Describe the following: (a) Synapsis (b) Bivalent (c) Chiasmata

(a) Synapsis: Synapsis is a process that occurs during prophase I of meiosis, specifically during the zygotene stage. It involves the pairing of homologous chromosomes, forming structures known as bivalents or tetrads. Synapsis is facilitated by the formation of a protein structure called the synaptonemal complex, which holds the homologous chromosomes together along their lengths. This pairing allows for the exchange of genetic material between homologous chromosomes during crossing over, which contributes to genetic diversity among offspring.

(b) Bivalent: A bivalent, also known as a tetrad, is a structure formed during meiosis when two homologous chromosomes come together and pair up during synapsis. Each bivalent consists of four chromatids, with two chromatids from each homologous chromosome. The paired homologous chromosomes are aligned side by side, and the chromatids are closely associated along their lengths. Bivalents are essential for the proper segregation of homologous chromosomes during meiosis and play a key role in promoting genetic diversity through crossing over.

(c) Chiasmata: Chiasmata are cross-shaped structures that form at points of genetic recombination between homologous chromosomes during prophase I of meiosis. As homologous chromosomes undergo synapsis and crossing over, segments of genetic material are exchanged between chromatids, resulting in the formation of chiasmata. Chiasmata represent physical manifestations of genetic recombination, where segments of DNA are swapped between non-sister chromatids of homologous chromosomes. These exchanges of genetic material contribute to genetic diversity by producing novel combinations of alleles on the chromatids, which are then inherited by the offspring. Chiasmata are visible under a microscope and can be observed as physical connections between homologous chromosomes during late prophase I and metaphase I of meiosis.