In humans, the ABO blood type is under the control of autosomal multiple alleles. Color blindness is a recessive X-linked trait. If two parents who are both type A and have normal vision produce a son who is color-blind and is type O, what is the probability that their next child will be a female who has normal vision and is type O?

Verified step by step guidance

1. Identify the genotypes of the parents for both traits. Since both parents are type A, they could be either homozygous (IAIA) or heterozygous (IAi) for the ABO blood type. For normal vision, they must have at least one normal vision allele (XNXn or XNXN).
2. Determine the possible genotypes of the son. Since the son is type O, he must have inherited the 'i' allele from both parents, indicating both parents are heterozygous (IAi). For color blindness, the son must have inherited the X-linked recessive allele (Xn) from his mother, indicating she is a carrier (XNXn).
3. Calculate the probability of the next child being type O. Since both parents are IAi, the probability of having a child with type O blood (ii) is 1/4.
4. Calculate the probability of the next child being female and having normal vision. The probability of having a female child is 1/2. The probability of a female child having normal vision (XNXN or XNXn) is 3/4, since the mother is a carrier (XNXn) and the father has normal vision (XNY).
5. Combine the probabilities. Multiply the probability of the child being type O (1/4) by the probability of being female (1/2) and having normal vision (3/4) to find the overall probability.

Key Concepts

ABO Blood Type Genetics

The ABO blood type system is determined by multiple alleles (IA, IB, and i) at a single locus on an autosome. Individuals can have blood types A, B, AB, or O depending on the combination of alleles inherited from their parents. Type O results from the presence of two i alleles, while type A can arise from either IAIA or IAi genotypes.

X-linked Inheritance

X-linked traits are associated with genes located on the X chromosome. In humans, males have one X and one Y chromosome, while females have two X chromosomes. Color blindness is a recessive trait linked to the X chromosome, meaning that males only need one copy of the allele to express the trait, while females need two copies.

Punnett Squares and Probability

Punnett squares are tools used to predict the genetic outcomes of offspring based on the alleles of the parents. By determining the possible combinations of alleles from each parent, one can calculate the probabilities of various traits in the offspring. This method is essential for understanding inheritance patterns, especially in cases involving multiple alleles and X-linked traits.