Assertion (A) : Birds like pigeon have heterogametic females whereas the males are homogametic.

Reason (R) : In pigeons, females have Z and W sex chromosomes whereas males have ZZ sex chromosomes.

The correct option is: Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

Step-by-step Explanation:

1. Understanding Sex Determination in Birds:
In birds, such as pigeons, sex determination is governed by the ZW sex-chromosomal system. This system is the opposite of the XY system found in humans and many other mammals.

2. Analyzing Assertion (A):
In the ZW system, the sex chromosomes are designated as Z and W. Females are the heterogametic sex because they produce two different kinds of gametes (ova)—one type carrying the Z chromosome and the other carrying the W chromosome. Males are the homogametic sex because they produce only one type of gamete (sperm), all containing a Z chromosome. Therefore, Assertion (A) is true.

3. Analyzing Reason (R):
The chromosomal makeup responsible for this difference is that female pigeons possess ZW sex chromosomes, while male pigeons possess ZZ sex chromosomes. Therefore, Reason (R) is also true.

4. Evaluating the Connection:
The reason females are heterogametic and males are homogametic (Assertion A) is precisely because females have different sex chromosomes (ZW) whereas males have the same sex chromosomes (ZZ) (Reason R). Thus, Reason (R) is the correct explanation of Assertion (A).