Question

A tetrad consists of
A. Four non-homologous chromatids
B. Four non-homologous chromosomes
C. Two sets of homologous chromosomes, each with two chromatids
D. Four homologous pairs of chromosomes

Answer 1

Hint: The content of chromatin is condensed to form chromosomes at the time of cell division, so chromosomes are a highly condensed form of chromatin. During the resting phase of cell division, chromosomes are not apparent (interphase). It goes through several stages as the cell divides, such as prophase, metaphase, anaphase and telophase. Each chromosome consists of two cylindrical structures called chromatids.

Complete answer: A chromosome can have a single chromatid in the anaphase and telophase stages, and a chromosome has two chromatids in the prophase and metaphase stages. Every chromatid consists of a single long thread of histone-associated DNA. Non-histone proteins and RNA are also present. The prophase is divided into five separate stages called leptotene, zygotene, pachytene, diplotene and diakinesis during meiotic separation. Chromatin threads are condensed to form chromosomes during the leptotene stage. They then enter the zygotene stage. The pairing of homologous chromosomes is the characteristic feature of zygotene. These pairs of homologous chromosomes are called bivalents or tetrads. However, they are more clearly evident at the next stage, called the pachytene stage. A structure known as the synaptonemal complex forms between homologous chromosomes during the zygotene phase. The homologous chromosomes are closely coiled around each other due to increased attraction. Both chromatids of each chromosome become separate and are called sister chromatids. During the zygotene phase, the tetrad consists of four homologous chromosomes with four chromatids.
Hence, option C is the correct answer.

Note: The characteristic feature of the first meiotic division is the creation of bivalents or tetrads. Recombination nodules are formed between non-sister chromatids of homologous pairs and these non-sister chromatids exchange their parts, which is called the crossover. The synaptonemal complex dissolves during the diplotene phase, and the diakinesis is the final stage of the prophase of the first meiotic division.