Human Pedigree Genetics

HUMAN PEDIGREE GENETICS

Progress in human genetics has proceeded more slowly than general genetics. A geneticist uses experimental results to verify the genotypes and phenotypes of living organisms. The time involved for a new generation of humans to show a certain trait can be several decades. For example, diabetes mellitus in some people may not show up for 30 or 40 years. However, fruit flies are easy to study because new generations develop in only ten to twelve days.

Genotypic and/or phenotypic data of human genetic patterns are usually presented as a diagrammed chart called a pedigree. Some pedigree symbols are shown in Table 23-1. A pedigree shows several generations of a family and the people who married into the family (Figure 23-1). Each person in a pedigree can be identified by the roman numeral for the generation and by his number. One difficulty with a pedigree chart is that sometimes the information is obtained from only a few members of the family. Therefore, it could be inaccurate or unreliable.

Today, geneticists are able to provide a service called “genetic counseling.” Families affected with unfavorable traits can be given advice about the chances of their future children possessing these traits.

In this investigation you are to analyze three family pedigrees. From these pedigrees, you are to determine whether the gene for the trait listed is dominant or recessive and determine the genotype and phenotype of each individual in the family.

PROCEDURE

Study each of the following pedigrees of families with certain hereditary traits. Determine whether each of the traits is dominant or recessive. Determine the genotype and phenotype of each individual in each pedigree. Record the genotypes and phenotypes in your lab notebook.

Pedigree A. Deaf Mutism

Pedigree A. Deaf Mutism

One form of deafness in humans is a type in which the individual inherits not only deafness but also the inability to talk. Use symbols D for dominant, d for recessive.

Pedigree B. Hemophilia

Figure 23-3.

Pedigree B. Hemophilia

Hemophilia is a disease of the circulatory system. It is sometimes called bleeder’s disease because persons with the disease have a very slow clotting time when injured. An affected person could bleed to death from minor wounds or internal injuries. Use symbols H for dominant, h for recessive.

Pedigree C. Brachydactyly

Figure 23-4.

Pedigree C. Brachydactyly

Brachydactyly is a condition in which fingers are abnormally short. The last two joints of the middle finger are shortened. In the other four fingers, the last two joints are fused into one and are also shortened. Use symbols B for dominant, b for recessive.

FORMULATING GENERALIZATIONS

1. Is there any person in any pedigree for whom you cannot determine a genotype or phenotype? List the person by number, for example, Pedigree B, II-1. Give a reason for each person.
2. In hemophilia, how do you account for affected females being stillborn?

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HumanPedGenetics.BWG 06/14/19