XO Type Sex Determination — NEET Biology
✅ Asked in NEET 2026It was also observed that in a large number of insects the mechanism of sex determination is of the XO type, i.e., all eggs bear an additional X-chromosome besides the other chromosomes (autosomes). On the other hand, some of the sperms bear the X-chromosome whereas some do not. Eggs fertilised by sperm having an X-chromosome become females and, those fertilised by sperms that do not have an X-chromosome become males. Do you think the number of chromosomes in the male and female are equal? Due to the involvement of the X-chromosome in the determination of sex, it was designated to be the sex chromosome, and the rest of the chromosomes were named as autosomes.Grasshopper is an example of XO type of sex determination in which the males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes.
In XO sex determination (like grasshoppers), females have two X-chromosomes (XX) while males have only one X-chromosome (XO)—no second sex chromosome. Males are heterogametic and produce two types of sperm: those carrying X and those with no sex chromosome. Females are homogametic, producing only X-bearing eggs. The key trap: students confuse which sex is heterogametic and incorrectly assume males have XY instead of XO. Remember: XO means males lack a second sex chromosome entirely, making the total chromosome count unequal between sexes. NTA tests this because it requires understanding gamete types and sex determination mechanisms—fundamental to inheritance patterns tested repeatedly in NEET.
This paragraph was tested 2 times in NEET.
In a grasshopper population some members have 23 chromosomes and some have 24. The 23 and 24 chromosome members respectively are
Select the correct statement(s) with respect to the mechanism of sex determination in Grasshopper. (A) It is an example of female heterogamety. (B) Male produces two different types of gametes either with or without X chromosome. (C) Total number of chromosomes (autosomes and sex chromosomes) is same in both males and females. (D) All eggs bear an additional X chromosome besides the autosomes. (NEET 2022)
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