1. Genetic Analysis of Human Diseases Chapter 22.1

2. Overview Due to thousands of human diseases having an underlying genetic basis, human genetic analysis is of great medical importance. The mutant genes that cause these diseases often follow simple Mendelian inheritance patterns.

3. A Genetic Basis for a Human Disease May Be Suggested From a Variety of Observations For human diseases, geneticists would like to know the relative contributions for genetics and the environment. We cannot conduct human crosses to elucidate the genetic basis of a disorder. Must rely on analyzing the occurrence of a disease in families that already exist.

4. How to Determine Genetic Basis When an individual exhibits a disease, this disorder is more likely to occur in genetic relatives than in the general population. – Example: cystic fibrosis Relatives are more likely to have this disease than randomly chosen members of the general population.

5. How to Determine Genetic Basis Identical twins share the disease more often than non-identical twins. – Identical twins = MZ – Fraternal twins = DZ – Concordance – the degree to which a trait is inherited.

6. How to Determine Genetic Basis The disease does not spread to individuals sharing similar environmental situations. – Inherited disorders cannot spread from person to person. – The only way genetic diseases can be spread is from parent to offspring during sexual reproduction.

7. How to Determine Genetic Basis Different populations tend to have different frequencies of the disease. – Due to evolutionary forces, the frequencies of traits usually vary among different populations of people. Example : sickle-cell anemia is highest among certain African and Asian populations.

8. How to Determine Genetic Basis The disease tends to develop at a characteristic age. = age of onset – some diseases develop at birth and some develop much later in life.

9. How to Determine Genetic Basis The human disorder may resemble a disorder that is already known to have a genetic basis in an animal. – In animals, where we can conduct experiments, various traits are known to be governed by genes. Example: albinism. The phenotype of albinism is found in humans as well as many animals. (fig. 22.1 pg. 601)

10. How to Determine Genetic Basis A correlation is observed between a disease and a mutant human gene or a chromosomal alteration. – Identification of altered genes or chromosomes only in individuals exhibiting the disease.

11. 4 Common Features of Autosomal Recessive Inheritance 1.Frequently, an affected offspring will have two unaffected parents. 2.When two unaffected heterozygotes have children, the percentage of affected children is (on average) 25% 3.Two affected individuals will have 100% affected children. 4.The traits occurs with the same frequency in both sexes.

12. Assignment Pg. 630, E1 and E2 – Write out the question and then supply your answer.