Question

Cystic fibrosis is a genetic disorder that damages the tissues of the lungs. A - normal lung function, a - afflicted with Cystic fibrosis

Which 2 crosses below would result in a child expressing this condition?

Responses

Aa x AA
Aa x AA

Aa x Aa

Aa x Aa

aa x AA
aa x AA

AA x AA
AA x AA

aa x aa

Answer 1

Cystic fibrosis is a recessive genetic disorder, which means that an individual must have two copies of the recessive allele (aa) to express the condition.

In this scenario, the letters used denote:
- A = normal allele
- a = cystic fibrosis allele

To determine which crosses would result in a child expressing cystic fibrosis (aa), we need to look for crosses that could produce the aa genotype.

The following crosses are relevant to producing an affected child (aa):

1. **Aa x Aa**
- Possible genotypes of the offspring: AA, Aa, Aa, aa
- This cross can produce 1 aa offspring (25% chance).

2. **aa x AA**
- Possible genotypes of the offspring: Aa, Aa, Aa, Aa
- This cross cannot produce any aa offspring (0% chance).

3. **AA x AA**
- Possible genotypes of the offspring: AA, AA, AA, AA
- This cross cannot produce any aa offspring (0% chance).

4. **aa x aa**
- Possible genotypes of the offspring: aa, aa, aa, aa
- This cross will always produce aa offspring (100% chance).

So, the crosses that would result in a child expressing cystic fibrosis (aa) are:

- **Aa x Aa**
- **aa x aa**

Thus, the correct responses that would result in a child expressing cystic fibrosis are:
1. **Aa x Aa**
2. **aa x aa**