Problem 2 - Campbell Biology

Question

A man with type A blood marries a woman with type \(\mathrm{B}\) blood. Their child has type O blood. What are the genotypes of these three individuals? What genotypes, and in what frequencies, would you expect in future offspring from this marriage?

Step-by-Step Solution

Answer

The man is AO, the woman is BO, and the child is OO. Future offspring frequencies: 25% AO, 25% BO, 25% AB, 25% OO.

Step 1 - Determine the possible genotypes for blood types

Blood type A can have two possible genotypes: AO or AA. Blood type B can have two possible genotypes: BO or BB. Blood type O has one genotype: OO.

Step 2 - Analyze the child's genotype

Since the child has type O blood, the child's genotype is OO. This means the child inherited one O allele from each parent.

Step 3 - Determine the parents' genotypes

Because the child inherited an O allele from each parent, both parents must carry an O allele. Therefore, the man with type A blood must have the genotype AO, and the woman with type B blood must have the genotype BO.

Step 4 - Predict the genotypes and frequencies of future offspring

Use a Punnett square to find the possible genotypes for future offspring. The father (AO) and the mother (BO) can each contribute an A, B, or O allele.- Possible genotypes: AO, BO, AB, OO.- Expected frequencies: - AO (type A): 25% - BO (type B): 25% - AB (type AB): 25% - OO (type O): 25%

Key Concepts

Genotype

A genotype represents the genetic makeup of an individual. It consists of the specific alleles (versions of a gene) inherited from both parents. In the context of blood types, the genotype will determine the blood type. For example, if someone has type A blood, they could have the genotype AA or AO. Each genotype combination results from the alleles received from the parents.

Punnett Square

A Punnett square is a simple graphical way to predict the possible genotypes of offspring based on the genotypes of the parents. In our exercise, we use a Punnett square to find the genetic combinations of children born to a man with genotype AO and a woman with genotype BO. Each box in the square shows a possible genotype for their child. The combinations are: AO, BO, AB, and OO. This method helps us understand inheritance patterns and the probability of each genotype occurring.

Alleles

Alleles are different forms of a gene. Each individual inherits two alleles for each gene, one from each parent. For blood types, the main alleles are A, B, and O. The combination of these alleles determines a person's blood type. For instance, a person with allele A from one parent and allele O from the other would have type A blood. Understanding alleles is crucial for grasping how traits are passed from parents to offspring.

Blood Types

Blood types are determined by specific combinations of alleles. There are four main blood types: A, B, AB, and O. Each type is the result of different genetic combinations:

• Type A: AA or AO
• Type B: BB or BO
• Type AB: AB
• Type O: OO

The exercise illustrates how two parents with type A and type B blood can have children with blood types A, B, AB, or O. This thorough understanding of blood types and their genetic basis demonstrates the complexity of inheritance.