3. Cystic fibrosis is an autosomal recessive disorder in humans. What is the probability that an offspring will have cystic fibrosis if both parents heterozygous for cystic fibrosis? Enter your answer in the box, Your answer must be a whole number. square %

To determine the probability that an offspring will have cystic fibrosis if both parents are heterozygous for the disorder, we can use a Punnett square.<br /><br />Let's represent the alleles for cystic fibrosis as follows:<br />- N: Normal allele (dominant)<br />- n: Cystic fibrosis allele (recessive)<br /><br />Since both parents are heterozygous, their genotypes are Nn.<br /><br />Now, let's create a Punnett square to visualize the possible combinations of alleles in their offspring:<br /><br />| | N | n |<br />|-------|-----|-----|<br />| N | NN | Nn |<br />| n | Nn | nn |<br /><br />From the Punnett square, we can see that there are four possible combinations of alleles in the offspring:<br />1. NN (Normal)<br />2. Nn (Carrier)<br />3. Nn (Carrier)<br />4. nn (Affected with cystic fibrosis)<br /><br />Out of these four combinations, only one (nn) results in an offspring with cystic fibrosis.<br /><br />Therefore, the probability that an offspring will have cystic fibrosis if both parents are heterozygous for the disorder is 1 out of 4, or 25%.<br /><br />So, the answer is:<br />$\boxed{25\%}$