Meiosis and Sexual Reproduction

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Meiosis and Sexual Reproduction
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Asexual Reproduction
Asexual
A Not
Sexual

• Called vegetative reproduction in plants
• A form of duplication using only mitosis.
• Example, a new plantgrows out of the root or a
  shoot from an existing plant.

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Asexual Reproduction

• Produces only genetically identical offspring
  since all divisions are by mitosis.
• Offspring called meaning that each is an exact
  copy of the original organism
• This method of reproduction is rapid and
  effective allowing the spread of an organism
• Example Bacterial growth
• Since the offspring are identical, there is no
  mechanism for introducing .

clones
diversity
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Asexual Reproduction

• In prokaryotes and some one-celled eukaryotes,
  cells undergo _____ _____
• Hydra reproduce by ________
• Planaria reproduce by ____________
• Several plants reproduce through vegetative
  reproduction.
• Most of these organisms can reproduce sexually as
  well.

binary fission
budding
fragmentation
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Why do organisms have sex if?
Sexual reproduction increases variety by
producing new genetic combinations.

• Its costly to the organism
• Its time-consuming
• There are far fewer offspring

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Sexual Reproduction

• Consists of Meiosis and Fertilization
• Meiosis Formation of two haploid sex cells
  (gametes).
• Meiosis is a process to convert a ________ cell
  to a ________ gamete, and cause a change in the
  genetic information to increase diversity in the
  offspring.
• In humans, meiosis only occurs in the ________
• Spermatogenesis In the ______(in males)
• Oogenesis In the _______ (in females)
• Fertilization Combination of genetic information
  from two separate cells that have one half the
  original genetic information

diploid
haploid
gonads
testes
ovaries
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Sexual Reproduction

• Gametes for fertilization usually come from
  separate parents
• Female produces an _____
• Male produces _______
• Both gametes are haploid, with a single set of
  _____________.
• The new individual is called a ______, with two
  sets of chromosomes (______).
• Once the zygote begins to divide, it is called an
  _______.

egg
sperm
chromosomes
zygote
diploid
embryo
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Chromosomes vary from species to species
one

• Prokaryotes generally have only ___ major
  chromosome
• Consisting of a single circle of DNA
• Turkeys have 82!
• Giant redwoods have 22!
• A tropical fish has the same number of
  chromosomes as humans, which is ____

46
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Chromosome Characteristics

• Diploid set for humans 2n 46
• Two types
• Autosomes (1 22)
• Sex Chromosomes (23)

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Chromosome Characteristics

• Autosomes
• Homologous chromosomes
• Humans have 22 sets of 2
• One from each parent
• Sex chromosomes
• Humans have 1 set of 2
• Female-sex chromosomes are homologous (XX)
• Male-sex chromosomes are non-homologous (XY)

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What can Chromosomes tell us?

• Scientists can organize chromosomes in a cell
  into a _________

karyotype
In a karyotype, chromosomes are arranged in order
of size, banding pattern, and centromere position
Lets see if we can arrange a karyotype together
http//learn.genetics.utah.edu/content/begin/trait
s/karyotype/
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What does this person pass on to the next
generation?
What sex will this person be?
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MeiosisReduction/Division

• Two divisions
• Meiosis I
• Meiosis II

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Prophase I

• Like Mitosis
• Nuclear membrane disappears
• Spindles form
• Chromatin condenses into chromatids

• Unlike Mitosis
• Homologous chromosomes group with other
  homologous chromosomes to form a tetrad
• A chiasma occurs at the point where the
  chromosomes cross over

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Metaphase I

1. Homologous chromosomes line up at the metaphase
   plate.
2. Microtubules (spindles) attach to the kinetochore

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Anaphase I

1. Homologous chromosomes separate.
2. Sister chromatids remain attached.

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Telophase I

• Two daughter cells are formed with each one
  containing only one chromosome of the homologous
  pair.
• The daughter cells are now haploid.

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Meiosis IIGamete formation
Prophase II

• DNA does not replicate.
• Prophase II is just like mitotic prophase.

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Metaphase II

• All of the chromosomes line up at the metaphase
  plate.

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Anaphase II

• Centromeres divide
• Sister chromatids migrate separately to each pole.

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Telophase II

• Cell division is complete.
• Four haploid daughter cells are obtained

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Summary of Meiosis
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