Question

According to genic balance theory of Bridges $\dfrac{X}{A} = 1.5$ will make the individual:
a. Male
b. Female
c. Intersex
d. Super female

Answer 1

The establishment of male and female individuals or male and female organs of an individual is called sex determination. The Genic balance theory of Sex was propounded by Bridges in 1926 and is based on his work on Drosophila.

Complete answer:
According to the genic balance theory, sex is determined by the balance or ration between number of X-chromosomes and autosome genomes.

$\dfrac{2X}{2A}$ or 1 produces fertile females, higher ratios (i.e. 1.5) infertile meta-females. O.5 as functional males, and ratio between 0.5 and 1.0 as intersex while a ratio between 0.5 produces infertile Meta males.

The genotype XXY + 2A produces female phenotype in Drosophila.

Hence, the correct answer is option (D).

Additional information:
The sex determination in animals is of three types:

Environmental determination of sex- It occurs in some hermaphrodite animals. For example, marine mollusk Crepidula becomes female when reared alone but produces male in company of an adult female.

Genetic determination of sex- In this, the sex determination is controlled by fertility factor located on a plasmid, for example in bacteria. In some simple organisms like Chlamydomonas, sex is determined by a single gene.

Chromosomal determination of sex- In most animals and some plants, sex is determined by sex chromosomes or allosomes. For example, sex determination in mammals and many insects with females having homomorphic XX chromosomes and males possessing heteromorphic XY chromosomes. In this type sex is determines at the time of fertilization and it is known as syngametic sex determination.

Note: Bridges and T.H. Morgan was the first to experimentally prove that genes are located on the chromosomes. They worked independently and the evidence came from two sets of experiments performed by them.