Principles of Inheritance and Variation Question 53
53. The salivary gland chromosomes in the dipteran larvae, are useful in gene mapping because:
(a) these are fused
(b) these are much longer in size
(c) these are easy to stain
(d) They have endoreduplicated chromosomes.
Show Answer
Answer : d
Hints & Solution
(d) Polytene chromosomes were first reported by EG Balbiani in 1881. They are quite common in salivary glands of insects and are therefore popularly called salivary gland chromosomes. Polytene chromosomes also occur in other organs of insects, antipodal cells (of embryo sac), endosperm cells and suspensor cell of embryo. The chromosomes can reach length of $200 \mu m$ and contain 1000 to 16000 times DNA as compared to the ordinary somatic chromosomes. The giant chromosomes are formed by somatic pairing between homologous chromosomes, and repeated replication (endomitosis) of their chromatids.
