Other Patterns of Inheritance Learning Objectives Describe some

Other Patterns of Inheritance

Learning Objectives § Describe some of the exceptions to Mendel’s principles. § Explain the environment’s role in the way genes determine traits. Vocabulary § incomplete dominance-one allele is not completely dominant so the heterozygous offspring are intermediate. Ex. In some flowers red X white = pink. § codominance-both alleles are expressed, therefore both are capitalized. Ex. Black rooster (BB) X white hen (WW) = speckled chicks (BW). § multiple alleles-more than two forms of an allele. Ex. Humans have three alleles for blood type A, B and o. A (AA or Ao), B (BB or Bo), AB (AB) and O (oo).

Vocabulary § Polygenic traits-most traits are not controlled by a single gene but many, so they show a wide range of phenotypes that can usually be represented by a bell curve. Examples in humans would be: height, intelligence, eye color, skin color, etc.

Incomplete Dominance • Some alleles are neither dominant nor recessive. • Incomplete dominance: One allele is not completely dominant over another.

Codominance • The phenotypes for both alleles are clearly expressed. • Examples: chicken feather color, human protein controlling blood cholesterol levels

Multiple Alleles Many genes exist in more than two forms. Examples: human blood types, fur color in rabbits

Polygenic Traits • Many traits are produced by the interaction of several genes. • Examples: eye color in fruit flies, coat color in dogs • Traits typically show a wide variety of phenotypes.

Genes and the Environmental conditions can affect gene expression and influence genetically determined traits (epigenetics). phenotype The determined by its of an organism is only partly. genotype