Exploring Mendelian Genetics Chapter 11, Section 3

The Complexity of Inheritance Mendel studied simple characteristics in pea plants and was able to define some basic principles behind their inheritance patterns However, many characteristics visible in organisms have more complex inheritance patterns than those studied by Mendel

Incomplete Dominance r w rw Pink Neither allele is dominant over the other, therefore the heterozygous phenotype is an intermediate (or BLEND) of the two homozygous phenotypes

Codominance R W RW Roan Both alleles are visible in the heterozygous phenotype Ex: Roan Coat (both red and white hairs) AB blood (both A and B antigens)

Multiple Alleles When there are more than 2 alleles in the population Phenotype Genotype A IAIA, IAi B IBIB, IBi AB IAIB O ii When there are more than 2 alleles in the population Ex: Blood Type (IA, IB, i) Coat color in Rabbits (C, cch, ch, c)

Polygenic Inheritance When two or more genes control the trait The more genes that control the trait, the more variation in phenotypes Ex: Height, eye color, skin color in humans Feather color in parakeets Green Blue Yellow White BBYY BByy bbYY bbyy BbYY Bbyy bbYy BBYy BbYy

The Environmental Influence Environmental factors (such as temperature, sun exposure, altitude, diet, exercise, etc.) can have significant effects on the phenotypes of certain organisms In general, the product of a genotype is not typically a defined phenotype, but rather a range of possibilities influenced by the environment.