Question

Both Mr. and Mrs. Brown suffer from an autosomal recessive condition that makes them anemic. Mr. Brown has one amino acid substitution in the \(\beta\) -chain of his hemoglobin molecules and Mrs. Brown has a similar defect in her \(\alpha\) -chain. Neither Betsy nor Boopsy, their children, are anemic. Explain.

Short answer

Betsy and Boopsy are not anemic because they did not inherit a mutated copy of both the HBA and HBB genes from their parents. They either inherited both normal copies or only one of the mutated genes, which doesn't result in the autosomal recessive anemic condition.

Step-by-step solution

Understand Autosomal Recessive Inheritance

Autosomal recessive inheritance is a mode of inheritance in which a trait is only expressed when an individual has two copies of a recessive gene. In this case, Mr. and Mrs. Brown both suffer from an autosomal recessive condition that makes them anemic.

Analyze the Amino Acid Substitution in Hemoglobin Molecules

Hemoglobin is a protein in our red blood cells that carries oxygen from our lungs to the rest of our body. It is made up of four polypeptide chains: two α-chains and two β-chains. Mr. Brown's hemoglobin molecules have a mutation in the β-chain, while Mrs. Brown's hemoglobin molecules have a mutation in the α-chain.

Understand the Mendelian Inheritance for Hemoglobin Molecules

There are two genes involved in the production of hemoglobin: the HBA gene codes for the α chain, while the HBB gene codes for the β chain of hemoglobin. In this case, Mr. Brown will carry the mutated HBB gene and Mrs. Brown will carry the mutated HBA gene. It's important to note that we each have two copies of each gene, one inherited from each parent. Since the condition is autosomal recessive, Mr. and Mrs. Brown will each have one normal copy of the gene and one mutated copy.

Determine the Genetic Inheritance of the Children

In order for a child to be anemic, they would need to inherit a mutated copy of both the HBA and HBB genes. The children may have the following genetic combinations from their parents: 1. Inherit a normal copy of both the HBA and HBB genes. 2. Inherit a mutated copy of the HBA gene and a normal copy of the HBB gene. 3. Inherit a normal copy of the HBA gene and a mutated copy of the HBB gene. 4. Inherit a mutated copy of both the HBA and HBB genes.

Conclusion

Betsy and Boopsy are not anemic because they did not inherit a mutated copy of both the HBA and HBB genes from their parents. They either inherited both normal copies or only one of the mutated genes, which doesn't result in the autosomal recessive anemic condition.

Key concepts

Amino Acid Substitution

When discussing genetic disorders, we often hear about amino acid substitution causing changes in proteins. This occurs when one amino acid in a protein sequence is replaced by another due to a mutation in the DNA. This single change can have a significant impact on the protein's structure and function. For example, the alteration in the hemoglobin molecule, as seen in Mr. Brown's \beta-chain and Mrs. Brown's \(\alpha\)-chain, may disrupt its ability to effectively carry oxygen, contributing to conditions like anemia.

In the case of Mr. and Mrs. Brown, the amino acid substitutions are different, suggesting different mutations occurred in their respective genes. These mutations do not have a cumulative effect because each affects a different chain of the hemoglobin molecule. Indeed, these mutations are specific and, if inherited alone, they are not sufficient to cause anemia in their children, Betsy and Boopsy, as they each lead to a different form of the condition.

Hemoglobin Molecule Structure

The hemoglobin molecule plays a vital role in transporting oxygen in the blood. Hemoglobin is composed of four polypeptide chains – two \(\alpha\)-chains and two \(\beta\)-chains, which come together to form a quartet that can bind oxygen molecules. Each chain is essential for the molecule's oxygen-carrying capacity.

Within this complex, the \(\alpha\)-chains and \(\beta\)-chains must be correctly formed and without mutations for the hemoglobin to function normally. This means that when studying genetic conditions like the one affecting Mr. and Mrs. Brown, we must understand that even if their children inherited one normal \(\alpha\)-chain from Mrs. Brown and one normal \(\beta\)-chain from Mr. Brown, they won't exhibit symptoms of anemia, as both types of chains need to be affected to struggle with the disorder.

Mendelian Inheritance Patterns

Mendelian inheritance patterns describe how certain characteristics are passed from parents to offspring through their genes. In autosomal recessive inheritance, a child must inherit two copies of the recessive gene, one from each parent, to display the associated trait or condition. If they inherit just one recessive gene, they are considered a carrier, but typically will not display symptoms.

For the Brown family exercise, both Betsy and Boopsy don't show symptoms of anemia because they didn't inherit two mutated genes – one mutated \(\alpha\)-chain gene from Mrs. Brown and one mutated \(\beta\)-chain gene from Mr. Brown. Their genetics exhibit the essence of Mendelian inheritance patterns, where an individual only expresses a recessive trait if they inherit two recessive alleles. This understanding of inheritance patterns is crucial in predicting genetic disorders and counseling families on their likelihood.