BIO- exceptions to Mendel

Mendel’s Main Ideas

• One gene per trait

• Two possible alleles; one complete dominate, one recessive

• Could predict phenotype from genotype

• Inheritance of one gene did not affect inheritance of another

Complete Dominance

Dominant gene masks effect of recessive gene (Mendel)

Incomplete Dominance

• intermediate phenotype halfway between two parents

• Red x White= pink

Codominance

• Both genes express slightly different, but not exclusive traits

• Red x White= Red and White marbled flower

Number of Possible Alleles

• Number of possible alleles also affects outcome (not just 2 possibilities)

• more alleles means more possible genotypes

Human ABO Blood Types

• Complex system with 3 possible alleles and codominant relationship

• Gene encodes antigens on red blood cells

• Phenotypes are bllod types

• 6 dif Genotypes

Multiple Genes for a Single Trait

• Multiple loci may determine a single trait

• Alleles are usually additive in their effect

• The more copies of alleles for expressing a trait results in stronger phenotype

• Height and skin color are examples

• Alleles can either be high or low expression

• Genetics determines rage of gene expression; environment determines where in genetic range you fall

Environmental Effects on Phenotype

• Individuals with the same genes can be affected by the environment

• Nutrition is a big factor in humans

• Developmental environment is also important

• Inside the womb is the most important environment in the development of complex traits

Linkage

If two genes are located on the same chromosome they will be inherited as a group unless they change in recombination in meiosis