Question

Tetrad is made of _______
A. Four homologous chromosomes with four chromatids
B. Two homologous chromosomes, each with two chromatids
C. Four non - homologous chromatids
D. Four non - homologous chromosomes

Answer 1

Hint:- At the time of cell division the chromatin material gets condensed to form chromosomes, thus chromosome is a highly condensed form of the chromatin. During the resting stage of cell division (interphase) chromosomes are not visible. When the cell divides it undergoes several stages like prophase, metaphase, anaphase and telophase. At the metaphase stage, each chromosome consists of two cylindrical structures called chromatids.

Complete Answer:-
In anaphase and telophase stage, a chromosome may have a single chromatid and in a prophase and metaphase stage, a chromosome has two chromatids. Each chromatid consists of a single long thread of DNA associated with histone. Non-histone proteins and RNA are also present. During meiotic division, prophase is divided into five distinct stages named as- leptotene, zygotene, pachytene, diplotene and diakinesis.
During leptotene, chromatin threads condense to form chromosomes. Then they enter the zygotene stage. Zygotene is characterised by the pairing of homologous chromosomes. These pairs of homologous chromosomes are called tetrad or bivalents. However, these are more clearly visible at the next stage called pachytene.
A structure called synaptonemal complex develops during zygotene in between the homologous chromosomes. Due to increased attraction, the homologous chromosomes tightly coil around each other. Both the chromatids of each chromosome become distinct and are called sister chromatids. The tetrad which is developed during the zygotene stage consists of four homologous chromosomes with four chromatids.

**Thus the correct answer is Four homologous chromosomes with four chromatids, option A.
**

Note:- Formation of bivalents or tetrad is the characteristic feature of first meiotic division. Recombination nodules are formed between non-sister chromatids of homologous pairs and these non-sister chromatids exchange their parts. This is called crossing over.
During the diplotene stage, the synaptonemal complex dissolves and the diakinesis is the end stage of the prophase of the first meiotic division.