Sex Determination
Read the following passage carefully and answer the given questions.
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. Sex determining mechanism in case of humans is XY type. A pair of X-chromosomes are present in the female, whereas the presence of an X and Y chromosome are determinant of the male characteristic. During spermatogenesis among males, two types of gametes are produced. 50 per cent of the total sperm produced carry the X-chromosome and the rest 50 per cent has Y-chromosome besides the autosomes. Females, however, produce only one type of ovum with an X-chromosome. There is an equal probability of fertilisation of the ovum with the sperm carrying either X or Y chromosome. The sex determination in honey bee is based on the number of sets of chromosomes which is an individual receives. An offspring formed from the union of a sperm and an egg develops as a female (queen or worker), and an unfertilised egg develops as a male (drone) by means of parthenogenesis.
Insects are an example of ______ type of sex determination.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → XO
In a large number of insects, sex is decided by the XO type of mechanism. All eggs carry one X chromosome. Some sperms carry an X chromosome and some carry none. An egg fertilised by a sperm with an X chromosome becomes a female (XX), and one fertilised by a sperm without it becomes a male (XO). The grasshopper is an example.
(1) XO — Correct. This is the type found in insects.
(2) XY — Incorrect. This is the type found in humans, where the male has an X and a Y chromosome.
(3) XX — Incorrect. This is only the pair of sex chromosomes of a female. It is not a type of mechanism.
(4) YO — Incorrect. No such type exists.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Sex Determination – …
