Why does reduction of chromosomes takes place in meiosis 1? What is its significance?
1 Answer
Reduction of chromosomes occurs so that the gametes formed subsequently have half the number of chromosomes and the original number is restored when the male and female gametes fuse to form zygote.
Explanation:
Meiosis occurs either at the time of gamete formation or at some stage prior to that. Cells undergoing meiosis are diploid. Reduction of chromosomes occurs in meiosis-1 to form 2 cells which undergo meiosis-2 to form four haploid cells (having half the number of chromosomes of the cell that undergoes meiosis). Meiosis 2 is just like mitosis.
Reduction of chromosomes occurs in meiosis 1 so that original diploid number is restored in zygote formed by the fusion of haploid gametes. Had there been no reduction, the number of chromosome would have multiplied generation after generation.
Meiosis 1 , besides causing reduction in number of chromosomes, is of significance as described below:
Meiosis is responsible for independent segregation of genes present on two homologous chromosomes, which are inherited from male and female parent . Independent segregation occurs during:
1. Crossing over taking place during prophase 1 stage.
2. Random orientation of bivalents at metaphase 1 stage.
Mendel's laws of segregation and law of independent assortment can be explained on the basis of chromosome behaviour during meiosis 1.
