A genetic counselor is evaluating a family\'s risk for an autosomal genetic dise

Question

A genetic counselor is evaluating a family's risk for an autosomal genetic disease and is reviewing the family pedigree and results from a diagnostic screen done using gel electrophoresis. Legend Luis Erica Affected male Unaffected male Affected female Unaffected female Lorena Oscar Diego 1. What is the genotype for each of the family members? Explain your reasoning. 2. Is the disease allele dominant or recessive? What is the evidence for your conclusion? 3. Diego and his phenotypically-normal wife are considering having children. Is there any risk of their children developing this disease? Why or why not?

Explanation / Answer

Genotype of Louis- Homozygous recessive (lets say aa) It shows a the band parallel to the affected gene band in homozygous affected.

Genotype of erica - Heterozygous (Aa) It shows bands parallel to the affected gene as well as another two band which is present in the unaffected homozygous. So it contains one affected as well as non-affected genes but not showing the phenotype so the affected gene must be recessive and she must be heterozygous.

Genotype of Lorena - Homozygous recessive (aa) Because she is affected by autosomal recessive disorder and shows the phenotype so she needs to be homozygous recessive.

Genotype of Oscar- Heterozygous (Aa) His one parent only have recessive allele and one parent have both dominant and recessive allele. so he either will be Aa(not affected) or aa(afftected). As he is not affected he is heterozygous

Genotype of Diego-Heterozygous (Aa) His one parent only have recessive allele and one parent have both dominant and recessive allele. so he either will be Aa(not affected) or aa(afftected). As he is not affected he is heterozygous

2. The disease allele is recessive. This is because the gel result of affected individual shows only one band while the gel result of unaffected individual shows either two or 3 bands (excluding the 1st band which is present in all of them. So the unaffected individual must have either both dominant allele or heterozygous dominant and recessive allele. But the affected indiividual only have one band so it needs to be only homozygous and only recessive allele express itself in homozygous condition.

3. Yes the children of diego and his phenotypically normal wife may be at the risk of disease if his wife is heterozygous normal( Aa)

Aa X Aa

AA

not affected

Aa

not affected

Aa

not affected

aa

affected

25% chance that the children will be affected.

But if his wife is homozygous normal then

Aa X AA

AA

not affected

AA

not affected

Aa

not affected

Aa

not affected

0% chance that any children will be affected.

A a A

AA

not affected

Aa

not affected

a

Aa

not affected

aa

affected

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