Question

Describe the genetic balance balance theory of sex determination.

Answer 1

Hint: The genic balance system of sex determination also explains the reasons for occuuence of sexual varients in the fruit fly population such as inter–sex, metamales, metafemales part from normal male and female individual.

Complete step-by-step answer:
living organisms, with a very few exceptions, are differentiated into male and female individuals based on their morphological, physiological and behavioural characteristics. The biological system which determines the development of sexual characteristics in an organism is called sex –determination. The two different types of sex –determination systems are:
> Chromosomal sex determination.
> Non –genetic sex determination.
In chromosomal sex determination, the individuals will process specialixed chromosomes called sex chromosomes. In this case, the presence or absence of a particular sex chromosomes or the relative ratio of these sex chromosomes determines the sex of the individuals. Drosophila melanogaster (fruit flies) shows XX female and XY male sex chromosomal constitution which is similar to the human beings. The mechanism of sex determination is quite different in Drosophila from humans. In humans beings , the Y chromose have a role in determining the sex of individuals, Drosophila has eight chromosomes (n = 4), three pairs of autosomes and one pair of sex chromosomes. The sex in Drosophila is determined by the ratio of number of X chromosomes to that of the number of sets of autosomes.

Note: The theory of genic balance ( sex determination ) is given by Calvin Bridges in the year 1926 which states that, sex is determined by the genic balance or ratio between X–chromosome and autosome genomoes instead of XY chromosomes. Living Even though the mechanism greatly varies, the sexes of the individuals are genetically determined.