| A diploid somatic cell from a rat has a total of 42 chromosomes \[\left( 2n\text{ }=\text{ }42 \right).\]Read the following statements and select the option with correct statements. |
| [A] Rat has 21 different chromosomes. |
| [B] Rat has 42 DNA molecules during \[{{G}_{1}}.\] |
| [C] Rat has 21 bivalents in metaphase A of meiosis. |
| [D] Rat has 42 DNA molecules in metaphase B of meiosis. |
A) [A] and [B]
B) [B] and [D]
C) [A], [B] and [C]
D) [A], [B], [C] and [D]
Correct Answer: D
Solution :
Every diploid rat cell contains 42 chromosomes, arranged as 21 pairs, with one member of a pair inherited from each parent at the time of conception. Before replication, one chromosome is composed of one DNA molecule. So, 42 chromosomes will have 42 DNA molecules. In metaphase I, each pair of bivalents (two chromosomes, four chromatids total) align on the metaphase plate. So, rat has 21 bivalents or pairs of homologous chromosomes on the metaphase plate. During metaphase II, rat cell contains 21 duplicated chromosomes so there will be 42 DNA molecules.
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