Ch 13 Meiosis and Sexual Life CyclesTest Corrections – Ch 9 – 12 Due on Friday

Ch 13 Meiosis and Sexual Life Cycles1. 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

KeyHaploid (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

nn

n

n

n

2n2n

2n 2n2nZygote

GametesHaploid multicellular

organism (gametophyte)Haploid multicellular

organism

HaploidDiploid

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

InterphaseHomologous 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

MetaphaseChromosomespositioned 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