During meiosis, process of pairing of homologous chromosomes which permits large segments of DNA to be exchanged is known as:
Synapsis (pairing of homologous chromosomes) is a unique event that occurs only during meiosis I in the production of gametes. Synapsis is necessary so that crossing over, whereby large segments of DNA are exchanged, can occur. Prophase-I of Meiosis I-Is long & complex phase that differ considerably from mitotic prophase and is customarily divided into five sub- stages. 1.Leptotene: - Homologous chromosomes (maternal and paternal copies of the same chromosomes) begin to condense. 2. Zygotene: - Homologous chromosomes initiate pairing / synapsis. The pairs of synapsed homologous are known as Bivalent. The sex chromosomes also sta to synapse during zygotene. 3.Pachytene: - Synapsis is complete for all chromosomes. Genetic recombination between non-sister chromatids is completed at this point, with sites where it has occurred, appearing as recombination nodules in the center of the synaptonemal complex. 4.Diplotene: - Pairs of homologous chromosomes separates except where crossing over has occurred (chiasmata). This process is called disjunction. In the ovaries: - Primary oocyte gets arrested in diploteneby the fifth month is utero and each remains at this stage until the period before ovulation. (up to 50 years) 5.Diakinesis: -It is the prometaphase of the first meiotic division.
Crossing over
Non-disjunction
Alignment
Synapsis
Perfeilization, placenta and germ cell derivatives