Q. 13.  In a certain taxon of insects some have 17 chromosomes and the other have 18 chromosomes. The 17 and 18 chromosome-bearing organiss are

a.  males and females, respectively

b.  females and males, respectively

c.  all males

d.  all females

(a).  In certain insects, such as cockroach, and some roundworms, the Y-chromosome is missing so that the male has only one sex chromosome, i.e., 'X'. The condition in the male is XO (O means absence of one sex chromosome) and in the female it is XX., All the other option given are wrong.