Question

Genic balance theory for sex determination in drosophila was proposed by
A. Pro. R. P. Roy
B. H. E. Warmke
C. C. B. Bridges
D. McClung

Answer 1

Hint: Genic Balance was a theory which explains the sexuality of fruit fly- Drosophila melanogaster. This theory explains the sex of the fruit fly based on the X to A ratio. The scientist, who discovered it, was a part of the “Fly Room” at Columbia University.

Complete answer:
-The living organisms are differentiated into two main types of sexes i.e. male and female (except other sexualities).
-Scientific studies found that specific chromosomes are responsible for the development of physical and behavioural sexual characteristics in an organism.
-The biological mechanism that determines the development of sexual characteristics is called- sex determination.
-In Chromosomal sex determination, the sex of an individual is determined by the presence of a particular sex chromosome or the ratio of these chromosomes in the individual.
-For example, in humans, the chromosome XX will result in the development of female characteristics while the presence of the XY chromosome will lead to the development of male characteristics. Hence here, the presence of one Y chromosome will result in the development of male features irrespective of the number of X chromosomes present (XY and XXXY both are going to show the male characters). But in Drosophila, this is not the case. Drosophila has got eight chromosomes, i.e. four pairs of chromosomes. -Three pairs of chromosomes are autosomes while one pair of the chromosome is the sex chromosome.
-But the interesting fact is, the presence of Y chromosome here, does determine the sex of the fly.
-The sex determination in fruit flies is done by taking the ratio of X chromosomes to the number of autosomes i.e. X/A ratio.
-This type of sex determination is called Genic Balance System and this system was proposed by a scientist- Calvin Bridges in $1926$ .

Hence, the correct answer is option (C).

Note: As the ratio of X chromosome to the number of autosomes determine the sex of the fly, when the ratio is $1$ , the sex will be female, when the ratio comes out to be $0.5$ , the sex will be male. If the ratio is between $1$ and $0.5$ , the individual will be intersex, if the ratio is greater than one, the individual will be metafemale and if the ratio is less than $0.5$, the individual will be metamale.