Are the following genetic mutation positive for the 3 characteristics listed bel

Question

Are the following genetic mutation positive for the 3 characteristics listed below - Phenylketonuria (PKU), Smith-Lemli-Opitz syndrome (SLOS), Alzheimer’s disease, Sickle cell anemia?

1. It is inherited (at least in some individuals or families) as a single-gene disorder (this means that a disorder where many cases are due to a mix of multiple contributing genes and environmental factors, such as heart disease or Alzheimer’s, could still be chosen if you focus on those instances with a single-gene cause)

2. It demonstrates at least one non-Mendelian characteristic (incomplete penetrance, variable expressivity, sex inflence, sex limited multiple alleles, or incomplete dominance) in its inheritance pattern

3. It is caused by mutations in a gene that has been identified and characterized.

Explanation / Answer

1.

Sickle cell anemia occurs due to a single gene disorder, i.e. Hbs gene. Phenylketonuria (PKU) is also an inherited disorder; it is inherited in autosomal recessive pattern as a result of a single gene i.e. mutation of PAH gene. Smith-Lemli-Opitz syndrome (SLOS) also occurs due to a single gene disorder; the cause of the disease is DHCR7 gene.

Alzheimer’s disease is a neurodegenerative disease. It does not occur due to a defective gene; it occurs when brain cells start dying. Many genes are involved in causing this disease.

2.

Sickle cell anemia is inherited in a Mendelian fashion.

PKU is inherited in Mendelian fashion, but it shows non-Mendelian characteristic; it shows pleiotropic effects. SLOS also shows non-Mendelian characteristic of variable expressivity. Alzheimer’s disease shows incomplete penetrance.

3.

PKU and SLOS occur due to mutation in a gene that has been identified and characterized (names of genes mentioned in part 1).

Note that sickle cell anemia and Alzheimer’s disease do not occur due to mutations in any genes.

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