1. Another Type of Incomplete Dominance - Codominance

2. Another type of incomplete dominance is referred to as codominance. In this type of interaction, both alleles are expressed at the same time. Shorthorn cattle provide an excellent example of codominance. A red bull crossed with a white cow produces a roan calf. The roan calf has intermingled white and red hair.

3. PARENT #1 (possible gametes) PARENT #2 (possible gametes) Hr Hr Hr Hr Hw Hw Hw Hw Use H to represent the hair colour gene, r to represent the red allele and w to represent the white allele. red bull genotype: white cow genotype: H r H r H w H w F 1 genotypes: all heterozygous F 1 phenotypes: all roan

4. Describe the phenotypic and genotypic ratios of the offspring when two F 1 offspring (both heterozygous) are mated. roan bull genotype: roan cow genotype: H r H w H r H w F 2 genotypes: ¼ homozygous H r ½ heterozygous ¼ homozygous H w F 2 phenotypes: ¼ red ½ roan ¼ white PARENT #1 (possible gametes) PARENT #2 (possible gametes) Hr Hr Hw Hw Hw Hw Hr Hr

5. ABO Blood Types

6. There are 3 different alleles for the ABO gene, resulting in four different ABO blood types. A allele: I A B allele: I B O allele: i The alleles for blood types A and B are codominant but are dominant over the allele for type O. Each allele codes for a different enzyme that places different types of sugars (antigens) on the surface of a red blood cell. The O allele codes for an enzyme that makes a simpler surface molecule that lacks the extra sugars of the A, B, or AB blood types. Type O blood contains no A/B antigens.

8. The body creates the opposite antibodies to the antigen(s) on the RBCs. For example, a person with type A blood has B antibodies in their blood. A person with type O blood has no ABO antigens on their RBCs and produces both A and B antibodies. For example, an individual with type A blood produces an immune response against type B and type AB blood. Since different blood types exist, it is important that individuals who receive blood transfusions receive blood that is compatible with their own.

10. If an incompatible blood type is transfused, the patient’s life may be put at risk because the antibodies produced in the patient’s body react with the antigens on the red blood cells. This interaction causes two events to occur… 1.clumping (agglutination) of the red blood cells 2.production of more of the same antibodies by the patient’s immune system The rhesus factor is a blood factor that is regulated by another gene on different chromosome. The Rh positive allele (R) is dominant and the Rh negative allele (r) is recessive.

11. Sample Problem 1 What is the phenotypic ratio of the offspring from the mating of a heterozygous type B and heterozygous type A individual? P generation genotypes: heterozygous A parent- heterozygous B parent- F1 generation phenotypes: PARENT #1 PARENT #2 ¼ type AB ¼ type B ¼ type A ¼ type O

12. Sample Problem 2 : Indicate the blood types possible from the mating of a male with blood type O to a woman with blood type AB. P generation genotypes: Blood type O man - Blood type AB woman - F1 generation phenotypes:

13. c)Could this woman ever have a child with type O blood? type AB female genotype: type O offspring genotype: Therefore, the type AB female can never have a type O offspring, since she will not have an O allele (i) in any of her gametes.