13 Meiosis and Sexual Life Cycl t Corrections – Ch 9 – 12 Due on Friday
Jan 19, 2016
Ch 13 Meiosis and Sexual Life CyclesTest Corrections – Ch 9 – 12 Due on Friday
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.
Key
Maternal set ofchromosomes (n = 3)
Paternal set ofchromosomes (n = 3)
2n = 6
Two sister chromatidsof one replicatedchromosome
Two nonsisterchromatids ina homologous pair
Pair of homologouschromosomes(one from each set)
Centromere
Figure 13.4 Describing chromosomes
Ch 13 Meiosis and Sexual Life Cycles1. What do you know about chromosomes?2. What is the difference between haploid & diploid?3. Where does meiosis occur in us?
- testes- ovaries
Key
Haploid (n)Diploid (2n)
Haploid gametes (n = 23)
Ovum (n)
SpermCell (n)
MEIOSIS FERTILIZATION
Ovary Testis Diploidzygote(2n = 46)
Mitosis anddevelopment
Multicellular diploidadults (2n = 46)
Ch 13 Meiosis and Sexual Life Cycles1. What do you know about chromosomes?2. What is the difference between haploid & diploid?3. Where does meiosis occur in us?4. Let’s check out meiosis in other organisms…plants & fungi
Diploidmulticellular
organism
Key
MEIOSIS FERTILIZATION
MEIOSIS FERTILIZATION
MEIOSIS FERTILIZATION
n
n
n
n n
n
n n
n
n
n
n
n
2n2n
2n2n2n
Zygote
GametesHaploid multicellular
organism (gametophyte)Haploid multicellular
organism
Haploid
Diploid
Mitosis Mitosis
SporesGametes
Mitosis Mitosis
Gametes
Mitosis
Zygote
ZygoteMitosis
(a) Animals
Diploidmulticellularorganism(sporophyte)
(b) Plants and some algae (c) Most fungi and some protists
Ch 13 Meiosis and Sexual Life Cycles1. What do you know about chromosomes?2. What is the difference between haploid & diploid?3. Where does meiosis occur in us?4. Let’s check out meiosis in other organisms…plants & fungi.5. 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
Interphase
Homologous pairof chromosomesin diploid parent cell
Chromosomesreplicate
Homologous pair of replicated chromosomes
Sisterchromatids Diploid cell with
replicatedchromosomes
1
2
Homologous chromosomes separate
Haploid cells withreplicated chromosomes
Sister chromatids separate
Haploid cells with unreplicated chromosomes
Meiosis I
Meiosis II
Figure 13.7 Overview of meiosis: how meiosis reduces chromosome number
Ch 13 Meiosis and Sexual Life Cycles1. What do you know about chromosomes?2. What is the difference between haploid & diploid?3. Where does meiosis occur in us?4. Let’s check out meiosis in other organisms…plants & fungi.5. What happens in meiosis? An overview.6. What happens during meiosis? The specifics.
Centrosomes(with centriole pairs)
Sisterchromatids
Chiasmata
Spindle
Tetrad
Nuclearenvelope
Chromatin
Centromere(with kinetochore)
Microtubuleattached tokinetochore
Tetrads line up
Metaphaseplate
Homologouschromosomesseparate
Sister chromatidsremain attached
Pairs of homologouschromosomes split up
Chromosomes duplicate Homologous chromosomes(red and blue) pair and exchangesegments; 2n = 6 in this example
INTERPHASE MEIOSIS I: Separates homologous chromosomes
PROPHASE I METAPHASE I ANAPHASE I
Figure 13.8 The Meiotic Division of an Animal Cell
Prophase I (90% of meiosis)- Chromosomes condense - Centrosomes move apart- Nuclear envelope disappears
Synapsis occurs forming tetradsChromsomes line-up gene-by-geneCrossing over takes place at chiasmata
TELOPHASE I ANDCYTOKINESIS
PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II ANDCYTOKINESIS
MEIOSIS II: Separates sister chromatids
Cleavagefurrow Sister chromatids
separate
Haploid daughter cellsforming
During another round of cell division, the sister chromatids finally separate;four haploid daughter cells result, containing single chromosomes
Two haploid cellsform; chromosomesare still double
Meiosis II – same as mitosis (separation of sister chromatids)
Test corrections (if done)- Staple behind the test- Tuck scantron inside test- Place in box
Can transport – Wednesday – all day & 4:30 loading
Ch 13 Meiosis and Sexual Life Cycles1. What do you know about chromosomes?2. What is the difference between haploid & diploid?3. Where does meiosis occur in us?4. Let’s check out meiosis in other organisms…plants & fungi.5. What happens in meiosis? An overview.6. What happens during meiosis? The specifics.7. 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.
MITOSIS MEIOSIS
Prophase
Duplicated chromosome(two sister chromatids)
Chromosomereplication
Chromosomereplication
Parent cell(before chromosome replication)
Chiasma (site ofcrossing over)
MEIOSIS I
Prophase I
Tetrad formed bysynapsis of homologouschromosomes
Metaphase
Chromosomespositioned at themetaphase plate
Tetradspositioned at themetaphase plate
Metaphase I
Anaphase ITelophase I
Haploidn = 3
MEIOSIS II
Daughtercells of
meiosis I
Homologuesseparateduringanaphase I;sisterchromatidsremain together
Daughter cells of meiosis II
n n n n
Sister chromatids separate during anaphase II
AnaphaseTelophase
Sister chromatidsseparate duringanaphase
2n 2nDaughter cells
of mitosis
2n = 6
Figure 13.9 A comparison of mitosis and meiosis
Ch 13 Meiosis and Sexual Life Cycles1. What do you know about chromosomes?2. What is the difference between haploid & diploid?3. Where does meiosis occur in us?4. Let’s check out meiosis in other organisms…plants & fungi.5. What happens in meiosis? An overview.6. What happens during meiosis? The specifics.7. What are the differences between mitosis & meiosis?8. What are the 3 ways meiosis creates genetic variation?
- Independent assortment of chromosomes (metaphase I)- Crossing over (prophase I)- Random fertilization
Key
Maternal set ofchromosomes
Paternal set ofchromosomes
Possibility 1
Two equally probable arrangements ofchromosomes at
metaphase I
Possibility 2
Metaphase II
Daughtercells
Combination 1 Combination 2 Combination 3 Combination 4
Figure 13.10 The independent assortment of homologous chromosomes in meiosis
223 possible combinations in humans
Prophase Iof meiosis
Nonsisterchromatids
Tetrad
Chiasma,site ofcrossingover
Metaphase I
Metaphase II
Daughtercells
Recombinantchromosomes
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 us
Ch 13 Meiosis and Sexual Life Cycles1. What do you know about chromosomes?2. What is the difference between haploid & diploid?3. Where does meiosis occur in us?4. Let’s check out meiosis in other organisms…plants & fungi.5. What happens in meiosis? An overview.6. What happens during meiosis? The specifics.7. What are the differences between mitosis & meiosis?8. 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