Meiosis

44 XY 44 XX

44 XY

22 X

22 X

22 Y

44 XX

SPERMSOVULES

SEX DETERMINISM IN HUMANS

HETEROGAMETIC SEX

HOMOGAMETIC SEX

4646

23

23

46

46

46 46

Variability causes in Meiosis

1.Homologous Chromosomes Separation during ANAPHASE I.

PROPHASE I

SYNAPSIS

CROSSING OVER

A A A AB B b bC C C C

D D D D

E E e eFG

F F F

G g g

AB

C

D

E

F

G

AB

C

D

e

F

g

AAb

C

D

e

F

g

b

C

D

E

F

G

Variability causes in Meiosis2. Crossing over

RECOMBINATION OF GENES

Random Crossing over between homologous chromosomes, as a result........Recombination

Recombination

Imagine that Recombination takes place only in one pair of Chromosomes. From the mother cell after Meiosis would appear four types of ovules.

Understanding Meiosis

MEIOSIS I

MEIOSIS: A GENERAL VISION

MEIOSIS II

Each body cell (Somatic Cell) contains two sets of chromosomes .One set comes from father and the another one comes from mother.

Human beings 46 Chromosomes.23 from father23 from mother.

ABCD1EF3G2H9

ABCD1EF3G2H9 I

JKLMN1O1PQ

IJKLMN1O1PQ

mother`s chromosome

father`s chromosome

AbCD2EF1G2H9

AbCD2EF1G2H9

iJkL2mN1O3Pq

iJkL2mN1O3Pq

HOMOLOGOUS

They take genes for the same Traits but can take different versions.Observe the Example.

SYNAPSIS

To match

matching

Crossing over and Recombination

The main events in Meiosis

2. Random Crossing over between homologous chromosomes

1.Homologous Chromosomes Separate during ANAPHASE I

RECOMBINATION OF GENES

MITOSIS OR MEIOSIS. Why?

12

34

5

6

HOMOLOGOUSHOMOLOGOUS

CHROMOSOMES ALIGN ALONG

METAPHASE PLATE

PROPHASE I

d) Anaphase I

PROPHASE II

i) Anaphase II

Variability causes in Meiosis

1. Crossing over

3.Separation of sister Chromatides during ANAPHASE II

2.Homologous Chromosomes Separation during ANAPHASE I

AB

C

D

E

F

G

AB

C

D

e

F

g

AAb

C

D

e

F

g

b

C

D

E

F

G

1. Crossing over

Exchange of Genetic Material between Homologous Chromosomes

2.Homologous Chromosomes Separation during ANAPHASE I

Either

or

A B

A B

A1A2

A1 A2

A3 A4 A3A4

ANAPHASE II

3.Separation of sister Chromatides during ANAPHASE II

CHROMOSOME CROSSING-OVERA B A A B B

C C C C

REPLICATION

S

HOMOLOGOUS

C C C C

CROSSING OVER

SYNAPSIS

matching

Chiasma

C C C C

CROSSING OVER

SYNAPSIS

C C C C

SYNAPSIS

CCCCCC

GAMETES