Sex Determination

Step 1: In humans and many other organisms, the XX–XY system shows male heterogamety where males produce two types of gametes (X and Y), so Assertion (A) is true.
Step 2: However, in birds, females are the heterogametic sex (ZW), and males are homogametic (ZZ), making Reason (R) false.
Step 3: Since (R) is incorrect, it cannot explain (A).
Thus, (A) is true, but (R) is false.

Step 1: Understanding the mechanism of sex determination in honey-bees:
- In honey-bees, sex determination follows a haplodiploid system.
- Males (drones) are haploid, meaning they have only one set of chromosomes (half the number of chromosomes as females).
- Females (workers and queens) are diploid, meaning they have two sets of chromosomes (32 chromosomes in this case).
Step 2: Analyzing the given statements:
- Statement (i): "A zygote formed from the union of a sperm and an egg develops into a male."
This statement is incorrect because a male bee (drone) develops from an unfertilized egg (haploid), not from the union of sperm and egg. The fertilized egg results in a female.
- Statement (ii): "Males have half the number of chromosomes as that of females."
This statement is correct. Males are haploid, so they have half the number of chromosomes compared to the diploid females.
- Statement (iii): "The females are diploid having 32 chromosomes." This statement is correct. Females (workers and queens) are diploid and have 32 chromosomes.
- Statement (iv): "Males have a father and can produce sons." This statement is correct. Males (drones) are produced from unfertilized eggs and have a father (the queen). They can mate with females (queens) to produce sons.
Step 3: Conclusion:
The correct statements are (ii) and (iv). Thus, the correct answer is option (D).