Chemical Biology 03
Dec 9, 2009
Inheritance III-cont.
Continue with analysis of two-gene studies:
Probabilities
Punnett Square
Branch Daigram
Introduction to Pedigree Analysis! tracing the inheritance patterns of human disorders
~10,000 known single-gene human traits
see OMIM (Online Mendelian Inheritance in Man)
most are rare* genetic diseases
allele causing disorder can be recessive OR dominant
Albinism
Cystic fibrosis
Sickle cell anemia
Tay Sachs disease
Thalassemia
* rare = incidence of disease is <1%
Huntington’s Disease
Achondroplasia
Marfan Syndrome
Brachydactyly
Polydactyly Inheritance of albinism
Recessive traits
•unaffected parents of affected children are carriers
•unaffected parents may have affected children
•all the children of two affected individuals are affected
•often appears to “skip a generation” Inheritance of albinism
Aa
aa
or
Aa
aa
?
Aa or AA
•Who can be identified as a carrier?
•What is the genotype of the monozygotic twins?
•If the two-carrier couple have another child - what is
the chance of that child being albino?
•For rare diseases, we can assume that an unrelated
individual is not a carrier.
ex. the mom of the 3 carrier siblings is assumed to
be homozygous dominant since Albinism is not common
Aa x Aa
1 : 2 : 1
AA: Aa: aa or
rare recessive disorders often
show up in consanguinous matings Dominant traits
•appears in every generation (cannot skip!)
•at least one parent of an affected child is affected
•two affected parents may have unaffected children
•an affected parent will transmit the trait to 1/2 progeny
•no “carriers”
•can they be lethal? some pedigrees can be inconclusive