An albino girl gets married to a normal boy. What are the chances of their having an affected child and what are the chances of their children being carriers ?
**Core Concept:** Genetic Disorders, Dominant and Recessive Genes, Punnett Squares
An albino girl (homozygous for a recessive allele) gets married to a normal boy (homozygous for a dominant allele). Punnett squares, which are useful visual aids in understanding gene inheritance patterns, can be used to determine the probability of different outcomes in their offspring.
**Why the Correct Answer is Right:**
Let's consider the following Punnett Square:
```plaintext
A A (Albino Girl) | A a (Normal Boy)
________________|_______________
A A | A a
----------------------+----------------------
A a | a A
----------------------+----------------------
a a | a A
```
In this Punnett Square, there are four possible combinations of offspring: AA (Albino), Aa (Albinism), aA (Normal), and aa (Normal).
1. AA (Albino) Offspring: In this case, both parents are carriers (heterozygous) for the recessive allele. Since the girl is homozygous (AA), there is a 25% chance of this offspring being affected (AA).
2. Aa (Albinism) Offspring: In this case, one parent is a carrier (Aa) and the other is homozygous (AA). There is a 50% chance of this offspring being affected (Aa) and a 50% chance of being a carrier (Aa).
3. aA (Normal) Offspring: In this case, one parent is a carrier (Aa) and the other is homozygous (AA). There is a 50% chance of this offspring being affected (Aa) and a 50% chance of being a carrier (Aa).
4. aa (Normal) Offspring: In this case, both parents are carriers (Aa). There is a 50% chance of this offspring being affected (Aa) and a 50% chance of being a carrier (Aa).
**Why Each Wrong Answer is Wrong:**
1. **Option A (AA):** This option is incorrect because one parent is homozygous (AA) and the other is heterozygous (Aa). The offspring will be affected with albinism (AA) only when both parents are homozygous for the recessive allele.
2. **Option B (Aa):** This option is incorrect because the offspring will be affected (Aa) only when both parents are heterozygous for the recessive allele. In this case, one parent is homozygous (AA) and the other is heterozygous (Aa).
3. **Option C (aa):** This option is incorrect because the offspring will be affected (Aa) only when one parent is homozygous (AA) and the other is heterozygous (Aa). In this case, one parent is homozygous (AA) and