Question

In the XX–XO sex determination system, what does the 'O' represent?

Options

• A special chromosome named O

• The absence of a second sex chromosome

• An optional chromosome present in some cells

• An ovary-determining chromosome

Answer 1

In the XX–XO system found in grasshoppers and some insects, the 'O' denotes the absence of a second sex chromosome. Males have the XO genotype (one X chromosome and no corresponding partner), making them heterogametic and producing X and O-bearing sperm. Females have the XX genotype.