A couple and some of their relatives are screened for Gaucher disease in a community-based screening program. The woman is homozygous for the dominant allele, represented by G. The woman's father, sister, and paternal grandmother are heterozygous carriers of the mutant allele, represented by g. Her paternal grandfather, her mother, and both of her mother's parents are homozygous for the dominant allele. The man is heterozygous and he has a brother with Gaucher disease. The man's parents and grandparents have not been tested, but it is known that none of them has Gaucher disease.
Explain why you are able to assign genotypes to the man's parents despite their not being tested.

Question

A couple and some of their relatives are screened for Gaucher disease in a community-based screening program. The woman is homozygous for the dominant allele, represented by G. The woman's father, sister, and paternal grandmother are heterozygous carriers of the mutant allele, represented by g. Her paternal grandfather, her mother, and both of her mother's parents are homozygous for the dominant allele. The man is heterozygous and he has a brother with Gaucher disease. The man's parents and grandparents have not been tested, but it is known that none of them has Gaucher disease.
Explain why you are able to assign genotypes to the man's parents despite their not being tested.

Explain why you are able to assign genotypes to the man's parents despite their not being tested.

Accepted Answer

Hi, everyone. Let's take a look at this practice problem together, three unaffected Children and one with Gauthier disease are born to two healthy parents. If capital M is the for the healthy gene and lower case M for Gauthier disease, what are the parents genotypes? The answer options are a capital M capital, M for parent one, capital M capital M for parent two. So both parents are homozygous dominant option B capital M lowercase M for parent one capital M lowercase M for parent two. So both parents are headers, I guess C lower case M lower case M for parent one and lower case M lower case M for parent two. So both parents are homozygous recessive and option D is capital M lowercase M for parent one and lowercase M lowercase M for parent two. So one parent is heterozygous and the second parent is homozygous recessive. Now, we know from the question that both parents are not affected with Gauthier disease, they have the healthy phenotype and we know that the capital M represents the unaffected gene. That means that both parents had at least one dominant ally since they do not have Gauthier disease. Therefore, the possible parental genotypes are either heterozygous capital M lowercase M or homozygous dominant. So capital M, capital M, knowing this information, we can eliminate option C since both parents are homozygous recessive and the parents must have at least one dominant. A little, we can also eliminate option D since the second parent in the answer is homozygous recessive. And remember both parents need to have at least one dominant A lil. This means the answer is either option A or option B. Now, for option one, all offspring would be homozygous dominant. So all offspring would have capital M capital M genotype as that's the only type of a lil the parents can pass on. Thus, in this example, all offspring would not inherit Gauthier disease. That means we can eliminate option A as well. Since we know one child inherited Gauthier disease, the correct answer is option B where both parents are heterozygous. Now you can confirm this using a punted square and the results of that cross are on the screen. If you analyze the cross, you find that three of the offspring are heterozygous, meaning they do not inherit Gauthier disease. And one offspring inherits Gauthier disease because they inherit two recessive ailes or the affected A lil. So the correct answer is option B capital M lowercase M for parent one and capital M lowercase M for parent two. All right, everyone. I hope you found this helpful and I'll see you soon. For the next practice problem.

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Key Concepts

Autosomal Recessive Inheritance

Genotype Inference from Phenotype and Family History

Dominant vs. Recessive Allele Notation and Interpretation