Pedigrees

NGSSS SC.912.L.16.2 Discuss observed inheritance patterns caused by various modes of inheritance, including dominant, recessive, codominant, sex-linked, polygenic and multiple alleles

The four types of inheritance patterns: Genetic conditions caused by a mutation in a single gene follow predictable patterns of inheritance within families The four types of inheritance patterns: Autosomal recessive Autosomal dominant X-linked recessive X-linked dominant

PEDIGREE A pedigree is a tool for studying inheritance in humans (in particular, inherited diseases). It shows the occurrence and appearance (phenotype) of a particular genetic trait, as it is passed from one generation to the next in a family.

How to Read Pedigrees = male = female = parents or = individual who shows the trait = heterozygous carrier of autosomal trait or Figure: FIGURE 12.14 Title: A family pedigree Caption: This pedigree is for a recessive trait, such as albinism. Both of the original parents are carriers. Because the allele for albinism is rare, pairing between carriers is an unlikely event. However, the chance that each of two related people will carry a rare recessive allele (inherited from a common ancestor) is much higher than normal. As a result, pairings between cousins or even closer relations are the cause of a disproportionate number of recessive diseases. In this family, pairings between cousins occurred three times—between III 3 and III 5, III 4 and IV 3, and IV 1 and IV 2. = offspring 1 2 3 = generation I, II, III, IV, or V

More Symbols Identical Twins Non-Identical Twins Deceased Individuals

PATTERNS OF INHERITANCE Autosomal Recessive Trait Seen when individual has 2 copies of allele (One copy of allele, individual is carrier but does not develop condition) Males and females affected equally

PATTERNS OF INHERITANCE Autosomal Dominant Trait Condition expressed in individuals with just one copy of allele Males and females have equal chance of passing on trait to offspring

PATTERNS OF INHERITANCE Sex-linked Recessive Not expressed when one normal allele present Fully evident in males because they have only one copy of X chromosome Women rarely affected unless both X chromosomes carry the allele No father to son transmission, but all daughters will inherit one copy of allele (carrier)

PATTERNS OF INHERITANCE Sex-linked Dominant Located on X chromosome so no father to son transmission but all daughters affected Expressed when only one copy of allele present Carriers are not possible

Your task… Determine the pattern of inheritance for… Cystic Fibrosis Achondroplasia Tay-Sachs Disease Huntington’s Disease

Pattern of Inheritance? Cystic Fibrosis Pattern of Inheritance? autosomal, recessive

Achondroplasia Pattern of Inheritance? autosomal, dominant

Tay-Sachs Disease Pattern of Inheritance? autosomal, recessive

Huntington’s Disease Pattern of Inheritance? autosomal, dominant

Hemophilia Mode of Inheritance? sex-linked recessive