Question

Questions

Draw the stages of MITOSIS AND MEIOSIS with correct chromosome numbers in each stage, and be able to label the chromatid, tetrads, mitotic spindle, and kinetochores and explain what is happening and why?

Answer 1

MITOSIS:

In mitosis the number of chromosomes remain same in all stages.

Here in the diagram 2 chromosomes are shown in each cell.

Only the amount of genetic material decreases which is again formed in the next cell cycle.

Stages:

Prophase: it is divided into early prophase and late prophase.

All the organelles disintegrate.

Nuclear membrane disintegrate.

Chromatin gets converted into chromosome. (So that they don't break while dividing)

Centrioles get divided and move to opposite poles.

Metaphase: chromosomes are arranged at the centre forming a metaphase plate.

Spindle fibres attach to the kinetochores of the chromosomes.

Anaphase : kinetochores split, chromatids separate and move towards the opposite poles.

Telophase: chromatids reach to their respective poles. Nuclear membrane forms.

Cytokinesis: after nuclear division cytoplasm also divides.

MEIOSIS:

Meiosis has 2 stages- meiosis 1 and meiosis 2.

In meiosis 1 the number of chromosomes reduces to half.

Meiosis 2 is same as mitosis so chromosome number remain same.

MEIOSIS 1:

In meiosis 1 the stages are:

A cell having 4 chromosomes entering into meiosis 1.

A) Prophase 1: it is divided into

Leptotene- chromosomes become visible

Zygotene- synapsis and tetrad formation. Tertad is paired homologous chromosomes.

Pachytene- crossing over takes place

Diplotene- chaismata visible.

Diakinesis- terminalisation of chaismata.

B) Metaphase 1:

A double metaphase plate is formed by tetrads moving to the centre.

Spindle fibres attach to the kinetochores of the homologous chromosomes.

C) Anaphase 1: homologous chromosomes separate and move towards the opposite poles.

D) Telophase 1: nuclear membrane appears.

2 nucleus with 2 chromosomes each are formed.

E) Cytokinesis 1: division of cytoplasm. Formation of two cells having 2 chromosomes each.

MEIOSIS 2:

In meiosis 1 two cells were formed having 2 chromosomes each.

Here we are showing meiosis 2 with one the two cells.

Prophase 2: nuclear membrane disintegrate

Metaphase 2: metaphase plate formed. Spindle fibres attach to the kinetochores.

Anaphase 2: sister chromatids separate and move towards the opposite poles.

Telophase 2: nuclear membrane appears.

As 2 cells were formed in meiosis 1, other cell also undergoes meiosis 2 .

Total 4 cells are produces with 2 chromosomes each.