Question

need to know both answers to A and B

A. Outline the stages of meiosis(showing crossing over, recombination of DNA, etc.)

B. what is the function of meiosis?

Answer 1

A.Stages of meiosis.

Meiosis Occur in 2 Stages-Meiosis 1 and Meiosis 2.

Meiosis 1 have following stages-

1.Prophase 1:

*chromosomes condense

*Nuclear envelope breaks down

*All chromosome aligns with its homologues chromosome

*Homologues Chromosomes exchange a part of their DNA(The process called Crossing Over).

[ This procees ocur with the help of synaptonemal complex, which is a Protein complex that holds the homologues chromosomes together].

*Each chromosome will attaches to microtubules.This attachment is just from one pole of the spindle.So the two homologues chromosomes of a pair bind to microtubules from opposite poles.

2.Metaphase 1:

*Homologues Chromosomes line up at the metaphase plate(Equator of the cell)

*Orientation of each pair occur randomly

3.Anaphase 1:

*Homologues Chromosomes are pulled away & move to opposite ends of the cell.

*Sister Chromatids remains Attached to One another.

4.Telophase 1 :

*Each chromosomes will arrive at opposite poles of the cell.

*Nuclear membrane re-forms.

*chromosomes decondense again.

Then the cells Enter Meiosis 2,

[Cells that enter Meiosis 2 are haploid,that is they have just 1 chromosome from each homologue pair.But their chromosomes still consist of two sister chromatids.During Meiosis 2--Sister chromatids separate & make haploid cells]

Meiosis 2 contains the following stages-

5.Prophase 2:

*chromosomes condense

*Nuclear envelope breaks down

*centrosomes will move away[spindle forms between them]

*The 2 sister chromatids of each chromosome will be captured by microtubules from opposite spindle poles.

6.Metaphase 2:

*individuall chromosomes line up along the metaphase plate.

7.Anapahse 2:

*Sister chromatids separate

*Sister chromatids pulled towards opposite poles of the cell

8.Telophase 2:

*Nuclear membranes form around each chromosomes

*Chromosomes decondense.

Then,Cytokinesis (Cell division)splits chromosome sets into new cells.

So the final products of meiosis contains four haploid cells in which each chromosome has just one chromatid.

B.Meiosis Important function is the production of gametes.

In Diploid Organisms,The 2 Gametes(Male & Female) gametes formed should be Haploid,So that they fuses together which eventually leads to Formation of Diploid Offsprings.

So inorder to make Haploid cells from Diploid cells Meiosis should occur(Mitosis of Diploid cells results in Diploid Cells).

So meiosis Helps in the formation of Haploid Gametes and helps in the Genomic Stability