Bio 1010

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Bio 1010
Dr. Bonnie A. Bain
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CHAPTER 8 Cell
Reproduction Part 2
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Assignments See handout 10 points
each Complete 4 of these by the end of the
semester APA format Standard citation format
used in science writing
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Assignments APA format examples Author.
Year. Title. Journal name, volume,
pages Karcher, C. A. (1986). Censorship,
American style The case of Lydia Maria Child.
Studies in the American Renaissance, 9, 283-303.
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MITOSIS SIMPLE CELL DIVISION Cells make exact
replicas of themselves, including chromosome
number MEIOSIS NOT-SO-SIMPLE CELL DIVISION
Function forms gametes (egg, sperm) Meiosis
involves both nuclear and cellular division and
is more complicated than mitosis
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Unnumbered Figure 08_UN141c
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Why Meiosis?? 1. Allows Maple trees to make
more maple trees Goldfish to make more
goldfish Humans to make more humans etc. When
sperm and egg combine, the new individual is not
an exact copy of either parent
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Figure 8.12
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Why Meiosis?? 2. Meiosis maintains the constancy
of the chromosome number for a species Any
deviation from this number can result in a
pathological condition Example Down's Syndrome
(Trisomy 21)
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Figure 8.22
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Chromosomes Humans 23 pairs of homologous
chromosomes or 46 individual ones Since sperm
and egg are going to combine at fertilization,
each needs half the chromosome number so that
the zygote will have the normal number of
chromosomes (23 pairs)
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Some Definitions Somatic cell all cells
except the germ cells Germ cell Cells which
make gametes (eggs or sperm)
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Some More Definitions Karyotype A picture of
all chromosomes in a cell Taken during
Metaphase Homologous chromosomes Chromosomes
occur in pairs One is from Mom and one is from
Dad
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Figure 8.13
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Homologous chromosomes Each carry versions of
the same gene Example an eye color gene The
chromosome from Mom has the gene for blue
eyes The chromosome from Dad has the gene for
brown eyes
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At Metaphase, the homologous pairs
of chromosomes line up on the spindle
fibers Humans have 23 pairs of chromosomes 22
of these are called autosomes Pair 23 are the
sex chromosomes (next slide)
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SEX CHROMOSOMES Females have an identical pair
of these XX Males have one X and one little
tiny Y XY
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Figure 8.13
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Extra Photo 08.13x4
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Extra Photo 08.13x2
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More definitions 2n Diploid number (normal
number) n Haploid number (half the normal
number) 4n, 6n, 8n, etc. Polyploid Plants are
OK with this, animals not so OK
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In humans 2n 23 pairs of chromosomes (46
total) n 23 individual chromosomes ALL BODY
CELLS EXCEPT GAMETES ARE DIPLOID GAMETES ARE
HAPLOID
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Figure 8.14
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Question How can we produce large quantities
of gametes which will have only half the normal
chromosome number? Answer through Meiosis
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Eggs are produced in the female ovaries Sperm
are produced in the male testes Fertilization
egg and sperm join together Zygote the
developing embryo
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Figure 8.14
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COMPARISON OF MITOSIS AND MEIOSIS Mitosis The
chromosomes replicate once and The nucleus
divides once and the cytoplasm divides
once Result 2 new daughter cells with the same
chromosome number (2n or diploid)
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Unnumbered Figure 08_UN141c
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COMPARISON OF MITOSIS AND MEIOSIS Meiosis Chromo
somes replicate once and the nucleus divides
twice (cytoplasm also divides several
times) Result 4 new daughter cells, each has
half the normal chromosome number or n (haploid)
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Figure 8.15
One pair (red, blue) of homologous chromosomes
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Meiosis I Prophase I Metaphase I Anaphase
I Telophase I End Result 2 haploid
cells Meiosis II Prophase II Metaphase
II Anaphase II Telophase II End Result 4
haploid cells
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Meiosis I Prophase I Chromatin condenses to form
chromosomes Each chromosome made of 2 chromatids
joined by centromere Homologous chromosomes
form pairs (tetrads) Crossing over occurs here
Centrioles produce spindle fibers Nuclear
envelope disintegrates
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Meiosis I
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Meiosis I Metaphase I Tetrads line up on
equatorial plate of cell Their centromeres are
attached to the spindle fibers Anaphase I
Homologous chromosomes pull apart and migrate to
opposite poles Telophase I New nuclear envelopes
form around the chromosomes Cytokinesis
(cytoplasmic division) occurs Result 2 haploid
cells
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Meiosis I
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Meiosis II Prophase II Each chromosome has 2
chromatids New mitotic spindle forms Nuclear
envelopes disintegrate again Metaphase
II Chromosomes align on equatorial plane (again)
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Meiosis II
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Meiosis II Anaphase II Centromeres
divide Sister chromatids migrate to opposite
poles Each chromatid is now a single strand (no
longer double)
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Meiosis II
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Meiosis II Telophase II New nuclear envelopes
form Chromosomes unwind and disappear Cytoplas
m divides again End Result 4 haploid cells
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Spermatogenesis
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Oogenesis
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Origins of Genetic Variation Independent
Assortment of Chromosomes Which chromosomes go
into each gamete is a random process (see next
slide) Crossing Over Chromosomes have sticky
ends When they are lined up, the ends stick to
each other and sometimes switch places
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Figure 8.18
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Figure 8.19
Crossing Over Chiasma the place where crossing
over occurs Recombinant Chromosomes These are
the result of the genetic recombination from the
crossing over
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Accidents during Meiosis Usually, Meiosis is
accident-free, but sometimes not Nondisjunction
An accident where the members of the chromosome
pair fail to separate at Anaphase Can occur in
either Meiosis I or Meiosis II Result gametes
with abnormal chromosome numbers (p. 138-139 in
text)
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Figure 8.20
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Figure 8.21
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Table 8.1
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Klinefelter's Syndrome (XXY) Male sex organs
present, but testes abnormally small (he is
sterile due to this) Often has breast
enlargements and female body contours Some have
XXYY, XXXY, or XXXXY Many of these have
developmental disabilities as well as the above
symptoms
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XYY Male No defined syndrome, appears normal,
but taller than average XXX Female No defined
syndrome, can only tell by looking at karyotype
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Turner's Syndrome (XO) Female Have a short
stature, web of skin between neck and shoulders,
sex organs do not fully mature (making them
sterile) Normal intelligence Only non-fatal
condition where a human has only 45 chromosomes