Question

1. Explain the genome present in diploid cells and in haploid cells. 

2. Explain the purpose of mitosis in sexually reproducing organisms (example: your body cells). 

3. Explain the purpose of meiosis in sexually reproducing organisms (example: specific cells in your body).

Answer 1

1.

In diploid cells, there two copies of every chromosome. Where as in haploid cells, there is is one copy of every chromosome.

In case of diploid cells, the two chromosomes of a pair undergo recombination during meiosis. Where are in haploid cells there is no such event of recombination because the other counterpart of chromosome to pair is absent.

2.

Mitosis is the type of cell division which leads to the formation of daughter cells whose chromosome number and chromosome composition is identical to that of the parent cell. Each parent cell produces two daughter cells. Therefore the importance of mitosis is only to maintain the somatic or vegetative body of an individual. It helps in the growth of the body and also aids in repair processes in case of injury.

3.

Meiosis is the type of cell division which leads to variation among progeny and between progeny and parents. This is because it undertakes two events -

1. Crossing over between non sister chromatids of homologous chromosomes during prophase 1 of meiosis 1. In this phenomena, genetic material is exchanged between non sister chromatids. Each homologous chromosome contains two chromosomes, one from the paternal side and one from the maternal side. Crossing over, which is also known as recombination, between these two chromosomes results in the chromosomes which now contain some alleles of the paternal side and some alleles of the maternal side. Each chromosome therefore becomes a Recombinant chromosome.

( in mitosis there is no such process, there for each chromosome formed in the end is identical to the chromosome present in the parent cell)

2. Independent assortment of chromosomes of a homologous pair towards the opposite pole of the cell during anaphase 1 of meiosis 1. Each chromosome of a pair separate independently of the Other chromosome and move towards the opposite pole of the cell. Now each pole contains some chromosomes of the paternal side and some chromosomes of the maternal side.

( homologous chromosomes do not separate in mitosis, rather identical sister chromatids separate from each other and therefore the daughter cells formed in the under identical to Parent cell)

In this way the gametes formed in the end of meiosis 2 contains some chromosomes from the maternal side and some chromosome from the paternal side and also each chromosome contains some alleles from the maternal side and some alleles from the paternal side.

Please note that, when I say each chromosome becomes a Recombinant chromosome in point number 1, it doesn't mean that each chromosome is 50% parental and 50% maternal. After recombination a paternal chromosome contains a very few alleles of maternal chromosome and maternal chromosome contains a very few areas of paternal chromosome. Recombination occurs at a very small region and not throughout the chromosome.