describe the prophase I stage of meiosis using homologous chromosomes, synapsis, crossing over and chiasmata.
what is the significance of second meiotic division.
describe the prophase I stage of meiosis using homologous chromosomes, synapsis, crossing over and chiasmata.
what is the significance of second meiotic division.
Prophase 1: Prophase 1 of meiosis 1 is longest complex phase and divisible into five stages. They are leptotene, zygotene,pachytene, diplotene and diakinesis.
There are 2 sets of chromosomes in a diploid cell undergoing meiosis, one set contributed by the male parent and other by female parent. There are always two similar chromosomes, having same size, form and structure. They are called homologous chromosomes.
The side-by-side association of homologous paternal and maternal chromosomes during the first prophase of meiosis is known as synapsis.
Crossing over occurs during pachytene. Crossing over, (recombination) involves mutual exchange of the corresponding segments of non sister chromatids.
Separation of homologous chromosomes does not take place the points called chiasmata. The chiasmata mark the sites where crossing over occurred in pachytene.
Significance of meiosis 2:
The chromososmes that separate in the anaphase of meiosis 1 are still double. Each consists of two chromatids and has 2X amount of DNA. Thus, reduction to haploidy in terms of DNA content does not occur in Meiosis 1. Truly haploid nuclei in terms of DNA content as well as chromosome number of each chromosome are separated into two different nuclei. Thus meiosis 2 is necessary.
Prophase 1: Prophase 1 of meiosis 1 is longest complex phase and divisible into five stages. They are leptotene, zygotene,pachytene, diplotene and diakinesis.
There are 2 sets of chromosomes in a diploid cell undergoing meiosis, one set contributed by the male parent and other by female parent. There are always two similar chromosomes, having same size, form and structure. They are called homologous chromosomes.
The side-by-side association of homologous paternal and maternal chromosomes during the first prophase of meiosis is known as synapsis.
Crossing over occurs during pachytene. Crossing over, (recombination) involves mutual exchange of the corresponding segments of non sister chromatids.
Separation of homologous chromosomes does not take place the points called chiasmata. The chiasmata mark the sites where crossing over occurred in pachytene.
Significance of meiosis 2:
The chromososmes that separate in the anaphase of meiosis 1 are still double. Each consists of two chromatids and has 2X amount of DNA. Thus, reduction to haploidy in terms of DNA content does not occur in Meiosis 1. Truly haploid nuclei in terms of DNA content as well as chromosome number of each chromosome are separated into two different nuclei. Thus meiosis 2 is necessary.
