Q. 13

In a certain taxon of insects some have 17 chromosomes and the others have 18 chromosomes. The 17 and 18 chromosome-bearing organisms are:
A. males and females, respectively

B. females and males, respectively

C. all males

D. all females

Answer :

The 17 and 18 chromosome-bearing organisms are males and females, respectively. Because the sex determination in this taxon of insects is of male heterogamety with XO type. This means females have their eggs bearing an additional X chromosome besides autosomes. And males have their sperms bearing an X chromosome whereas some do not. Example : Grasshopper.


Therefore sperm without an X chromosome will have chromosome number to be one less than that of the females of same species. In this case males have 17 autosomes and females have 17 autosomes and one X chromosome.

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