Read the passage and answer the following questions:
The initial clue about the genetic/chromosomal mechanism of sex determination can be traced back to some of the experiments carried out in insects. Henking (1891) could trace a specific nuclear structure all through spermatogenesis in a few insects, and it was also observed by him that 50 per cent of the sperm received this structure after spermatogenesis, whereas the other 50 per cent sperm did not receive it. Henking gave a name to this structure as the X body but he could not explain its significance. Further investigations by other scientists led to the conclusion that the 'X body' of Henking was in fact a chromosome and that is why it was given the name X-chromosome. 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.
According to the passage, what did Henking observe about the X body?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → After spermatogenesis, 50 per cent of the sperm received the X body and the other 50 per cent did not.
The passage states that Henking traced a nuclear structure all through spermatogenesis in a few insects, and that “50 per cent of the sperm received this structure after spermatogenesis, whereas the other 50 per cent sperm did not receive it.” He named it the X body. Later work showed it was a chromosome, the X-chromosome. So these insects make two kinds of sperm, with and without an X-chromosome.
Option (1) After spermatogenesis, 50 per cent of the sperm received the X body and the other 50 per cent did not. — Correct. This is Henking’s observation as given in the passage. Half the sperm had the X body and half did not, so the sperm were of two kinds.
Option (2) After spermatogenesis, all the sperm received the X body, but only half of the eggs did. — Incorrect. Henking studied spermatogenesis, not eggs. And the sperm did not all receive the X body; only half of them did.
Option (3) The X body was present in the sperm, and he explained it as the structure that decides the sex. — Incorrect. He named the structure the X body, but the passage says he could not explain its significance. Its role in sex determination came from the work of other scientists.
Option (4) After oogenesis, 50 per cent of the eggs received the X body and the other 50 per cent did not. — Incorrect. The structure was traced through spermatogenesis in males, not through oogenesis. The 50 : 50 split was among the sperm.