Question

a pedigree is just like a family tree except that it focuses on a specific genetic trait. a pedigree usually only shows the phenotype of each family member. with a little thought, and the hints below, you may be able to determine the genotype of each family member as well!

hints for analyzing pedigrees:

1. if the individual is homozygous recessive, then both parents must have at least one recessive allele (parents are heterozygous or homozygous recessive).
2. if an individual shows the dominant trait, then at least one of the parents must have the dominant phenotype. this one will be pretty obvious when you look at the pedigree.
3. if both parents are homozygous recessive, then all offspring will be homozygous recessive.

note: in a pedigree, the trait of interest can be dominant or recessive. the majority of harmful genetic conditions are only seen when an individual is homozygous recessive - examples of conditions caused by recessive alleles include cystic fibrosis (a disease of the secretory glands, including those that make mucus and sweat), falconi anemia (a blood disorder), albinism (a lack of pigmentation), and phenylketonuria (a metabolic disorder). some genetic conditions are caused by dominant alleles (and may therefore be expressed in homozygous dominant or heterozygous individuals) - examples of conditions caused by dominant alleles include polydactyly (presence of extra fingers), achondroplasia (a type of dwarfism), neurofibromatosis (a nervous disorder), and a disease known as familial hypercholesterolemia in which affected individuals suffer from heart disease due to abnormally high cholesterol levels

human pedigrees
for questions 1 - 9, use the pedigree chart shown below. some of the labels may be used more than once.

1. a male
2. a female
3. a marriage
4. a person who expresses the trait
5. a person who does not express the trait
6. a connection between parents and offspring
7. how many generations are shown on this chart?

assuming the chart above is tracing the dominant trait of \white forelock (f)\ through the family. f is a tuft of white hair on the forehead.

1. what is the most likely genotype of individual \a\? (ff, ff or ff?)
2. what is the most likely genotype of individual \c\? (ff, ff or ff?)

Explanation:

1. In pedigree charts, squares represent males, so a male is represented by a square.
2. Circles represent females in pedigree charts.
3. A horizontal line between a square and a circle represents a marriage.
4. Shaded - in symbols represent individuals who express the trait.
5. Un - shaded symbols represent individuals who do not express the trait.
6. A vertical line from parents to offspring represents the connection between them.
7. By counting the rows of symbols from top to bottom, we can see there are 3 generations.
8. Since individual "A" expresses the dominant trait of white forelock, and some of her offspring have the recessive phenotype (no white forelock), she must be heterozygous (Ff). If she was FF, all her offspring would have the dominant phenotype.
9. Individual "C" does not express the dominant trait, so his genotype must be ff.

Answer:

1. Square
2. Circle
3. Horizontal line
4. Shaded - in symbol
5. Un - shaded symbol
6. Vertical line
7. 3
8. Ff
9. ff