Meiosis is a reductional divison in which chromosomes number reduces into half. Meiosis occurs in Տҽ×ually reproducing organisms during the formation of haploid gametes. Meiosis is divided into two stages which ultimately give rise to four daughter cells. The two stages occur in meiosis are:-
- Meiosis I
- Meiosis II
Meiosis occurs during the formation of gametes that is during spermatogenesis and oogenesis. During meiosis, chromosomes number becomes half. Thus gametes have half number of chromosomes as contained in somatic cells. This ensures the same number of chromosomes in every generation because when haploid gametes fuse production of a diploid cell zygote is produced. If it does not happen that is ploidy level of gametes does not reduced and remains as that of somatic cells then after every fusion in each generation offspring would become the double ploidy as that of parent. Thus, ploidy level and number of chromosomes does not restored in this way.
Meiosis II is same as that of mitosis as a result of which ploidy level in both remains same as that of parent but meiosis I is different from both mitosis and meiosis II because it involves the reductional divison and change the ploidy level into half as that of parent for example if parent’s ploidy is diploid then it will reduces to haploid, thus ultimately produces four daughter cells instead of two daughter cells as produced in mitosis.
Recombination is a process of formation of new combinations. It occurs during meiosis. It is a process during which fragments of DNA are broken and recombine to create new allelic combinations. It generally occurs between the sister chromatids which creates genetic diversity at the level of genes thus reflect differences among organisms.
Recombination is a useful process occurs mainly during meiosis during which new combinations form. It is also important for the evolution. Recombination occurs by the following two mechanisms:-
- Unequal crossing over between non-sisters chromatids of homologous chromosomes.
- Independent assortment.
Crossing over occurs in the pachytene stage of Prophase of meiosis I. it involves the exchange of genetic material between the homologues chromosomes leads to the formation of new combinations during gamete formation. It occurs between the non-sister chromatids of homologous chromosomes which results in the recombination during Տҽ×ual reproduction. It is the final process of recombination occurs by a process called a synapsis.
Independent assortment is one of the Mandel’s laws of assortment. According to Mandel, allelic pair segregates independently during gamete formation (law of independent assortment). This means that organisms have combination of traits derived from the parents but not exactly same of either of the parent. Thus, the traits in an offspring are a combination of both the parents. Independent assortment allows the possibility of new trait advantageous which can be evolutionary benefit.
Complete the concept map as shown below:-