1 Human Genetics: Pedigrees

Pedigree Looks at family history and how a trait is inherited over several generations and can help predict inheritance patterns Symbols represent females, males, those who carry or are affected by the trait being examined, and family relationships

Pedigree Symbols Male Heterozygous Male Affected Male Female Affected Female Heterozygous Female Marriage/Mating 1 st Generation of Children New marriage into family

Inheritance Patterns Autosome: any chromosome that does NOT determine sex—humans have 22 pairs of autosomes and one pair of sex determining chromosomes Autosomal Dominant Only one defective copy of the gene is needed for that trait to be expressed. The defective copy is usually the dominant allele. Autosomal Recessive The trait is recessive and can only be expressed when the genotype is homozygous form. The defective copy is usually the recessive allele.

Defective allele is the dominant form of that gene “Normal” form is homozygous recessive Unless it is specifically stated, you can assume that the affected person is a heterozygote In the event that the person is homozygous dominant, the condition is so severe that the person cannot survive Examples: Huntington’s, Marfan Syndrome, Achondroplasia Autosomal Dominant Inheritance

Autosomal Recessive Inheritance The defective allele is the recessive form of that gene BOTH the homozygous dominant and heterozygous phenotypes are “normal” Inbreeding increases the occurrence of the trait