Question

A gene is composed of two alleles. An allele can be either dominant or recessive. Suppose that a husband and wife, who are both carriers of the sickle-cell anemia allele but do not have the disease, decide to have a child. Because both parents are carriers of the dise ase, each has one dominant normal-cell allele (S) and one recessive sickle-cell allele (s). Therefore, the genotype of each es one allele to his or her offspring with each allele being equally likely Complete parts a) through c) below a) Genes are always written with the dominant gene first. Therefore, there are two instances the offspring could have genotype (one if the mother contributes the dominant allele and the father contributes the non-dominant allele, and one if the father contributes the dominant allele and the mother contributes the non-dominant allele) List the other two possible genotypes of the offspring b) What is the probability that the offspring will have sickle-cell anemia? In other words, what is the probability that the offspring will have genotype ss? Interpret this probability The probability is 1/4. This means that there is a 25% chance that a randomly selected offspring will have sickle-cell anemia c) What is the probability that the offspring will not have sickle-cell anemia but will be a carrier (one normal-cell allele and one sickle-cell allele)? Interpret this probability The probability is _____. This means there is a _____ % chance that a randomly selected offspring will be a carrier, but will not have sickle-cell anemia.

Answer 1

Answer: If a husband and wife who are both carriers of the sickle-cell anemia allele (Ss) but do not have the disease decide to have a child, the offspring can be Normal (SS), carrier (Ss) or sick (ss) with the probability ¼, 2/4 (½) and ¼ respectively.

Explanation: If the mother contributes the dominant allele and the father also contributes the dominant allele, the genotype of the child will be SS. The probability is ¼. This means there is a 25% chance that a randomly selected offspring will be a normal child and will not have sickle-cell anemia.

If the mother contributes the dominant allele and the father contributes the recessive allele, the genotype of the child will be Ss. The probability is 2/4 or ½. This means there is a 50% chance that a randomly selected offspring will be a carrier of sickle cell anemia, but will not have sickle-cell anemia.

If the mother contributes the recessive allele and the father also contributes the recessive allele, the genotype of the child will be ss. The probability is ¼. This means there is a 25% chance that a randomly selected offspring will have sickle cell anemia.

Check attached image for illustrations.