Exceptions to Mendel’s Rules Mendelian Exceptions Exceptions to Mendel’s Rules

Incomplete Dominance When the heterozygous genotype of a trait shows neither a dominant or recessive phenotype, but rather a mixture. Ex. Carnation flowers – dominant red allele and recessive white allele results in pink phenotype http://www.jerseyproduce.com/images/15-spray-carnations-fern.jpg

Incomplete Dominance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. http://www.parkseed.com/product_images/2563.jpg

Incomplete Dominance

Codominance When the heterozygous genotype expresses both the dominant and recessive phenotypes at the same time Ex. Blood types – this is how you can have an AB blood type Sickle-Cell Anemia

Codominance Codominant Blood Type A Blood Type AB (Codominant) Blood Type O Blood Type B Blood Type A Type B O allele B allele A allele U.S. National Library of Medicine

Multiple Alleles More than two different alleles can exist for a particular trait, but only two can be present at any given time. Ex. Blood Types – This is how you can have A, B, AB, or O type blood. Phenotype Genotypes O ii A IAIA, IAi B IBIB, IBi AB IAIB

A O B AB BO O AO OO Blood Type Cross Parents: AO x BO Offspring Phenotypes: ¼ Type A ¼ Type B ¼ Type AB ¼ Type O B AB BO http://science.uwe.ac.uk/projectshowcase/blood_cells%20copy.JPG O AO OO

Blood Type Cross I A I B I B I A B I B i I A i I B i

Polygenic Inheritance When a phenotypic result is controlled by the added results of the effects of many genes Examples: Height Weight Skin Color Hair Color Eye Color

Polygenic Inheritance P generation X aabbcc AABBCC (very light) (very dark) X F1 generation AaBbCc AaBbCc