MEIOSISMEIOSIS

Object: to study the meiosis through Object: to study the meiosis through its subsequent developmental stages its subsequent developmental stages and discuss its Genetics Significant..and discuss its Genetics Significant..

• Meiosis in Meiosis in malesmales is called is called spermatogenesisspermatogenesis and produces and produces spermssperms..

• Meiosis in Meiosis in femalesfemales is called is called oogenesisoogenesis and and produces produces ovaova..

•Two divisionsTwo divisions ( (meiosis I meiosis I and and meiosis IImeiosis II).).

MeiosisMeiosis

2n

n

n

1 cell division: 1 cell division: 2 daughter cells2 daughter cells

2 cell divisions: 2 cell divisions: 4 cells product 4 cells product of meiosisof meiosis

2n

2n

2nn

n n

n

n=chromosome numbern=chromosome number

Somatic cellsSomatic cells

Cells in sexual cycleCells in sexual cycle

MITOSISMITOSIS

MEIOSISMEIOSIS

definitionsdefinitions

• Homologous Homologous chromosomes:chromosomes: the members of a the members of a chromosome pair chromosome pair that is identical that is identical in the in the arrangement of arrangement of genesgenes

Homologous ChromosomesHomologous Chromosomes

PaternalPaternal MaternalMaternal

eye coloreye color locuslocus

eye coloreye color locuslocus

hair colorhair color locuslocus

hair colorhair color locuslocus

• Synapsis: (Synapsis: (التشابكالتشابك)) the intimate association the intimate association

وثيق وثيق ترابط of ) of (((ترابطhomologous homologous chromosomes…chromosomes…

Homologous chromosomes

definitionsdefinitions

definitionsdefinitions

• Crossing-over: Crossing-over: ((العبورالعبور))

a term describing the a term describing the process of process of reciprocal reciprocal chromosomalchromosomal interchange by which interchange by which recombinants ariserecombinants arise

Crossing overPairing of

homologous chromosomesChiasmaChiasma formationChromosomes

Breakage and joining

Recombinant chromosomes

MEIOSIS I

• Prophase I

• The The longestlongest phase. phase. This phase can be This phase can be divided into 5 stages;divided into 5 stages;

a)a) LeptoteneLeptoteneb)b) ZygoteneZygotenec)c) PachytenePachytened)d) DiploteneDiplotenee)e) DiakinesisDiakinesis

1 .Leptotene

2.Zygotene

3.Pachytene 4.Diplotene 5.Diakinesis

Prophase I

Metaphase I Anaphase I

Telophase IProphase II

Prophase I

Meiosis 2Meiosis 2ndnd division: division: like mitosislike mitosis with haploid set with haploid set

4 Haploid cells Gametes4 Haploid cells Gametes

Mitosis vs MeiosisMitosis vs Meiosis

MitosisMitosis MeiosisMeiosisResults inResults in 2 Diploid Cells 2 Diploid Cells

(2N)(2N)4 Haploid Cells 4 Haploid Cells (N)(N)

Cells areCells are Genetically Genetically IdenticalIdentical

Genetically Genetically DifferentDifferent

Occurs inOccurs in Somatic (Body) Somatic (Body) CellsCells

Sex CellsSex Cells

Prophase IProphase I

Slides for Meiosis I & II:Slides for Meiosis I & II:

Metaphase I:Metaphase I:

Anaphase I:Anaphase I:

Telophase I:Telophase I:

Prophase II:Prophase II:

Metaphase II:Metaphase II:

Anaphase II:Anaphase II:

Telophase II:Telophase II:

Final result

 Meiosis :Four genetically different haploid cells from one diploid parent cell

Mitosis :two genetically identical diploid cells from one diploid parent cell