MeiosisMeiosis

Fig. 13-3bFig. 13-3b

TECHNIQUE

Pair of homologousreplicated chromosomes

Centromere

Sisterchromatids

Metaphasechromosome

5 µm

Fig. 13-6Fig. 13-6

Key

Haploid (n)

Diploid (2n)

n nGametes

nn n

Mitosis

MEIOSIS FERTILIZATION

MEIOSIS

2n 2nZygote2n

Mitosis

Diploidmulticellularorganism

(a) Animals

Spores

Diploidmulticellularorganism(sporophyte)

(b) Plants and some algae

2n

Mitosis

Gametes

Mitosisn

nn

Zygote

FERTILIZATION

n

n

nMitosis

Zygote

(c) Most fungi and some protists

MEIOSIS FERTILIZATION

2n

Gametes

n

n

Mitosis

Haploid multi-cellular organism(gametophyte)

Haploid unicellular ormulticellular organism

Key

Haploid (n)

Diploid (2n)

n n

n

nn

2n2n

Mitosis

Mitosis

Mitosis

Zygote

SporesGametes

MEIOSIS FERTILIZATION

Diploidmulticellularorganism(sporophyte)

Haploid multi-cellular organism(gametophyte)

(b) Plants and some algae

Terms to know. . .

Somatic vs germ line cells Chromosomes (13.6)

Chromatids Homologous Autosomes vs sex chromosomes

Locus

Key

Maternal set ofchromosomes (n = 3)

Paternal set ofchromosomes (n = 3)

2n = 6

Centromere

Two sister chromatidsof one replicatedchromosome

Two nonsisterchromatids ina homologous pair

Pair of homologouschromosomes(one from each set)

KeyHaploid (n)Diploid (2n)

Haploid gametes (n = 23)

Egg (n)

Sperm (n)

MEIOSIS FERTILIZATION

Ovary Testis

Diploidzygote(2n = 46)

Mitosis anddevelopment

Multicellular diploidadults (2n = 46)

Different Chromosome Numbers Are Found in One Organism

Gametes contain half as many chromosomes as somatic cells

Zygotes are produced by fusion of gametes Fusion of gametes is called fertilization or syngamy Meiosis serves to stabilize the chromosomes number Is a reduction division process Gametes are haploid and possess a single set of genetic material

An individual inherits genes from its father and its mother

I.Sexual Reproduction Varies by Kingdom A. Unicellular organisms 1. Individual cells function directly as

gametes 2. Zygote may divide mitotically or meiotically B. Plants 1. Haploid cells are produced through meiosis 2. Cells divide mitotically to form multicellular

haploid phase 3. Special haploid cells differentiate into

eggs or spermC. Animals

1. Gamete-producing cells differentiate from somatic cells early

2. Referred to as germ line cells 3. Somatic cells are diploid and reproduce by mitosis 4. Diploid gamete-producing cells, produce

haploid gametes by meiosis

If you think you can you can.

If you think you can’t you're right.

Prophase I Metaphase I Anaphase ITelophase I and

CytokinesisProphase II Metaphase II Anaphase II Telophase II and

Cytokinesis

Centrosome(with centriole pair)

Sisterchromatids Chiasmata

Spindle

Homologouschromosomes

Fragmentsof nuclearenvelope

Centromere(with kinetochore)

Metaphaseplate

Microtubuleattached tokinetochore

Sister chromatidsremain attached

Homologouschromosomesseparate

Cleavagefurrow

Sister chromatidsseparate Haploid daughter cells

forming

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Meiosis I

Interphase: replication Each chromosome = 2 sister chromatids

Prophase I: Condensation of chromatin Synapsis Tetrads form Crossing over @ chiasmata Centrosomes separate, spindles form, bind to

kinetochores

Meiosis I

Metaphase I: Tetrads line up on metaphase plate

Anaphase I: Chromosomes (each = 2 sister chromatids) move to poles

Pulled along fibers by kinetochore Centromeres don’t separate

Telophase/cytokinesis Cleavage furrow N set of chromosomes @ each pole DAUGHTER CELLS ARE HAPLOID

Fig. 13-8bFig. 13-8b

Prophase I Metaphase I

Centrosome(with centriole pair)

Sisterchromatids Chiasmata

Spindle

Centromere(with kinetochore)

Metaphaseplate

Homologouschromosomes

Fragmentsof nuclearenvelope

Microtubuleattached tokinetochore

Fig. 13-UN4Fig. 13-UN4

Fig. 13-8cFig. 13-8c

Anaphase ITelophase I and

Cytokinesis

Sister chromatidsremain attached

Homologouschromosomesseparate

Cleavagefurrow

Fig. 13-8dFig. 13-8d

Prophase II Metaphase II Anaphase II Telophase II andCytokinesis

Sister chromatidsseparate Haploid daughter cells

forming

Meiosis II(NO INTERPHASE) Prophase II

New spindle fibers form Chromosomes move to middle

Metaphase II: Chromosomes on metaphase plate

Anaphase II: Centromeres/sister chromatids separate Each chromosome now = 1 chromatid

Telophase II/cytokinesis Nuclear membrane forms

Fig. 13-8eFig. 13-8e

Prophase II Metaphase II

Fig. 13-8fFig. 13-8f

Anaphase IITelephase II and

Cytokinesis

Sister chromatidsseparate Haploid daughter cells

forming

Fig. 13-8Fig. 13-8

Prophase I Metaphase I Anaphase ITelophase I and

CytokinesisProphase II Metaphase II Anaphase II Telophase II and

Cytokinesis

Centrosome(with centriole pair)

Sisterchromatids Chiasmata

Spindle

Homologouschromosomes

Fragmentsof nuclearenvelope

Centromere(with kinetochore)

Metaphaseplate

Microtubuleattached tokinetochore

Sister chromatidsremain attached

Homologouschromosomesseparate

Cleavagefurrow

Sister chromatidsseparate Haploid daughter cells

forming

Fig. 13-UN1Fig. 13-UN1

Prophase I: Each homologous pair undergoessynapsis and crossing over between nonsisterchromatids.

Metaphase I: Chromosomes line up as homolo-gous pairs on the metaphase plate.

Anaphase I: Homologs separate from each other;sister chromatids remain joined at the centromere.

Fig. 13-11-2Fig. 13-11-2

SUMMARY

MeiosisMitosisProperty

DNAreplication

Number ofdivisions

Occurs during interphase beforemitosis begins

One, including prophase, metaphase,anaphase, and telophase

Synapsis ofhomologouschromosomes

Does not occur

Number ofdaughter cellsand geneticcomposition

Two, each diploid (2n) and geneticallyidentical to the parent cell

Role in theanimal body

Enables multicellular adult to arise fromzygote; produces cells for growth, repair,and, in some species, asexual reproduction

Occurs during interphase before meiosis I begins

Two, each including prophase, metaphase, anaphase, andtelophase

Occurs during prophase I along with crossing overbetween nonsister chromatids; resulting chiasmatahold pairs together due to sister chromatid cohesion

Four, each haploid (n), containing half as many chromosomesas the parent cell; genetically different from the parentcell and from each other

Produces gametes; reduces number of chromosomes by halfand introduces genetic variability among the gametes

OOGENESIS/SPERMATOGENESIS

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Genetic Variation

Independent assortment of maternal/paternal chromosomes (13.9) How many pairs in a human?!?!?

Crossing over Exchange b/w homologous chromosmes Recombinant: genetic info from 2 sources Sister chromatids identical

Random fertilization

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