Question

Which one of the following conditions correctly describes the manner of determining the sex in the given example?
A) Homozygous sex chromosomes (ZZ) determine female sex in birds.
B) XO type of sex chromosomes determine male sex in grasshopper.
C) XO Condition in human as found in Turner Syndrome, determines female sex.
D) Homozygous sex chromosomes (XX) produce male in Dorsophila.

Answer 1

Homozygous is a distinct genetic condition where from both parents the individual offspring inherits the same alleles for a particular gene. While in heterozygous, the offspring inherits different forms of a particular gene. When one or two or more genes occur alternatively at a given site on a chromosome, it is called allele.

Complete answer:
1. We find ZW-ZZ sex determination in birds where females have heteromorphic (ZW) and males have homomorphic (ZZ) sex chromosomes. So, the first option can’t happen.
2. In humans we can see the males are heterogametic and thus they carry XY chromosomes but the female, being homogametic, carries XX chromosomes. In human females, if the part or full copy of one X Chromosome is absent, then this problem is called ‘Turner Syndrome’. But, for determining the female sex, the XO condition can’t be applied.
3. In regards to Drosophila, the ratio of the total number of X chromosomes to that of the complete set of autosomes as placed in the denominator makes the ratio. Here the proportionate value is less than one for a normal male. And, thus we can’t say that in Dorsophila, the Homozygous sex chromosomes produce males.
4. In various roundworms and grasshoppers, XX-XO mechanism of sex determination is present where we can see that females are homogametic, that is, XX, but the male carries only one sex chromosome (XO). That is why, it is correct that XO type of sex chromosomes determine male sex in terms of grasshopper.

Note: Male grasshoppers produce two different types of gametes. So, they are called heterogametic sex. As Male grasshoppers have only one sex chromosome, so it is considered that they have XO chromosomes.