Question

Drosophila is metamale with the chromosomal formulation.
A. \[2A + 3X\]
B. $3A + 3X$
C. $4A + 3X$
D. $3A + XY$
E. $2A + XY$

Answer 1

Hint:-A metamale is a low viability Drosophila fruit fly. Two types of chromosomes are present. They are autosomes and sex chromosomes. There are two types of sex chromosomes- X and Y.

Complete answer:
In the case of Drosophila, XX codes for females and XY is for males. But the mechanism of sex determination is different from that of the mammals. In the case of mammals, the chromosome Y determines maleness. In the case of Drosophila, chromosome Y is not involved in the determination of sex. Rather than that, the genes present on the Y chromosome plays an important role in sperm formation but not in sex determination. Calvin Bridges in the year 1921 stated that the sex in Drosophila is determined by the balance of autosomal alleles that favour maleness and alleles on X- a chromosome that favour femaleness. According to him, the ratio of X- chromosomes to autosomal sets determines the sex of Drosophila. The factors that are responsible for maleness are not present in the sex chromosome but are present on the autosomal chromosomes. X-chromosome contains the genes for some female determining factors. A sex switch gene directs the female development. The gene responsible for this is called the sex lethal (Sxl) gene that is present on the X-chromosome. Activation of the Sxl gene relies on a ratio of X- chromosomes to a set of autosomes. The Y- chromosome of the male determines male fertility.
\[2A + 3X\]- This formula shows that there are two sets of autosomes and three X chromosomes present. This will give a total of 9 chromosomes and the ratio will be 1.5. This will give rise to meta females.
$3A + 3X$- This shows the presence of three sets of autosomal chromosomes and three X chromosomes. The ratio will be 1. This will give females.
$4A + 3X$- There is a presence of 4 sets of autosomal chromosomes and 3 X chromosomes.
$3A + XY$- There is a presence of three sets of autosomes and one X and one Y chromosome. The ratio will be 0.33. This will be a meta male.
$2A + XY$- There is a presence of two sets of autosomes and one X chromosome and one Y chromosome. This will give a ratio of 0.50 and this will be a male.

Drosophila is metamale with chromosomal formulation$3A + XY$. So, the correct answer is option C.

Note:- There is one more type of chromosome that is gynandromorph Drosophila. It contains both male and female characteristics. In some cases, it is bilaterally symmetrical where one half is male and the other half is female.