Karen and Steve each have a sibling with sickle-cell disease. Neither Karen nor Steve nor any of their parents have the disease, and none of them have been tested to see if they carry the sickle-cell allele. Based on this incomplete information, calculate the probability that if this couple has a child, the child will have sickle-cell disease.

Key Concepts

Sickle-Cell Disease Genetics

Sickle-cell disease is an autosomal recessive disorder caused by a mutation in the HBB gene, leading to abnormal hemoglobin. Individuals with two copies of the sickle-cell allele (homozygous recessive) exhibit the disease, while those with one copy (heterozygous) are carriers but do not show symptoms. Understanding this inheritance pattern is crucial for calculating the probability of offspring inheriting the disease.

Punnett Square

A Punnett square is a diagram used to predict the genetic makeup of offspring from two parents. It illustrates the possible combinations of alleles that can result from the mating of two individuals. By using a Punnett square, one can determine the likelihood of a child inheriting specific traits, such as sickle-cell disease, based on the genotypes of the parents.

Carrier Probability

In this scenario, since neither Karen nor Steve has sickle-cell disease, they could be carriers of the sickle-cell allele. The probability of them being carriers can be inferred from their siblings' conditions. If both siblings have sickle-cell disease, it suggests that both parents are likely carriers, which affects the probability of their child inheriting the disease. Understanding carrier status is essential for calculating the risk of the child having sickle-cell disease.