Describe the following.

(a) Synapsis

(b) Bivalent

(c) Chiasmata

Draw a diagram to illustrate your answer.

Asked by Abhisek | 11 months ago |  88

1 Answer

Solution :-

(a) Synapsis

● During zygotene of prophase-I of meiosis homologous chromosomes start pairing together and this process of association is called synapsis.

● Electron micrographs of this phase reveal that chromosome synapsis is accompanied by the formation of a complex structure known as synaptonemal complex among the synapsed chromosomes.

● Pairing is taking place in a zipper-like fashion.

(b) Bivalent

• The complex established by a pair of synapsed homologous chromosomes is known as a tetrad or a bivalent i.e., a pair of chromosomes or four chromatids.

• A bivalent contains two centromeres and four chromatids.

(c) Chiasmata

• Chiasmata are cross-like structures that appear in synapsed chromosomes. They characterize sites at which crossing over has taken place.

• Crossing over is the exchange of gene segments among non-sister chromatids of homologous chromosomes.

• Crossing over takes place at the pachytene stage, however, chiasmata are visible in the diplotene stage of prophase 1 of meiosis.

Following diagram shows the synapsis, bivalent and chiasma formation.

Textbook Solution

Answered by Pragya Singh | 11 months ago

Related Questions

Analyse the events during every stage of cell cycle and notice how the following two parameters change

(i) number of chromosomes (N) per cell

(ii) amount of DNA content (C) per cell

Class 11 Biology Cell Cycle and Cell Division View Answer

Discuss with your teacher about

(i) haploid insects and lower plants where cell-division occurs.

(ii) some haploid cells in higher plants where cell-division does not occur.

Class 11 Biology Cell Cycle and Cell Division View Answer