Question

Which of the following is true about chromosomes?
A. Separate independent pieces responsible for variations is called a chromosome
B. Each cell will have two copies of each chromosome, one from each from the male and female parents.
C. Two germ cells combine to restore the normal number of chromosomes in the progeny
D. All of the above.

Answer 1

Chromosomes are the rod-shaped or filamentous, gene-bearing, a self-replicating nuclear component that contains nucleic acid and proteins in their structure and carries hereditary information, present in a definite number in a cell passing from the mother to daughter cell by division and parent to offsprings through reproduction.

Complete answer:
Each chromosome bears the hereditary information, which means a gene is encoded in each chromosome. So variation can be performed by a single chromosome.
Hence the statement of Option A is correct.
Each cell has two copies of a chromosome which means the diploid state. One set of a chromosome is obtained from the male parent and the other set of the chromosome is obtained from the female parent during the fertilization.
Hence the statement of option B is correct.

Germ cells are the only cells which contain the haploid chromosomes because it goes on to produce gametes which on fertilization gives rise to the progeny. And the progeny or the offspring will receive a diploid set of chromosomes.
Hence the statement in option C is correct.

As all the three statements are correct, hence option D. All of the above is the correct answer.

Note:
The chromosome contains chromatids, chromomere, primary constriction, centromere, secondary constriction, satellite, telomere in its structure. The secondary constriction is also known as NOR ( Nucleolar Organising Region ). In humans, $6$ chromosomes have the secondary constriction -$13,14,15,21,22$ and Y. Sat chromosomes are also known as marker chromosomes.