Biology · Principles of Inheritance and Variation · NEET
In XY type both sexes have the same total chromosomes: male is XY, female is XX (humans, Drosophila). In XO type there is no Y at all: the male has only one X (so an odd chromosome number) and the female has two X (grasshopper). In ZW type the pattern flips: the female is ZW and the male is ZZ (birds, some reptiles). In XY and XO the male makes two kinds of sperm, so the male decides sex. In ZW the female makes two kinds of eggs, so the female decides sex.
The grasshopper is the classic NEET example of XO type. The male has only one X chromosome plus the autosomes (no Y), and the female has a pair of X chromosomes plus autosomes. So the male makes two types of sperm: half carry an X and half carry no X. This appeared directly in NEET 2022 and NEET 2026.
Birds use the ZW type. Here the female is heterogametic: female is ZW and male is ZZ. Because the female makes two kinds of eggs (one with Z, one with W), the egg decides the sex of the chick. Do not confuse the letters: ZW just means the female carries two different sex chromosomes, the same idea as XY but on the female side.
Because the male grasshopper has only one X (XO) and the female has two X (XX), the male has one fewer chromosome. NEET 2026 used this: in a grasshopper population, members with 23 chromosomes are males (single X) and members with 24 chromosomes are females (two X). Remember: odd number = male, even number = female in XO type.
The grasshopper is male heterogametic. In XO type the male produces two different types of gametes (sperm with X or sperm without X), so the male is heterogametic and the female is homogametic. Female heterogamety belongs to the ZW type (birds), not to the grasshopper. NEET 2023 tested exactly this point.
Humans have XY type. The human male is 44 autosomes + XY and the female is 44 autosomes + XX. Both sexes have the same total of 46 chromosomes; only the sex chromosome pair differs. The father's sperm (X or Y) decides the child's sex, so the male is heterogametic in humans too.
XO type of sex determination can be found in
In a population of a grasshopper species, the chromosome number of some members is 23 and some other members possess 24 chromosomes. The 23 and 24 chromosome-bearing members in this species are ______.
Select the correct statement/s about sex determination in Grasshopper: A. It is female heterogamety. B. Male produces two types of gametes, with or without X chromosome. C. Total chromosome number is same in males and females. D. All eggs bear an additional X chromosome besides the autosomes.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Three: XY type (humans, Drosophila; male XY, female XX), XO type (grasshopper; male X, female XX), and ZW type (birds; female ZW, male ZZ). Learn one example for each.
No. In XY and ZW type the totals are equal. In XO type the male has one fewer chromosome because he lacks the second sex chromosome (only one X, no Y).
Because the male makes two different kinds of gametes: sperm carrying X and sperm carrying Y. The female makes only one kind (all eggs carry X). The kind that makes two types is heterogametic.
Yes. In ZW type the female is ZW (two different sex chromosomes) and the male is ZZ (two same). The female is heterogametic and decides the offspring's sex.
