Question

Mitosis and meiosis are both important processes of cell division in the life cycle of a sexual organism.

1. Discuss why both processes are necessary.

2. List the differences between Prophase of mitosis and Prophase I of meiosis. How do these differences contribute/ lead to genetic variation?

Answer 1

Both mitosis and meiosis are very important in the process of cell division.

1. Usually mitosis gives two identical copies of the cell means the daughter cell will be having exact same number of chromosomes, this means same genes, same proteins, same function, same character as parent cell. Mitosis occurs in somatic cells or non-germ cell, Germ cells are made by meiosis where number of chromosomes must be half for sperm and egg.

2. Prophase of mitosis-

1. Chromosomes are dense, and a pair of sister chromatid is attached with centromere.

2. Disappearance of the nucleolus in the beginning and disappearance of nuclear envelope in the end of prophase.

3. Mitotic spindle are formed between the two pairs of centriolesand migrate to opposite poles of the cell.

Prophase of meiosis-

Prophase 1-

Laptotene- Chromosomes are thread like.

Zygotene- Homologous pairing occur, synapsis will occur, synaptonemal complex will be formed, chromosomes are bivalant or tetrad.

Pachytene- Chromosomes will appear, crossing over will occur in between non sister chromatid.

Diplotene- Crossing over visualization, chaisma will be formed, nuclear membrane dissappearance, X like structure chaisma will be seen.

Diakinesis- Terminalization of chaisma, means reach at terminus.

Prophase 2- Spindle fibers reform and attach to centromeres.

In meiosis-

1. Crossing over is the main reason for genetic variation.

2. Meiosis having two stages, so amount of genetic material will be halved.

3. Recombination is there and synapsis formation is also there.