Studying Human Genetics

Gregor Mendel studied peas by crossing different varieties to see what kind of offspring resulted.

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Why can’t we study human genetics in the same way?

1. Tracing traits through families

Geneticists look at traits in a family, like the incidence of sickle cell anemia.

When they see that two individuals without the disorder can have a child with the disorder, they suspect that the gene must be recessive.

2. Pedigree Chart

A diagram that shows how a trait is passed through generations.

Squares = males

Circles = females

Shading indicates the presence of the trait studied (Sickle Cell Disease)

Based on the pedigree, you can determine the GENOTYPES of members of the family.

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3. Practice this chart

4. Some genes are dominant - like polydactyly

5. Why is it illegal to marry your cousin (in most states)?

This pedigree shows the incidence of cystic fibrosis in a family.

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Are children of first cousins in this family more likely to have the disease?

6. Human Genetic Disorders

Albinism - absence of pigment in the skin and eyes

Cystic fibrosis - inability to clear mucus from lungs, can be treated

Sickle cell anemia - abnormally shaped blood cells, can be treated

Tay-Sachs - cells lack the ability to remove waste; brain damage and death

7. Hemophilia - a SEX-LINKED Disorder

The gene is carried on the X chromosome and causes problems with blood clotting.

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Even a small injury could cause a child to bleed to death.

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Females are carriers and can pass the gene to their sons.

Practice Pedigrees on your own!

8. Duchenne Muscular Dystrophy

Do you think DMD is dominant or recessive?

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It it sex-linked?

Causes weakening of the muscles