Describe the following: (a) synapsis (b) bivalent (c) chiasmata Draw a diagram to illustrate your answer.

(a) Synapsis

• Synapsis is the process during which homologous chromosomes pair up lengthwise during prophase I of meiosis, specifically in the zygotene stage.

• This pairing is facilitated by the formation of a proteinaceous structure called the synaptonemal complex.

• Synapsis ensures precise alignment of homologous chromosomes, which is essential for accurate genetic recombination and subsequent segregation.

(b) Bivalent

• A bivalent, also known as a tetrad, is the structure formed by a pair of homologous chromosomes that have undergone synapsis during prophase I of meiosis.

• Each bivalent consists of four chromatids (two from each homologous chromosome).

• The formation of bivalents is crucial for the process of crossing over, which leads to genetic variation in gametes.

(c) Chiasmata

• Chiasmata (singular: chiasma) are the visible X-shaped structures that represent the points where non-sister chromatids of homologous chromosomes have exchanged genetic material during crossing over.

• They become apparent during the diplotene stage of prophase I in meiosis.

• Chiasmata play a critical role in holding homologous chromosomes together until they are separated during anaphase I, ensuring accurate chromosome segregation.