Studied by 4 people
Degrees of dominance
Complete dominance- occurs when phenotypes of the heterozygous and dominant homozygote are the same heterozygote and dominant homozygote are the same
incomplete dominance- occurs when phenotype of hybrid offspring is somewhere in between two parental phenotypes
Codominance- occurs when two dominant alleles affect the phenotype in separate, distinguishable ways
Recessively Inherited Disorders
create “carriers” who are heterozygous but phenotypically normal, for example albinism
Multiple alleles (more than 2)
most genes actually exist in more than 2 forms
for example, 4 phenotypes of the ABO blood groups determined by 3 alleles of the gene:
Ia and Ib (codominant) and I (recessive)
Specific carbs added to the surface of blood cells; Ia adds the A carb, Ib adds the B carb; I adds neither, IaIb adds both
Pleiotropy (pleiotropic genes)
genes that have multiple phenotypic effects
Can be responsible for multiple symptoms of certain hereditary diseases (ex. Cystic fibrosis and sickle-cell disease)
Epistasis (epistatic genes)
gene at 1 locus alters phenotypic expression of a gene at a 2nd locus
Ex. Labrador retrievers coat color depends on 2 genes
one gene determines the pigment color (w/ alleles B for black and b for brown) and the other gene (w/ alleles E for color and e for no color m) determines whether the pigment will be deposited in the hair
Polygenic Inheritance
quantitative characters vary along a continuum
Quantitative variation usually indicates polygenic inheritance, an additive effect of 2 or more genes on a single phenotype
Ex. Human skin color
Nature and nurture: environmental impact on phenotype
another departure from Mendelian heretics arises when the phenotype for a character depends on environment as well as genotype
Phenotypic range is generally broadest for polygenic traits, which are called multi factorial because genetic and environmental factors collectively influence phenotype
