Correct option is B
The question involves a temperature-sensitive recessive mutation in Drosophila, where the male carries the mutation on his X chromosome. This mutation is lethal at 29°C but viable at 18°C. This means that when eggs are reared at 29°C, any male offspring inheriting the mutant X chromosome will die due to the temperature-sensitive lethality. Females, on the other hand, will survive as they have two X chromosomes and thus can carry one normal X chromosome. The outcome of the mating depends on whether the female carries the normal X chromosome or the attached X chromosome (an X chromosome that is genetically modified or linked).
Explanation for the Two Cases:
Case A: Mating with a normal female
-The male has the X-linked lethal mutation and is passed on to the female progeny (if the offspring inherits the X chromosome from the father).
-The males inheriting the mutant X chromosome will die at 29°C due to the temperature-sensitive mutation.
-Therefore, in this case, the ratio of males to females will be 1:1 because all females will survive and males carrying the mutation will not.
Case B: Mating with a female containing attached X-chromosome
In this scenario, the X chromosome is attached, which may result in only female progeny, as males do not receive the female's X chromosome. Hence, no male progeny will survive, and only females will be produced.
Important Key Points:
X-linked recessive mutation: This mutation is on the X chromosome, meaning males only have one X chromosome, which they inherit from the mother, making them more susceptible to the mutation.
Temperature-sensitive lethality: The mutation is lethal at 29°C, meaning it affects the development of the organism only at that specific temperature.
Mating with a normal female (Case A): In this case, the male progeny that inherit the X chromosome with the mutation will die, leaving a 1:1 ratio of surviving females and dead males.
Mating with a female containing attached X-chromosome (Case B): This results in only female progeny, as the male progeny die, and only females survive due to the absence of the Y chromosome.
