24. In humans, XX males and XY females are rare, such rare sexes are due to
(1) Deletion of X chromosome
(2) Deletion of Y chromosome
(3) XY translocation
(4) Duplication of X chromosomes

Concept

• Normal males: 46,XY with SRY gene on the Y → testis development.

• Normal females: 46,XX without SRY → ovary development.

• XX males typically have SRY translocated from Y to X, so an X chromosome carries SRY and triggers male development despite the XX set.

• XY females can result when the Y chromosome lacks functional SRY (e.g., deletion or translocation that removes SRY), so an XY embryo develops as female.

This pattern is best explained by an X–Y translocation involving the SRY region.

Option‑wise explanation

1. Deletion of X chromosome

   • Would give Turner-type monosomy (XO) or structural X defects, not specifically XX males or XY females.

2. Deletion of Y chromosome

   • Complete loss of Y is usually lethal or yields XO‑like females; it doesn’t explain XX males (who have no Y but are male because of SRY on X).

3. XY translocation – correct

   • Mis‑exchange between X and Y, especially involving the SRY locus, can:

     • Move SRY onto an X → 46,XX male.

     • Remove SRY from a Y → 46,XY female.

   • This exactly matches the “rare XX males and XY females” described.

4. Duplication of X chromosomes

   • Extra X (e.g., XXY in Klinefelter) affects gonadal function but still usually gives a male with a Y; it does not create XX males without Y or XY females without proper SRY.

So, rare XX males and XY females are best explained by X–Y translocation (option 3).