Mendelian Genetics

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1. Introduction

Sickle cell anemia is a dangerous genetic condition that results in malformed red blood cells. Instead of a typical flat blood cell, cells of affected people are shaped like sickles, hence the name. In order to predict the risk of inheriting the condition, we need to understand how sickle cell anemia is inherited. For this lab, we’ll construct a family genogram and study blood samples to identify family members affected with sickle cell and determine the rules that govern the inheritance of this condition.

2. Methods

Using squares to represent males and circles to represent females, the family history and blood samples provided were used to create the following pedigree. Family members with sickle cell anemia are designated by shading their shape.

(Figure 1 omitted for preview. Available via download)

3. Data

Based on blood samples, it was determined Louis, and his children Irene, Fred, and Elizabeth all have sickle cell anemia. Irene married Henry, who also suffers from sickle cell and their three children, Victor, Samuel, and Anthony, have inherited the condition. Neither Susan nor her husband Nicholas has sickle cell anemia, but two of their five children, William and April have inherited the condition.

4. Results

By examining the genogram, or pedigree, we can determine that inheritance of sickle cell anemia is based on Mendelian principals of genetics. Mendelian inheritance in humans has been shown to past certain genes for sickle cell anemia, albinism, and other conditions.  We can also deduce that the sickle cell gene is recessive and that Alice must have the sickle cell trait, one sickle cell gene, and one regular gene. Louis presents with sickle cell anemia, so he must have two sickle cell genes.

The first generation of children have all inherited one sickle cell gene from Louis, but only Irene, Fred and Elizabeth have inherited a sickle cell gene from Alice. Since Victoria, Sarah and Susan have a sickle cell gene from Louis and a normal gene from Alice, they have only the trait.

The second generation gives additional evidence that sickle cell is a recessive gene and follows Mendelian principals. Both Harry and Irene have sickle cell anemia. This means that each has two sickle cell genes, and will pass one to each child. Each child has two sickle cell genes and so presents with sickle cell anemia. In the case of Susan and Nicholas though, since only April and William have sickle cell, we know that both Susan and William must have the sickle cell trait. In the case of William and April, both Susan and Nicholas have passed their sickle cell genes. The other three girls though received at least one normal gene.