Question

question 2.cystic fibrosis is an autosomal recessive disorder in humans. what is the probability that an offspring will have cystic fibrosis if both parents are carriers of cystic fibrosis?a. 25%b. 50%c. 75%d. 100%

Explanation:

Step1: Define carrier genotype

Carriers are heterozygous: $Aa$ (where $a$ = recessive allele for cystic fibrosis, $A$ = dominant normal allele)

Step2: Set up Punnett square

Cross $Aa \times Aa$:

$$\begin{array}{c|cc} & A & a \\ \hline A & AA & Aa \\ a & Aa & aa \\ \end{array}$$

Step3: Calculate affected probability

Only $aa$ genotype causes cystic fibrosis. Probability = $\frac{\text{Number of } aa \text{ genotypes}}{\text{Total genotypes}} = \frac{1}{4} = 25\%$

Answer:

A. 25%