Describe the Genic Balance Theory of sex determination.

Explanation

Genic balance theory of sex determination was proposed by Calvin Bridges with reference to sex determination in Drosophila. He proposed, that both the X-chromosomes and autosomes. together play a role in sex determination in Drosophila, where as Y-chromosome has no role. This theory explains that genes for maleness are located on autosome and for femaleness on X - chromosome in Drosophila. Y-chromosome in lacks male - determining factor but contains gametic information essential to male fertility . Sex in Drosophila is determined by ratio of X-chromosome to the number of haploid sets of autosomes.
Sex ratio `= ("No. of X-chromosomes")/("No. of sets of autosomes")`
The chromosomal complement, X/A ratio and sex of Drosophila are tabulated below.