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.
In insects, eggs fertilised by sperm having an _________ become females.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → X-chromosome
In the XO type of sex determination, all eggs carry one X chromosome. Some sperms carry an X chromosome, and some do not. An egg fertilised by a sperm with an X chromosome becomes a female. One fertilised by a sperm without it becomes a male.
(1) X-chromosome — Correct. Egg and sperm both give an X, so the offspring is XX, a female.
(2) Y-chromosome — Incorrect. There is no Y chromosome in this type of insect.
(3) W-chromosome — Incorrect. The W chromosome belongs to the ZW type of birds, where it is carried by the female.
(4) Z-chromosome — Incorrect. The Z chromosome also belongs to the ZW type of birds.
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 – …
