Human Pedigrees

12.3 pg 255

Pedigrees

Family tree that records and traces the occurance of a trait in a family.

Analyze patterns Applies Mendel’s concepts of

dominant and recessive alleles. Shapes:

Males- squares Females- circles

Pedigree traits

Individuals showing (expressing) the trait are shaded( colored in)

Recessive traits have “ee” genotypes Pedigrees can be analyzed for recessive,

dominant, and sex-linked disorders

Recessive Traits

Most human genetic disorders are in this group.

Range of severity. Examples-

Albinism- lack of pigment TaySachs- fatal nerve disease Cystic fibrosis- defective protein- thick mucous

buildup affects breathing, digestion, liver. 1/25 people of European ancestry are affected in the U.S.

Carrier

Has one allele but does not show the symptoms.

Heterozygous for the trait. Some pedigrees show such

individuals as a half shaded circle. If two carriers have a child there is a

¼ chance the child will have the disorder.

Dominant Traits Only one allele needed to have disorder

(heterozygous Aa or homozygous AA). Less common Disorder is in every generation

Examples- Polydactyl- extra fingers and toes Achondroplasia- dwarfism

All individuals are heterozygous. Homozygous is fatal.

Dominant Traits continued

Note- Dominant alleles are not found more often in populations.

Most dominant disorders are fatal before reproductive age.

Exception-Huntington’s disease- nervous disorder- no symptoms until 30s or 40s- so trait passed on to children.

Sex-linked pedigrees

More men have the trait. Review sex-linked notes

Genetic Counselor

Collects and analyzes family inheritance patterns

Helps interpret genetic test results. PKU- phenyketonuria- tells if baby is

missing and enzyme to process phenylalanine. Diet is critical.

Sweat chloride test- cystic fibrosis. More than 250 different genetic tests

available. Confidentiality and bioethics an issue