Question

In diploid zygote, chromosome number is 40. Chromosome number in a gamete will be
A. 10
B. 20
C. 30
D. 40

Answer 1

Chromosomes can be defined as oval, rod or thread like DNA and protein complexes that stores, replicates and transcribes the coded hereditary information. It was first observed by Hofmeister in pollen mother cells of Tradescantia as nuclear filaments.

Complete answer:
Haploid organisms are the organisms with a single pair of chromosomes while diploid organisms are defined as organisms having double pair of chromosomes.
During the gamete formation in the diploid organisms, the process of cell division through meiosis or reductional division occurs. This reduces the chromosome number in the gametes to half of the total chromosomes present in parents. In sexual reproduction, the male and female gametes fertilize and form zygote. So the process of fertilization restores the chromosome number in the organism.
Thus if the chromosome number in a diploid zygote is 40, then it means the diploid organism has 40 chromosomes in total and this will reduce to its half at the time of gamete formation through meiosis. Therefore, the chromosome number in a gamete will be 20.

So the correct answer is B. 20.

Additional information:
The process of meiosis has two phases- Meiosis-I and Meiosis-II with no interkinesis or of short period in which no replication occurs. Meiosis-I involves karyokinesis-I and cytokinesis-I while meiosis-II is similar to the mitosis process. It involves separation of genetically modified sister chromatids so brings haploidy in DNA amount while meiosis-I brings reduction in chromosome number only.

Note:
The cell division process occurs by two methods- mitosis and meiosis. Mitosis is involved in the asexual reproduction process while meiosis occurs at the time of gamete formation in sexual reproduction.