Question

o Search the internet to find examples of genes with pleiotropy, co-dominance and incomplete dominance in humans that aren’t given in the textbook for Bio 200/201. For each example, write a short paragraph that includes:

▪ What type of inheritance pattern the gene shows

▪ The possible PHENOTYPES and the genotypes that underlie them

▪ What effect the gene has on the overall function and health of the human body.

Answer 1

1. Pleotropy: Marfan syndrome is caused by a mutation in one gene, but affects growth and development, including height, vision, and heart function. This is an example of pleiotropy where one gene affects multiple characteristics. Mutations in the gene for fibrillin-1 (FBN1) cause Marfan syndrome, an autosomal dominant disorder of connective tissue one copy of the altered gene in each cell is sufficient to cause the disease. So disease phenotype will be seen for genotypes AA and Aa, while aa will have normal phenotype.

2. Codominant: A major codominant trait in humans is sickle cell anemia. The altered form of hemoglobin that causes sickle-cell anemia is inherited as a codominant trait. Specifically, heterozygous (Ss) individuals express both normal and sickle hemoglobin, so they have a mixture of normal and sickle red blood cells. It is a disease where red blood cells become thin and elongated. If a person has one copy of the sickle cell allele, half of their red blood cells will be misshapen and cannot transport oxygen. In this way, the allele is codominant, since both normal and sickled shapes are seen in the blood. So Ss genotype will show codominant nature having both phenotypes of sickled RBC and normal RBC. Sickle cell anemia is inherited in an autosomal recessive pattern, which means that both copies of the gene in each cell have mutations to show the diseased phenotype.

3. Incomplete dominance: This is seen in case of Tay Sachs disease. The heterozygote individual produces only half the amount of normal protein as is produced by an individual who is homozygous for the normal allele.This neurological disease is caused by an enzyme imbalance and is also inherited in autosomal recessive pattern where only gentoype with aa will show the disease phenotype.

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