and Genetics Part 2:

Classic/Complete Dominance Classic Dominance: (aka “complete dominance”) the heterozygote displays the dominant phenotype. It doesn’t always work this way, though …

Observation: A Litter of Puppies

Dad 2? Dad 2? Dad 1? Dad 1? Mom Mom Dad 2 is the sire of the litter! Which is Dad?

How is that possible?? Many traits have complex inheritance. They can involve more than two alleles! (Example: blood types) May not be as simple as complete dominance Sometimes involves more than 1 gene! (Examples: eye color, height, skin color) In the case of the dogs shown in the previous two slides, there are 2 separate gene locations that control coat color.

Incomplete Dominance Incomplete Dominance: occurs when offspring have a phenotype that is in between the two parent phenotypes. Incomplete Dominance: occurs when offspring have a phenotype that is in between the two parent phenotypes. Heterozyote displays a blended phenotype (dominant no longer masks recessive!) Heterozyote displays a blended phenotype (dominant no longer masks recessive!) Ex) Four o’clock flowers Ex) Four o’clock flowers Get ready to write in the answers to the example and Square 1! Get ready to write in the answers to the example and Square 1!

Incomplete Dominance Example Four o’clock flowers (This is square 3 on your notes sheet) Show a cross between two heterozygous pink flowers. Genotypic ratio: 1 RR : 2 Rr : 1 rr Phenotypic ratio: 1 Red : 2 Pink: 1 white R r RR rrRr Rr There is only 1 genotype per phenotype! GenotypePhenotype RRRed Flowers rrWhite Flowers RrPink Flowers RrX Rr

Now, you try it! Complete squares 2 and 3 on your fill-in notes sheet using the “rules” from our Four ‘O Clock Flowers example. Complete squares 2 and 3 on your fill-in notes sheet using the “rules” from our Four ‘O Clock Flowers example.

Codominance Codominance: both alleles are expressed in a heterozygote. Codominance: both alleles are expressed in a heterozygote. Neither allele is recessive! Neither allele is recessive! Both show up in the phenotype – there is no “in between” like with incomplete dominance. Both show up in the phenotype – there is no “in between” like with incomplete dominance. Examples: Examples: blood types, blood types, spotted cows, spotted cows, spotted flower color spotted flower color

SPECIAL CASE: How to write genotypes for codominant alleles Notation: Notation: USE WITH CODOMINANCE ONLY! USE WITH CODOMINANCE ONLY! Example: Example: Codominance in cow coat colors Codominance in cow coat colors C Represents the gene for coat color R The allele for the color (in this case, it is red) C R C R Genotype written as: Phenotype written as: Red

CRCR CRCWCRCW Genotypic Ratio: GenotypePhenotype C R Red Coat CWCWCWCW White Coat C R C W Roan Coat Codominance Example Roan Coat Color in Cattle Show a cross between a red bull and a roan cow. C R C R X C R C W CRCR CWCW CRCR CRCRCRCR CRCRCRCR CRCWCRCW 2 C R C R : 2 C R C W Phenotypic Ratio: 2 Red Coat : 2 Roan Coat

Blood type = Codominance and Multiple Alleles There are 3 alleles for blood genotypes: I A, I B, i There are 4 blood phenotypes: A, B, O, AB I A and I B are codominant; both are expressed for blood type AB. Type O, which has genotype ii, is recessive to both A and B. The only one that is Codominant! GenotypesPhenotypes I A I A or I A iType A I B I B or I B iType B i Type O I A I B Type AB Multiple alleles!

Blood Type Example Blood Type Example (write this down!) A woman has Type A blood and her genotype is I A i She marries a man who is Type B with genotype I B i. What are the possible blood types of their children? IAIA i i IAIBIAIB IAiIAi IBiIBi ii Type ABType A Type BType O The possible offspring blood types are: Type AB, Type A, Type B, and Type O IBIB

Back to the dog example from yesterday… Dam (mom): KkYY Sire (dad): kkyy There are TWO alleles for Coat Color K = Black k = Not Black Y = Red y = Tri-color The Pups are: KkYy = Black kkYy = Red

To Sum Up Classic Dominance: Incomplete Dominance: Codominance: Dominant Phenotype X An “in between” of the dominant and recessive X Both alleles are displayed