Question

A female fruit fly heterozygous for sex-linked genes is mated with normal male fruit fly. The male specific chromosome will enter the egg cell in proportion of
A. 1:1
B. 2:1
C. 3:1
D. 7:1

Answer 1

Hint: Chromosomes are thread-like structures located inside the nucleus in plant and animal cells. These carry the genetic information of an individual. Chromosomes inherited in an individual in the form of autosomes and sex chromosomes. Autosomes are chromosomes that describe the character trait of an organism. Sex chromosomes are chromosomes that define the sex of an individual.

Step by step answer:Most of the animals show sexual dimorphism, i.e., an individual organism is either a male or a female. In dimorphic animals, sex is determined by the sex chromosomes. Such organisms have one pair of sex chromosomes and other pairs as autosomes. The female drosophila has two X chromosomes (XX) and male drosophila has one X and one Y chromosome (XY). The Y chromosome is shorter than the X chromosome. At meiosis in females, the two X chromosomes pair and segregate like autosomes and each egg receives one X chromosome. In males, the X and Y chromosomes pair and segregate so that one sperm cell receives the X chromosome and the other receives the Y chromosome. The female drosophila is thus said as homogametic sex and male drosophila is known as heterogametic sex. These chromosomes are produced in equal amounts and are inherited in equal proportions.
Hence, the correct option is A. 1:1

Note: In Drosophila, Y chromosome does not play an important role in sex determination. It plays important role in sperm production in males but not in sex determination. Sex in drosophila is determined by the balance ratio of autosomal alleles that favors maleness and alleles present on X chromosomes favors femaleness.