Question

List all possible genotypes for the \(\mathrm{A}, \mathrm{B}, \mathrm{AB},\) and \(\mathrm{O}\) phenotypes. Is the mode of inheritance of the \(\mathrm{ABO}\) blood types representative of dominance, recessiveness, or codominance?

Short answer

Question: What is the mode of inheritance for the ABO blood types, and list the genotypes for each blood type. Answer: The mode of inheritance for the ABO blood types is codominance. The genotypes for each blood type are as follows: - Blood type A: IAIA or IAi - Blood type B: IBIB or IBi - Blood type AB: IAIB - Blood type O: ii

Step-by-step solution

Understand the ABO blood group system

The ABO blood group system classifies human blood into A, B, AB, and O types, based on the antigens present on the surface of red blood cells. There are three different alleles for blood types: IA, IB, and i. The IA and IB alleles are codominant, meaning that they both express themselves when paired together. The i allele is recessive to both IA and IB.

List the genotypes for blood type A

Blood type A can have two genotypes: IAIA or IAi. These occur when there is at least one IA allele and no IB allele present.

List the genotypes for blood type B

Blood type B can also have two genotypes: IBIB or IBi. These occur when there is at least one IB allele and no IA allele present.

List the genotypes for blood type AB

Blood type AB has only one genotype: IAIB. This occurs when both IA and IB alleles are present, and they are both expressed due to their codominant relationship.

List the genotypes for blood type O

Blood type O has a single genotype: ii. This occurs when both alleles are the recessive 'i,' which means neither the A nor B antigens are present on the red blood cells.

Determine the mode of inheritance

The mode of inheritance for the ABO blood types is codominance because both IA and IB alleles can express themselves simultaneously when paired together, resulting in the AB blood type. The A and B blood types show dominance (or partial dominance) over the O blood type due to the presence of the IA or IB allele over the recessive 'i.'

Key concepts

Genotypes of Blood Types

Understanding the genotypes of blood types is fundamental in comprehending how our bodies determine blood type. The ABO blood system is based on the presence or absence of two main antigens, A and B, on the surface of red blood cells. These antigens are governed by three alleles: IA, IB, and i.

For blood type A, the possible genotypes are IAIA (homozygous) or IAi (heterozygous). This means an individual with type A blood could have received the IA allele from both parents, or the IA allele from one parent and the i allele from the other.

In the case of blood type B, we observe a similar pattern with genotypes IBIB and IBi. Individuals inherit the IB allele from one or both parents, leading to the expression of the B antigen.

As for type AB blood, it is unique because its only genotype is IAIB. The presence of both codominant alleles results in the expression of both antigens A and B.

Lastly, blood type O's genotype is ii, consisting of two recessive alleles, which means neither the A nor B antigens are present.

Through understanding these genetic combinations, we can predict blood type inheritance and potential donor-recipient compatibility in blood transfusions.

Codominance in Genetics

Codominance is a form of inheritance where two different alleles at a gene locus are both fully expressed in a heterozygous individual. In the ABO blood group system, this is illustrated by the presence of both A and B antigens on the red blood cells of individuals with type AB blood.

Unlike incomplete dominance, where a blend of traits is observed, codominance shows both traits distinctly. For example, the phenotype of someone with genotype IAIB will express attributes of both type A and type B blood due to the codominant nature of the IA and IB alleles.

This genetic phenomenon showcases that neither allele is recessive in the pair, which can lead to more diverse presentations within offspring when both parents carry different alleles. Understanding codominance is crucial when studying inheritance patterns as it can influence the probability of particular traits within a population.

Inheritance of Blood Types

The inheritance of blood types is a classic example of Mendelian genetics with a twist due to the presence of multiple alleles. Each person inherits one allele from each parent, resulting in a combination that determines their ABO blood type.

When discussing inheritance, we need to remember the dominance hierarchy. The alleles IA and IB are dominant over i, which is why the O type is expressed only when an individual is homozygous recessive (ii). However, IA and IB exhibit codominance with each other, resulting in the AB blood type.

Parents with type A and type B could have children with type A, type B, type AB, or type O blood, depending on their genotype. The allele combination passed down to their offspring is subject to chance, with each parent contributing one allele.

It's important to note that a child's blood type can sometimes help infer, but not definitively determine, parentage. Determining the potential blood types of offspring can be made using a Punnett square, a tool that maps out the likelihood of various allele combinations from the parents.