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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- F1 generation Incomplete Dominance- F2 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. Codominance Black Checkered White White chicken Black chicken W W B B BW BW Checkered BW Checkered Checkered BW Checkered Roan Horse http://search.vadlo.com/b/q?rel=2&keys=Dominance+Incomplete+Dominance+Codominance+PPT Roan Cattle http://www.ccs.k12.in.us/chsteachers/BYost/Biology%20Notes/CH11notescoincompletedom_files/image004.jpg Variegated Clover http://3.bp.blogspot.com/_zUPrgMM5tUg/SSVdrs59_uI/AAAAAAAAAA8/qJGjG2nZPhk/s200/codominance.GIF 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. Chapter 11 Complex Inheritance and Human Heredity 11.2 Complex Patterns of Inheritance Coat Color of Rabbits Chinchilla Albino Light gray Dark gray Himalayan ABO Blood Type • ABO blood type in humans is determined by three alleles: IA IB i • IA and IB are codominant alleles. • Both IA and IB are dominant to the allele i. Blood Genotype Type IAIA IAi A A IBIB B IBi B IAIB ii AB O Chapter 11 Complex Inheritance and Human Heredity 11.2 Complex Patterns of Inheritance Multiple Alleles Blood groups in humans ABO blood groups have three forms of alleles. Donor-recipient compatibility Recipient Type A B AB O A Donor B AB O = Unsafe transfusion = Safe transfusion © 2007 Paul Billiet ODWS 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.