Question

Analyse the following two cases of sex determination in different organisms:
Case I: Males have (XO) sex chromosomes and females have two copies of same sex chromosome (XX).
Case II: Females have two different sex chromosomes (ZW) and males have two copies of same sex chromosome (ZZ).
Identify the type of heterogamety in each case, giving one example of each.

Hint:

In humans and Drosophila, it is Male Heterogamety (XY).
In birds, it is exactly the opposite (Female is ZW).

Answer 1

Step 1: Understanding the Concept:
Heterogamety refers to the production of two different types of gametes by one sex regarding the sex chromosomes.
Step 2: Detailed Explanation:
Case I (XX-XO):
- Females (XX) produce only one type of gamete (X).
- Males (XO) produce two types of gametes: 50\% with an X chromosome and 50\% with no sex chromosome (O).
- This is Male Heterogamety.
- Example: Grasshopper or Roundworms.
Case II (ZZ-ZW):
- Males (ZZ) produce only one type of gamete (Z).
- Females (ZW) produce two types of gametes: 50\% with a Z chromosome and 50\% with a W chromosome.
- This is Female Heterogamety.
- Example: Birds (e.g., Fowl) or Butterflies.
Step 3: Final Answer:
Case I: Male heterogamety (Grasshopper).
Case II: Female heterogamety (Birds).