1. Inheritance Patterns Not all genes migrate and follow strict Medelian patterns. Because of this a spectrum of dominance was created. Complete Dominance – Mendelian pattern of the F 1 (heterozygote) being indistinguishable from the dominant (homozygote) phenotype Codominance – both effect the phenotype in distinguishable ways – blood types are an example (A & B are dominant, O is recessive)

2. Inheritance Patterns Incomplete Dominance – the expression of the dominant phenotype is lessened by the existence of the recessive gene – Red & White true breeding snapdragons form pink F 1 offspring – the degree to which the dominant gene is expressed is called penetrance Tay Sachs is a disease that causes fat accumulation in the neural tissues of children leading to death in the homozygous individual. The disease is due to the loss of function of a needed enzyme. – Although the allele for the disease is dominant the heterozygote does not exhibit disease symptoms. 1/2 of the enzyme production is sufficient to eliminate symptoms. – The disease has very low penetrance on the heterozygous state.

3. Aberrations of Mendelian genetics Frequency of recessive alleles – in many instances the recessive allele is much more common than the dominant allele – polydactally (6 or more digits) is a dominant trait but only expressed in ~1/400 births because the majority of the population is homozygous for the recessive gene Multiple alleles – most than 2 form of alleles exist for most human traits (unlike Mendel's 2 allele peas) – bood type I A, I B, & i (O) Pleiotropy – most genes exert more than one phenotypic effect (pick any genetic disease)

4. Aberrations of Mendelian genetics Epistasis – a gene at 1 locus alters the effect of a gene at another – hair color is effected by a gene at a different locus that is responsible for deposition of the pigment in the follicles – if the animal is homozygous for the color gene the animal is white even though it may be homozygous for the pigment (black) Polygenic Inheritance (quantitative inheritance) – describes traits that are effected by inheritance of genes on different chromosomes – the effect of the traits may be additive or pleiotrophic – skin color is additive with at least 3 genes inherited on 3 different locus and different genes – gives us a distribution of skin color instead of dark brown, tan, or white Nature vs Nurture – the environment in which an organism lives can alter its phenotypic expression

5. Pedigree Chart Recessive disorders – homozygous individuals are called carriers – cystic fibrosis – sickle-cell – mating of close relatives increases the penetrance of recessive disorders Dominant disorders – achondroplasia – Huntington's Multifactoral (Nature + Nurture) – diseases that have a genetic basis but there penetrance is tied to environmental issues – heart disease – diabetes (type II)

6. Testing Fetal testing – amniocentesis - looking at cells from the amniotic fluid in the 14th to 16th week – chorionic villi sampling (CVS) investigation of the cells from the placenta newborn screening – PKU – Tay Sachs – Hemophilia Genetic counseling – offered to individuals related to or who have genetic diseases