Question

Compare and contrasts meiosis and mitosis.  How do the behavior of chromosomes during meiosis generate variation and explain Mendel’s law of independent assortment? Long answer, please.

Answer 1

In both mitosis and meiosis cell passes through Prophase, Metaphase, Anaphase and Telopahse stages. These stages are followed by cytokinesis. Basic events occurring in these two divisions are same. Except that the meiosis brings reduction in cell divisions and genetic recombinations. So meiosis can lead to evolution in populations.

2. Meiosis can bring genetic variations because of crossing over . During the process of crossing over, small bits of chromatids between homologous chromosomes are exchanged. This exchange changes the allele combinations between the homologous chromosomes. Because of this a population can have more variations in its individuals. Example, supposing mother is fair and short, father is dark and tall, ( suppose genes for complexion and height are on the same chromosome) offspring can be fair and tall and dark and short. Here we see, combination of traits change. Such changes in combination of alleles will cause variety in the population resulting in evolution. Because different allele of the genes coming together and certain alleles separating from one another during the process of crossing over, huge variety can be seen in the populations.

3. As per independent assortment, genes assort independent of each other during inheritance. Assortment of gene controlling one trait is independent of the gene controlling another trait. That is why variety of gametes are produced, not just parental combinations.

This is because during meiosis chromosomes assort independent of one another. Maternal and paternal chromosomes pair up and arrange on the equator of the cell and move to opposite poles independent of each other. Because of the chromosomal assortment, even the genes present on the chromosomes also assort independently. The offspring produced can have any combination of the genes.

Such independent assortment of genes is possible only if the genes are present on different chromosomes.