Incomplete Dominance, Codominance and Multiple Alleles

INCOMPLETE DOMINANCE Incomplete Dominance- Pattern of gene expression in which the phenotype of a heterozygous individual is intermediate between those of the parents. Cases in which one allele is not completely dominant over another. Example: Snapdragons and Carnations

Incomplete Dominance- F 1 generation

Incomplete Dominance- F 2 generation

CODOMINANCE Codominance- The condition in which both alleles in a heterozygous organism are expressed. BOTH alleles contribute to the phenotype. The two alleles don’t blend, but are rather both present in the offspring. Examples- Checkered Chickens, Roan Horses, Roan Cows, Variegated Clover.

BB W W BW Codominance White chicken Black chicken Checkered BlackWhite

Roan Horse

Roan Cattle Variegated Clover

Multiple Alleles Multiple Alleles- Genes which have more than two alleles. It is common for more than 2 alleles to control a trait in a population Multiple alleles can only be studied in populations since each individual only has 2 alleles for a trait. Examples: human blood types, fruit fly eye color, coat color in rabbits: C, cch, ch, and c.

Complex Inheritance and Human Heredity Coat Color of Rabbits Light gray Dark gray Himalayan Albino Chinchilla 11.2 Complex Patterns of Inheritance Chapter 11

Genotype Blood Type IAIAIAIA A IAiIAiA IBIBIBIB B IBiIBiB IAIBIAIB AB iiO ABO Blood Type ABO blood type in humans is determined by three alleles: I A I B i I A and I B are codominant alleles. Both I A and I B are dominant to the allele i.

Complex Inheritance and Human Heredity Multiple Alleles  Blood groups in humans  ABO blood groups have three forms of alleles Complex Patterns of Inheritance Chapter 11

Donor-recipient compatibility Recipient TypeABABO A DonorB AB O = Unsafe transfusion = Safe transfusion Note: Type O blood may be transfused into all the other types = the universal donor. Type AB blood can receive blood from all the other blood types = the universal recipient. © 2007 Paul Billiet ODWSODWS