Question

In Drosophila the sex is determined by
A. Whether the egg is fertilized or determined parthenogenetically
B. The ratio of number of X chromosomes to set of autosomes
C. X and Y chromosomes
D. The ratio of pairs of X chromosomes to pairs of autosomes

Answer 1

Hint: Drosophila is a genus of two-winged flies that are used in evolutionary and developmental studies, commonly known as fruit flies. For the study of genetics and development, melanogaster is an important model organism.

Complete Answer:
- Drosophila is characterised by sexual dimorphism. Males can also easily be distinguished from females which have variations in size and colour.
- The female's length, however, is approx. Moreover, 2.5 mm, male is slightly smaller than female with darker dorsal sites of the male body due to a separate black patch at the abdomen.
- In our understanding of heredity, the sex chromosomes of the Drosophila melanogaster fruit fly have played a especially important role.
- Therefore, it can come as a surprise that a relatively unusual method for deciding sex is used by fruit flies. In Drosophila, sex is mainly determined by the X: A ratio, or the ratio of the number of X chromosomes to the number of autosomal sets (Cline & Meyer, 1996).
- The balance between encoded female-determining factors on the X chromosome and encoded male-determining factors on the autosomes decides the transcription sex-specific pattern will be initiated.
- Thus, females are XX, XXY, and XXYY flies, while males are XY and XO flies. With more than two copies of an X chromosome, flies are unable to survive because of the mechanism they use for dose compensation. Dosage compensation refers to the mechanisms by which animals equalise the amount of gene products in males and females derived from X-linked genes.
- Unlike in mammals, all of the Drosophila X chromosomes remain involved, and by doubling the expression of the X chromosome in males, flies change the levels of X-linked gene products.
- An additional copy of the X chromosome, containing approximately one-third of the fly genes, causes an aneuploid syndrome that substantially disrupts cell balance.

The Correct Answer is, option (B) "The ratio of the number of X chromosomes to the set of autosomes."

Note: Sex determination for Drosophila also varies in many other respects from mammalian sex determination. Second, at fertilisation, sex determination starts immediately, and there is no time of indifference. In addition, hormones are not liable for sex-specific traits; instead, the X: A ratio is sensed by each cell in the embryo, activating either the female or male-specific transcription pattern. Microarray studies show that the gender-specific distinctions in gene expression are very substantial. Approximately 30% of Drosophila genes have actually been shown to exhibit sex-specific biases in expression.