Chart that shows genetic connections among individuals Pedigrees Chart that shows genetic connections among individuals The knowledge of Mendelian patterns is used to suggest basis of inheritance for a trait Uses standardized symbols so that everyone understands what is being shown

symbol definition female male mating between male & female mating with no children monozygotic twins [identical] dizygotic twins [non-identical]

symbol definition affected individuals carrier for autosomal trait [often not shown] carrier for sex-linked trait [often not shown] offspring of unknown gender x ‘x’ offspring of the same gender individual died prematurely

Types of pedigrees By analyzing a pedigree you can determine the type of inheritance for the trait. Traits are either dominant or recessive. Traits are either on the X chromosome or they are autosomal. examples

1. Autosomal Recessive Inheritance Features both unaffected parents of affected individual must be heterozygous I II III affected individuals may skip generations males & females equally affected father to son transmission possible

1. Autosomal Recessive Inheritance

Galactosemia Caused by autosomal recessive allele Gene specifies a mutant enzyme in the pathway that breaks down lactose enzyme 1 enzyme 2 enzyme 3 GALACTOSE-1- PHOSOPHATE GALACTOSE-1- PHOSOPHATE LACTOSE GALACTOSE + glucose intermediate in glycolysis

2. Autosomal Dominant Inheritance Features half of the children of an affected parent are affected I II III trait does not skip generations males & females equally affected father to son transmission is possible

2. Autosomal Dominant Inheritance

Huntington Disorder Autosomal dominant allele Causes involuntary movements, nervous system deterioration, death Symptoms don’t usually show up until person is past age 30 People often pass allele on before they know they have it

Acondroplasia Autosomal dominant allele In homozygous form usually leads to stillbirth Heterozygotes display a type of dwarfism Have short arms and legs relative to other body parts Father and son, both with achondroplasia

3. X-linked inheritance Features more males are affected II III more males are affected may skip generations father to son transmission is NOT possible only females can be carriers

3. X-linked inheritance

Examples of X-Linked Traits Color blindness Inability to distinguish among some of all colors Hemophilia Blood-clotting disorder 1/7,000 males has allele for hemophilia A Was common in European royal families

Fragile X Syndrome An X-linked recessive disorder Causes mental retardation Mutant allele for gene that specifies a protein required for brain development Allele has repeated segments of DNA Brothers, the younger has Fragile-X syndrome.

Hutchinson-Guilford Progeria Mutation causes accelerated aging No evidence of it running in families Appears to be dominant Seems to arise as spontaneous mutation Usually causes death in early teens

Determining inheritance patterns based on pedigrees

Therefore is autosomal dominant. What type of inheritance? 1. Are both genders affected equally? Yes. Not X-linked 2. Is there any father to son transmission? Yes. Not X-linked No. 3. Does the trait skip generations? Not recessive Therefore is autosomal dominant.

Therefore is Autosomal recessive What type of inheritance? 1. Are both genders affected equally? No. Maybe X-linked 2. Is there any father to son transmission? Yes. Not X-linked. 3. Does the trait skip generations? Yes. Recessive. Therefore is Autosomal recessive

Therefore this is a autosomal, recessive trait. What type of inheritance? 1. Are both genders affected equally? Yes. Not X-linked 2. Is there any father to son transmission? Yes. Not X-linked. 3. Does the trait skip generations? Yes. Recessive. Therefore this is a autosomal, recessive trait.

Now, can we determine the genotypes of the individuals in the pedigree? 1. Start with determining the inheritance type. 2. Once we know this, we assign the genotype to the known individuals: If autosomal dominant trait  the unaffected are aa If X-linked recessive  the affected males are XaY and the affected females are XaXa If is autosomal recessive, the affected individuals are aa

How do we determine the genotypes of the individuals in this pedigree? 1. Determine inheritance We just did  it’s autosomal recessive 2. Assign the affected individuals as ‘aa’ 3. Any unaffected parent of an ‘aa’ individual must be ‘Aa’

Aa aa Aa A_ Aa aa A_