Reminder: Test Corrections due on TUESDAY.
On Monday, 1st-4th periods will meet in the Media
Center, and 6th period will meet in Mr. Bennett’s
room (#246.) You’ll finish Chapter 13 and begin
Chapter 14 notes.
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FRQ Grading Update:
1st & 6th periods are DONE
2nd period will be done by this afternoon
I’ll do 4th period this weekend
3rd period: eh…
Ch 13 Meiosis and Sexual Life Cycles
1. What do you know about chromosomes?
- Made of chromatin – DNA + protein
- 23 pairs (46 total)
- 22 autosomes + 1 sex chromosome
- XX - ♀ - female
- XY - ♂ - male
2. What is the difference between haploid & diploid?
- haploid (n )
- cells with 1 set of chromosomes
- gametes - sperm & egg
- diploid (2n)
- somatic cells
- 2 sets of chromosomes (1 set – mom & 1 set dad)
Meiosis creates haploid gametes that unite to produce a diploid
zygote.
Figure 13.4 Describing chromosomes
Key
Maternal set of
chromosomes (n = 3)
2n = 6
Paternal set of
chromosomes (n = 3)
Two sister chromatids
of one replicated
chromosome
Centromere
Two nonsister
chromatids in
a homologous pair
Pair of homologous
chromosomes
(one from each set)
Ch 13 Meiosis and Sexual Life Cycles
1. What do you know about chromosomes?
2. What is the difference between haploid & diploid?
3. Where does meiosis occur in us?
- testes
Key
Haploid gametes (n = 23)
- ovaries
Haploid (n)
Ovum (n)
Diploid (2n)
Sperm
Cell (n)
FERTILIZATION
MEIOSIS
Ovary
Testis
Mitosis and
development
Multicellular diploid
adults (2n = 46)
Diploid
zygote
(2n = 46)
Ch 13 Meiosis and Sexual Life Cycles
1. What do you know about chromosomes?
2. What is the difference between haploid & diploid?
3. Where does meiosis occur in us?
4. What happens in meiosis? An overview.
- Preceded by DNA replication
- 2 consecutive cell divisions
- meiosis I – separation of homologous chromosomes
- meiosis II – separation of sister chromatids
- Makes 4 unique daughter cells. Genetically different from
- each other
- the parent cell
Figure 13.7 Overview of meiosis: how meiosis reduces
chromosome number
Interphase
Homologous pair
of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated chromosomes
Sister
chromatids
Diploid cell with
replicated
chromosomes
Meiosis I
1 Homologous
chromosomes
separate
Haploid cells with
replicated chromosomes
Meiosis II
2 Sister chromatids
separate
Haploid cells with unreplicated chromosomes
Ch 13 Meiosis and Sexual Life Cycles
1. What do you know about chromosomes?
2. What is the difference between haploid & diploid?
3. Where does meiosis occur in us?
4. What happens in meiosis? An overview.
5. What happens during meiosis? The specifics.
Figure 13.8 The Meiotic Division of an Animal Cell
MEIOSIS I: Separates homologous chromosomes
INTERPHASE
PROPHASE I
METAPHASE I
ANAPHASE I
Sister chromatids
remain attached
Centromere
(with kinetochore)
Centrosomes
(with centriole pairs)
Sister
chromatids
Nuclear
envelope
Chiasmata
Spindle
Metaphase
plate
Homologous
Microtubule
chromosomes
attached to
Chromatin
separate
kinetochore
Tetrads line up
Chromosomes duplicate Homologous chromosomes
(red and blue) pair and exchange
segments; 2n = 6 in this example
Tetrad
Pairs of homologous
chromosomes split up
Prophase I (90% of meiosis)
- Chromosomes condense
Synapsis occurs forming tetrads
- Centrosomes move apart
Chromsomes line-up gene-by-gene
- Nuclear envelope disappears Crossing over takes place at chiasmata
MEIOSIS II: Separates sister chromatids
TELOPHASE I AND
CYTOKINESIS
PROPHASE II
Cleavage
furrow
Two haploid cells
form; chromosomes
are still double
METAPHASE II
ANAPHASE II
Sister chromatids
separate
TELOPHASE II AND
CYTOKINESIS
Haploid daughter cells
forming
During another round of cell division, the sister chromatids finally separate;
four haploid daughter cells result, containing single chromosomes
Meiosis II – same as mitosis (separation of sister chromatids)
Ch 13 Meiosis and Sexual Life Cycles
1. What do you know about chromosomes?
2. What is the difference between haploid & diploid?
3. Where does meiosis occur in us?
4. What happens in meiosis? An overview.
5. What happens during meiosis? The specifics.
6. What are the differences between mitosis & meiosis?
- Meiosis is a reduction division…mitosis cells have the
same number of chromosomes.
- Meiosis creates genetic variation…mitosis produces a
clone.
- Meiosis is 2 consecutive nuclear divisions….mitosis just 1.
Figure 13.9 A comparison of mitosis and meiosis
MITOSIS
MEIOSIS
Chiasma (site of
crossing over)
Parent cell
(before chromosome replication)
MEIOSIS I
Prophase I
Prophase
Chromosome
replication
Duplicated chromosome
(two sister chromatids)
Chromosome
replication
Tetrad formed by
synapsis of homologous
chromosomes
2n = 6
Chromosomes
positioned at the
metaphase plate
Metaphase
Sister chromatids
separate during
anaphase
Anaphase
Telophase
2n
Tetrads
positioned at the
metaphase plate
Homologues
separate
during
anaphase I;
sister
chromatids
remain together
Metaphase I
Anaphase I
Telophase I
Haploid
n=3
Daughter
cells of
meiosis I
2n
MEIOSIS II
Daughter cells
of mitosis
n
n
n
Daughter cells of meiosis II
Sister chromatids separate during anaphase II
n
Ch 13 Meiosis and Sexual Life Cycles
1. What do you know about chromosomes?
2. What is the difference between haploid & diploid?
3. Where does meiosis occur in us?
4. What happens in meiosis? An overview.
5. What happens during meiosis? The specifics.
6. What are the differences between mitosis & meiosis?
7. What are the 3 ways meiosis creates genetic variation?
- Independent assortment of chromosomes (metaphase I)
- Crossing over (prophase I)
- Random fertilization
Figure 13.10 The independent assortment of homologous
chromosomes in meiosis
Key
Maternal set of
chromosomes
Possibility 1
Possibility 2
Paternal set of
chromosomes
Two equally probable
arrangements of
chromosomes at
metaphase I
Metaphase II
Daughter
cells
Combination 1
Combination 2
223 possible combinations in humans
Combination 3
Combination 4
Figure 13.11 The results of crossing over during meiosis
- Prophase I
- New chromosome combinations
- non-sister chromatids are exchanged
- 2 – 3 times per chromosome in humans
Prophase I
of meiosis
Nonsister
chromatids
Tetrad
Chiasma,
site of
crossing
over
Metaphase I
Metaphase II
Daughter
cells
Recombinant
chromosomes
Ch 13 Meiosis and Sexual Life Cycles
1. What do you know about chromosomes?
2. What is the difference between haploid & diploid?
3. Where does meiosis occur in us?
4. What happens in meiosis? An overview.
5. What happens during meiosis? The specifics.
6. What are the differences between mitosis & meiosis?
7. What are the 3 ways meiosis creates genetic variation?
- Independent assortment of chromosomes (metaphase I)
- Crossing over (prophase I)
- Random fertilization
-
-
223 = 8 million sperm
x
223 = 8 million egg
- 64 trillion unique combinations
- Genetic variation contributes to evolution via natural
selection