Pedigree Analysis What’s in YOUR family tree? Pedigree Analysis

 In humans, pedigree analysis is an important tool for studying inherited diseases  Pedigree analysis uses family trees and information about affected individuals to: figure out the genetic basis of a disease or trait from its inheritance pattern predict the risk of disease in future offspring in a family (genetic counseling)

Today….  How to read pedigrees  Determining basic patterns of inheritance 1.autosomal recessive 2.autosomal dominant 3.X-linked recessive 4.X-linked dominant (very rare)  Applying pedigree analysis – practice  Looking at the Blue People of Troublesome Creek

Pedigree Symbols

1.Autosomal recessive pedigree - cystic fibrosis female male affected individuals

1. Autosomal recessive traits Trait is rare in pedigree Trait often skips generations (hidden in heterozygous carriers) Trait affects males and females equally

Autosomal recessive diseases in humans:  Most common ones Cystic fibrosis Sickle cell anemia Phenylketonuria (PKU)  These may be more common because their heterozygotes all give a survival advantage!!  Cystic fibrosis heterozygotes are less likely to die from cholera  Sickle cell heterozygotes are less likely to die from malaria  PKU heterozygotes (females) are less likely to have miscarriages

Sickle Cell / Malaria Connection

2. Autosomal dominant pedigrees Trait is common in the pedigree Trait doesn’t skip generations Affected individuals transmit the trait to ~1/2 of their children (regardless of sex)

Autosomal dominant traits  There are few autosomal dominant human diseases, but some rare traits have this inheritance pattern ex. achondroplasia (a sketelal disorder causing dwarfism)

3. X-linked recessive pedigree Trait is rare in pedigree Trait skips generations Affected fathers DO NOT pass to their sons, Males are more often affected than females

Ex. Hemophilia in European royalty

X-linked recessive traits Red-green color blindness Hemophilia X-linked ichthyosis

4. X-linked dominant pedigrees Trait is common in pedigree Affected fathers pass to ALL of their daughters, but not their sons Doesn’t skip generations

X-linked dominant diseases X-linked dominant diseases are extremely unusual Often, they are lethal (before birth) in males and only seen in females ex. incontinentia pigmenti (skin lesions) ex. X-linked rickets (bones soften/deform)

Pedigree Analysis in real life Keep in mind that pedigrees don’t always give the pattern of inheritance – many factors (like the environment or multiple genes) might be involved!!

CHALLENGE #1 What is the pattern of inheritance? _______________ What are IV-2’s odds of being a carrier? __________

CHALLENGE #2 What is the inheritance pattern? _________________ How do you know? ____________________________ __________________________________________

CHALLENGE #3 What is the inheritance pattern? __________________ Identify the carriers: ___________________________ How many children did I-1 and I-2 have? _____________

Now for CHALLENGE #4!! What is the inheritance pattern? What could have contributed to the frequency of the allele showing up?

CHALLENGE #4