A = ................ type of mechanism for sex-determination is found in insects like Drosophila melanogaster and mammals including human beings.

Options

A. A = XX-XY
B. A = XX-XO
C. A = ZW-ZZ
D. A = XY-XY

Explanation

**Step-by-Step Solution:**

1. **Identify the Mechanism of Sex Determination:**
The question asks for the type of mechanism for sex determination found in insects like Drosophila melanogaster and mammals, including humans.

2. **Understand the Chromosomal Basis:**
In Drosophila melanogaster (fruit flies) and humans, the sex determination is based on the presence of specific sex chromosomes. In these organisms, males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).

3. **Define Male Heterogamety:**
The term "male heterogamety" refers to the condition where males produce two different types of gametes concerning sex chromosomes. In this case, males produce gametes that can either carry an X chromosome or a Y chromosome.

4. **Summarize the Fusion of Gametes:**
When gametes fuse during fertilization, if an X gamete from the female fuses with an X gamete from the male, the result is a female (XX). If an X gamete from the female fuses with a Y gamete from the male, the result is a male (XY).

5. **Conclusion:**
Therefore, the type of mechanism for sex determination in Drosophila melanogaster and humans is termed "XY sex-determination system" or "male heterogamety."

**Final Answer:**
A = XY sex-determination system.

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