Question

Genic balance theory of sex was proposed by
A) Bridges
B) Bateson
C) Boveri
D) Moore

Answer 1

As per the genetic balance theory of sex, sex is determined by the geneic balance between X-chromosomes and the autosome genomes instead of XY chromsosomes. The theory is applicable to Drosophila melanogaster.

Complete answer:
Let us analyse the options and find the correct answer.

Option A: Genic balance theory of sex was given by Calvin Bridges. Therefore, this is the correct option.
It states that instead of $XY$ chromosomes, sex is determined by the genic balance or ratio between X-chromosome and autosome genomes.
Drosophila has eight chromosomes ($n = 4$), three pairs of autosomes and one pair of sex chromosomes.
In Drosophila the sex determination is achieved by a balance of female determinants on the X chromosome (X) and male determinants on the autosomes (A). This type of sex determination is called genic balance theory.
Calvin Bridges genic balance theory observations are:
Sex is determined by $\dfrac{X}{A}$ ratio- If the ratio is $10$ the offspring’s develop into female (Example:$2A + XX{\text{ }}or{\text{ }}3A + XXX$).
If it is $0.5$, then offspring develops into male (Example:$2A + XY$).
If it is between$0.5-1$, the offspring will neither male nor female.
Super females have a ratio of $1.5$ (Example:$2A + XXX$).
Super male have a ratio of $0.33$.
Option B: William Bateson is known as the father of modern genetics and he was the first person to use the word ‘genetics’ to describe the study of heredity. Therefore, this is the incorrect option.
Option C: Theodor Boveri gave proposed the law of constant chromosome and not the genic balance theory of sex. Therefore, this is the incorrect option.
Option D: Moore was involved in the field of neurochemistry and also in the study of sickle cell anaemia. Therefore, this is the incorrect option.

Thus, the correct answer is option (A) bridges.

Note: This theory also explains the reason for the occurrence of sexual variants in the first fly population such as inter-sex, Meta males and Meta females apart from normal male and female.Bridges findings suggested that in Drosophila male development factors are localized on autosomes. The X- chromosomes perhaps carries some female determining genes Example: Sxl.