genic balance theory of sex determination
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The theory of genic balance given by Calvin Bridges (1926) states that instead of XY chromosomes, sex is determined by the genic balance or ratio between X-chromosomes and autosome genomes. ... It means that expression of maleness is not controlled by Y- chromosome but is instead localised on autosomes.
Information on Genic balance theory:-
➨ This theory was proposed by C.B. Bridges of sex determination in Drosophila.
➨ According to Bridges in Drosophila Y-chromosome is heterochromatic so it is not active in sex determination
➨ In Drosophila sex determination takes place by sex index ratio.
➨ Sex index ratio = Number of x Chromosomes(X)/Number of set of Autosomes(A).
➨ In Drosophila gene of femaleness is located on X-chromosome and gene or aieness is located on autosome.
➨ Gene of male fertility is located on y-chromosome.
➨ In Drosophila, y-chromosome plays additional role in spermatogenesis and development of male reproductive organ, so y-chromosome is essential for the production of fertile male.