  centrioles farther apart. The cell elongates in
  preparation for division down the center.

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Telophase I

• The last meiotic division effectively ends when
  the chromosomes arrive at the poles. Each
  daughter cell now has half the number of
  chromosomes but each chromosome consists of a
  pair of chromatids. The microtubules that make up
  the spindle network disappear, and a new nuclear
  membrane surrounds each haploid set. The
  chromosomes uncoil back into chromatin.
  Cytokinesis, the pinching of the cell membrane in
  animal cells or the formation of the cell wall in
  plant cells, occurs, completing the creation of
  two daughter cells. Sister chromatids remain
  attached during telophase I.
• Cells may enter a period of rest known as
  interkinesis or interphase II. No DNA replication
  occurs during this stage.

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Meiosis II

• Meiosis II is the second part of the meiotic
  process. Much of the process is similar to
  mitosis. The end result is production of four
  haploid cells (23 chromosomes, 1N in humans) from
  the two haploid cells (23 chromosomes, 1N each
  of the chromosomes consisting of two sister
  chromatids) produced in meiosis I. The four main
  steps of Meiosis II are Prophase II, Metaphase
  II, Anaphase II, and Telophase II.

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Prophase II

• Prophase II takes an inversely proportional time
  compared to telophase I. In this prophase we see
  the disappearance of the nucleoli and the nuclear
  envelope again as well as the shortening and
  thickening of the chromatids. Centrioles move to
  the polar regions and arrange spindle fibers for
  the second meiotic division.

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metaphase II

• In metaphase II, the centromeres contain two
  kinetochores that attach to spindle fibers from
  the centrosomes (centrioles) at each pole. The
  new equatorial metaphase plate is rotated by 90
  degrees when compared to meiosis I, perpendicular
  to the previous plate.

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anaphase II

• This is followed by anaphase II, where the
  centromeres are cleaved, allowing microtubules
  attached to the kinetochores to pull the sister
  chromatids apart. The sister chromatids by
  convention are now called sister chromosomes as
  they move toward opposing poles.

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telophase II

• The process ends with telophase II, which is
  similar to telophase I, and is marked by
  uncoiling and lengthening of the chromosomes and
  the disappearance of the spindle. Nuclear
  envelopes reform and cleavage or cell wall
  formation eventually produces a total of four
  daughter cells, each with a haploid set of
  chromosomes. Meiosis is now complete and ends up
  with four new daughter cells.

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Gametes

• A gamete (from Ancient Greek ?aµ?t?? translated
  gamete wife, gametes husband) is a cell that
  fuses with another gamete during fertilization
  (conception) in organisms that reproduce
  sexually. In species that produce two
  morphologically distinct types of gametes, and in
  which each individual produces only one type, a
  female is any individual that produces the larger
  type of gamete called an ovum (or egg) and a
  male produces the smaller tadpole-like type
  called a sperm. This is an example of anisogamy
  or heterogamy, the condition wherein females and
  males produce gametes of different sizes (this is
  the case in humans the human ovum is
  approximately 20 times larger than the human
  sperm cell). In contrast, isogamy is the state of
  gametes from both sexes being the same size and
  shape, and given arbitrary designators for mating
  type. The name gamete was introduced by the
  Austrian biologist Gregor Mendel. Gametes carry
  half the genetic information of an individual,
  one chromosome of each type. In humans, an ovum
  can carry only X chromosome (of the X and Y
  chromosomes), whereas a sperm can carry either an
  X or a Y hence, it has been suggested that males
  have the control of the sex of any resulting
  zygote, as the genotype of the sex-determining
  chromosomes of a male must be XY and a female XX.
  In other words, due to the presence of the Y
  chromosome exclusively in the sperm, it is that
  gamete alone that can determine that an offspring
  will be a male.

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• Spermatogenesis is the process by which male
  spermatogonia develop into mature spermatozoa.
  Spermatozoa are the mature male gametes in many
  sexually reproducing organisms. Thus,
  spermatogenesis is the male version of
  gametogenesis. In mammals it occurs in the male
  testes and epididymis in a stepwise fashion, and
  for humans takes approximately 64 days.1
  Spermatogenesis is highly dependent upon optimal
  conditions for the process to occur correctly,
  and is essential for sexual reproduction. It
  starts at puberty and usually continues
  uninterrupted until death, although a slight
  decrease can be discerned in the quantity of
  produced sperm with increase in age. The entire
  process can be broken up into several distinct
  stages, each corresponding to a particular type
  of cell.
• See Figure 5A-8 BJ2 p 122for diagram of
  Spermatogenesis.)

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• Oogenesis is the creation of an ovum (egg cell).
  It is the female process of gametogenesis. It
  involves the various stages of immature ova.
• Plant Meiosis Somewhat different than animal
  meiosis. Cytokinesis is very different. Pollen
  contain the male haploid cells. Pollen retains a
  large amount of cytoplasm, so a source of food
  for many insects. Only one of the haploid cells
  forms the zygote. Ovum of plant contains several
  haploid nuclie because cytokinesis in plants does
  not occur after the ovum nucleus has been formed.
  
• Parthenogenesis means the growth and development
  of an embryo or seed without fertilization by a
  male. Parthenogenesis occurs naturally in some
  lower plants (called agamospermy), invertebrates
  (e.g. water fleas, aphids) and some vertebrates
  (e.g. lizards, salamanders, some fish, and even
  turkeys). Parthenogenetic populations are
  typically all-female. As with all types of
  asexual reproduction, there are both costs and
  benefits associated with parthenogenesis.
• The alteration between parthenogenesis and sexual
  reproduction is called heterogamy. Forms of
  reproduction related to parthenogenesis but that
  require the presence of sperm are known as
  gynogenesis and hybridogenesis.

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Sexual Reproduction

• Sexual Reproduction Sexual reproduction is
  characterized by processes that pass a
  combination of genetic material to offspring,
  resulting in diversity. The main two processes
  are meiosis, involving the halving of the number
  of chromosomes and fertilization, involving the
  fusion of two gametes and the restoration of the
  original number of chromosomes. During meiosis,
  the chromosomes of each pair usually cross over
  to achieve genetic recombination. Sexual
  reproduction is the primary method of
  reproduction for the vast majority of macroscopic
  organisms, including almost all animals and
  plants. Evolutionary theory has now explanation
  for why sexual reproduction exits.

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Sexual Reproduction
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Basic Genetics (BJ2 p125)

• Mendel Genetics
• Mendel Did his work at the University of Vienna
  in 1850's and 1860's.
• Mendel discovered that by crossing white flower
  and purple flower plants, the result was not a
  hybrid offspring. Rather than being a mix of the
  two, the offspring was purple flowered. He then
  conceived the idea of heredity units, which he
  called "factors", one which is a recessive
  characteristic and the other dominant. Mendel
  said that factors, later called genes, normally
  occur in pairs in ordinary body cells, yet
  segregate during the formation of sex cells. Each
  member of the pair becomes part of the separate
  sex cell.

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Mendel's Concepts

• Concept of unit characteristics
• A unit of characteristic is a biological entity
  (factor) we now call genes that come in pairs.
• Concept of Dominant and Recessive
• The dominant gene, such as the purple flower in
  Mendel's plants, will hide the recessive gene,
  the white flower. After Mendel self-fertilized
  the F1 generation and obtained the 31 ratio, he
  correctly theorized that genes can be paired in
  three different ways for each trait AA, aa, and
  Aa. The capital A represents the dominant factor
  and lowercase a represents the recessive. (The
  last combination listed above, Aa, will occur
  roughly twice as often as each of the other two,
  as it can be made in two different ways, Aa or
  aA.)
• Mendel stated that each individual has two
  factors for each trait, one from each parent. The
  two factors may or may not contain the same
  information. If the two factors are identical,
  the individual is called homozygous for the
  trait. If the two factors have different
  information, the individual is called
  heterozygous. The alternative forms of a factor
  are called alleles. The genotype of an individual
  is made up of the many alleles it possesses. An
  individual's physical appearance, or phenotype,
  is determined by its alleles as well as by its
  environment. An individual possesses two alleles
  for each trait one allele is given by the female
  parent and the other by the male parent. They are
  passed on when an individual matures and produces
  gametes egg and sperm. When gametes form, the
  paired alleles separate randomly so that each
  gamete receives a copy of one of the two alleles.
  The presence of an allele doesn't promise that
  the trait will be expressed in the individual
  that possesses it. In heterozygous individuals
  the only allele that is expressed is the
  dominant. The recessive allele is present but its
  expression is hidden.

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Concept or Law of Segregation (The "First Law")

• The Law of Segregation states that when any
  individual produces gametes, the copies of a gene
  separate, so that each gamete receives only one
  copy. A gamete will receive one allele or the
  other. The direct proof of this was later found
  when the process of meiosis came to be known. In
  meiosis the paternal and maternal chromosomes get
  separated and the alleles with the characters are
  segregated into two different gametes.

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Concept or Law of Independent Assortment (The
"Second Law")

• The Law of Independent Assortment, also known as
  "Inheritance Law", states that alleles of
  different genes assort independently of one
  another during gamete formation. While Mendel's
  experiments with mixing one trait always resulted
  in a 31 ratio between dominant and recessive
  phenotypes, his experiments with mixing two
  traits (dihybrid cross) showed 9331 ratios But
  the 9331 table shows that each of the two
  genes are independently inherited with a 31
  ratio. Mendel concluded that different traits is
  inherited independently of each other, so that
  there is no relation, for example, between a
  cat's color and tail length. This is actually
  only true for genes that are not linked to each
  other.

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Terms

• Self Pollination Self-pollination is a form of
  pollination that can occur when a flower has both
  stamen and a carpel in which the cultivar or
  species is self fertile and the stamens and the
  sticky stigma of the carpel contact each other to
  accomplish pollination. The term is inaccurately
  used in many cases where an outside pollinator is
  actually required such plants are merely self
  fertile, or self pollenizing. Few plants actually
  self pollinate. The mechanism is seen most often
  in some legumes such as peanuts. In another
  legume, Soybeans, the flowers open and remain
  receptive to insect cross pollination during the
  day if this is not accomplished, the flowers
  self pollinate as they are closing.
• Cross Pollination The transfer of pollen from
  the anther (The pollen-bearing part of the
  stamen) of the flower of one plant to the flowers
  of a different plant.
• Offspring (Filial generations) F1, F2 etc.
  Offspring generation. F1 is the first offspring
  or filial generation F2 is the second and so
  on. Successive generations of progeny in a
  controlled series of crosses, starting with two
  specific parents (the P generation) and selfing
  or intercrossing the progeny of each new (F1 F2
  . . . ) generation.

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Terms Cont'd

• Genotype The actual genes you posses such as aa,
  Aa, AA
• Phenotype Physical expression of your genes.
  Example Aa and AA have same phenotype.
• Allele Either of a pair (or series) of
  alternative forms of a gene that can occupy the
  same locus on a particular chromosome and that
  control a certain characteristics. A, a
• Homozygous Having identical alleles at
  corresponding chromosomal loci, AA, aa
• Heterozygous Having dissimilar alleles at
  corresponding chromosomal loci, Aa
• Monohybrid A hybrid produced by crossing parents
  that are homozygous except for a single gene
  locus that has 1 set of alleles (two alleles).

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See Fig. 5B-3 p 127
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Punnett Squares

• The Punnett square is a diagram that is used to
  predict the outcome of a particular cross or
  breeding experiment. It is named after Reginald
  C. Punnett, who devised the approach, and is used
  by biologists to determine the probability of an
  offspring having a particular genotype. The
  Punnett square is a summary of every possible
  combination of one maternal allele with one
  paternal allele for each gene being studied in
  the cross.

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Genetic Ratios

• AA Aa aa
• You can predict the genetic and phenotype ratios
  using a Punnett square
• You can also figure the dominate or recessiveness
  of a plan, using a test cross and applying the
  receive and dominate rules with a Punnett Square.

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Multiple Alleles

• Any of a set of three or more alleles, or
  alternative states of a gene, only two of which
  can be present in a diploid organism.
• Example color r, w, y, so you can have more
  phenotypes.

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Multiple Alleles - Blood Type
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Dihybrid Cross (See BJ2 Fig 5B-8 p 134)

• A dihybrid cross is a cross between F1 offspring
  (first generation offspring) of two individuals
  that differ in two traits of particular interest.
  For example RRyy/rrYY or RRYY/rryy parents
  result in F1 offspring that are heterozygous for
  both R Y.
• A dihybrid cross is often used to test for
  dominant and recessive genes in two separate
  characteristics. Such a cross has a variety of
  uses in Mendelian genetics.
• Meiosis is the cellular process of gamete
  creation, it is where sperm and eggs get the
  unique set of genetic information that will be
  used in the development and growth of the
  offspring of the mating. The rules of meiosis as
  they apply to the dihybrid are codified in
  Mendel's First Law and Mendel's Second Law also
  called the Law of Segregation and the Law of
  Independent Assortment.
• For genes on separate chromosomes each allele
  pair shows independent segregation. If the first
  filial generation (F1 generation) produces four
  offspring, the second filial generation, which
  occurs by crossing the members of the first
  filial generation, shows a phenotypic
  (appearance) ratio of 9331.

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Mendel's Law of Independent Assortment Multiple -
Gene Interaction

• Mendel's Law of Independent Assortment
• The Law of Independent Assortment, also known as
  "Inheritance Law", states that alleles of
  different genes assort independently of one
  another during gamete formation. While Mendel's
  experiments with mixing one trait always resulted
  in a 31 ratio between dominant and recessive
  phenotypes, his experiments with mixing two
  traits (dihybrid cross) showed 9331 ratios But
  the 9331 table shows that each of the two
  genes are independently inherited with a 31
  ratio. Mendel concluded that different traits is
  inherited independently of each other, so that
  there is no relation, for example, between a
  cat's color and tail length. This is actually
  only true for genes that are not linked to each
  other.
• Multiple Gene Interaction Occurs When Genes at
  Multiple Loci Determine a Single Phenotype In
  dihybrid crosses

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Sex Determined and Sex Linked Traits

• Sex Chromosomes X and Y chromosomes are the sex
  determining chromosomes.
• In people and mammals the XX is female XY is male
  there is no YY
• In birds, the opposite is true the male is the
  homogametic sex, having two X chromosomes (XX),
  and the female (hen) is heterogametic, having one
  X and one Y chromosome (XY).
• Punnett square shows that there is a 50 50 chance
  for a male or female to be born.
• Sex of human baby and mammals determined by the
  father
• Sex of birds determined by mother
• Sex Determined Traits Trait only associated with
  one sex or the other, not both.
• Sex-linked Traits Sex linkage is the phenotypic
  expression of an allele that is related to the
  chromosomal sex of the individual. This mode of
  inheritance is in contrast to the inheritance of
  traits on autosomal chromosomes, where both sexes
  have the same probability of expressing the
  trait. Since, in humans, there are many more
  genes on the X than there are on the Y, there are
  many more X-linked traits than there are Y-linked
  traits. For some alleles (X nad Y) males only
  have one and females two. Think of the Y as
  missing one branch of the "X"
• Examples Color blindness and hemophilia (see BJ2
  Fig 5B-2 p 140)
• Carriers Sex linkage is the phenotypic
  expression of an allele that is related to the
  chromosomal sex of the individual. This mode of
  inheritance is in contrast to the inheritance of
  traits on autosomal chromosomes, where both sexes
  have the same probability of expressing the
  trait. Since, in humans, there are many more
  genes on the X than there are on the Y, there are
  many more X-linked traits than there are Y-linked
  traits.

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Sex Linked Possiblities