EQ: What are incomplete and codominance? Warmup:

Complete Dominance If we cross a tall pea plant and a short pea plant what do we get? Tall. The tall hides the short. Dominant completely hides recessive Which one is dominant and which one is recessive?

Complete Dominance dominant gene totally masks the recessive Mendel investigated complete dominance dominant gene totally masks the recessive

Review Problem: Dominant/Recessive In pea plants, purple flowers (P) are dominant over white flowers (p) show the cross between two heterozygous plants. P p GENOTYPES: - PP (1); Pp (2); pp (1) - ratio 1:2:1 P p PP Pp PHENOTYPES: Pp pp - purple (3); white (1) - ratio 3:1

Exceptions to Mendelian Inheritance

Incomplete dominance What happened when we crossed a red and white flower? Why? Whats dominant and what’s recessive? Is the dominant totally

Incomplete Dominance A cross between two different phenotypes can produce offspring a blending of the parental traits. 

Incomplete Dominance It's like mixing paints Red + white will make pink Red doesn't totally dominate the white, instead there is incomplete dominance, and we end up with something in-between.

Incomplete Dominance

Incomplete Dominance How to recognize a question involving incomplete dominance: the offspring show a 3rd phenotype.  the offspring are different from the parents. the trait in the offspring is a blend of the parental traits.

Incomplete Dominance Can still use the Punnett square to solve problems involving incomplete dominance.  The letters used to represent each allele will be different, lowercase letters Why lowercase? Because neither allele dominates the other

2 homozygous parents still produce 100% heterozygotes! Incomplete Dominance r r r = red flowers w = white flowers rw = pink flowers Cross red and white flowered plants Results? Genotype: 100% rw Phenotype: 100% pink rw rw w rw rw w 2 homozygous parents still produce 100% heterozygotes!

Same as when two heterozygotes mated before Incomplete Dominance A cross between a blue bird & a white bird produces offspring that are silver.  What are the genotypes of the parent birds in the cross? b= blue w= white What is/are the genotype(s) of the silver offspring? bw What would be the phenotypic percent of offspring produced by two silver birds? 25% blue 25% white 50% silver bb x ww b w bb bw ww b w 1 : 2 : 1 ratio Same as when two heterozygotes mated before

ry x ry Incomplete Dominance When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit.  What are the genotypes of the parent orange-fruited plants? 1 : 2 : 1 ry x ry

Codominance What happened when we crossed lentils with big spots with lentils that had small dots. Both showed up…Why? Did the big spots dominate the small spots? Which one is dominant?

red x white = red & white spotted Co-dominance Prefix "co-" means "together“ Cooperate = work together Coexist = exist together The heterozygous organism has a third phenotype in which both of the parental traits appear together. (Not blended). red x white = red & white spotted

Co-dominance A very very very very very common phenotype used in questions about co-dominance is roan fur in cattle.  Cattle can be red, white or roan (red & white hairs together). 

Co-dominance Can still use the Punnett square to solve problems involving co-dominance.  The letters used to represent each allele will be different, CAPITAL letters RR = all red hairs WW = all white hairs RW = red & white hairs together.

Co-dominance How to recognize a question involving co-dominance: Notice that the offspring show a 3rd phenotype.  The parents each have one, and the offspring are different from the parents. Notice that in the offspring BOTH of the parental traits are expressed, not a mix.

Codominance R=roan (reddish Brown) W= White Cross a homozygous white cow with a homozygous roan. What is the phenotypic ratio?

Co-dominance Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull. 50% WW - White 50% WR - Roan What should the genotypes & phenotypes for parent cattle be if a farmer wanted only cattle with red fur? Both parents should be RR, red W W W R WW WR

Co-dominance A cross between a black (BB) cat & a tan (TT) cat produces a tabby (BT) pattern (black & tan fur together). What pattern of inheritance does this illustrate? Co-dominance What percent of kittens would have tan fur if a tabby cat is crossed with a black cat? 0% tan 50 % Tabby 50% Black B B B T BB BT

Codominance Sickle Cell Anemia is also co-dominant. Having sickle cell disease makes your red-blood cells sickle-shaped instead of circular. They can’t carry as much oxygen, which can leave tissues oxygen deprived (anemia) = pain! The disease is recessive, but co-dominant because heterozygotes also have a mild form of the disease. SS= No disease Ss = Sickle Cell Trait (mild form) ss= Sickle Cell

Codominance NS = some of each SS = sickle cells NN = normal cells sick The heterozygous condition, both alleles are expressed equally Sickle Cell Anemia in Humans NS = some of each SS = sickle cells NN = normal cells sick

Problem: Codominance S NS SS N S GENOTYPES: - NS (2) SS (2) Show the cross between an individual with sickle-cell anemia and another who is a carrier but not sick. N S GENOTYPES: - NS (2) SS (2) - ratio 1:1 S NS SS PHENOTYPES: - carrier (2); sick (2) - ratio 1:1

Summary What is Codominance? What is incomplete dominance When two dominant traits both show up at the same time. What is incomplete dominance When two traits BLEND and neither is dominant.

PURE GOLD Breeding a pure brown with a pure white… BB x WW W W B BW BW Genotype % BB % WW % BW W W B BW BW 100 Phenotype % Brown % White % Palomino BW BW 100

Coat color genes in mammals Multiple Genes Coat color genes in mammals

More complications Polygenic traits- determined by effects of two or more genes Pleiotropy- gene has multiple effects on phenotype Epistasis - one gene affects the expression of another Phenotypic plasticity – environment influences phenotype

Epistatic effect of locus C on locus B Allele C permits synthesis of dihydroxyindole cc can’t make dihydroxyindole Locus B enzyme converts brown dihydroxyindole to black eumelanin

Phenotypic plasticity soil pH affects Hydrangea flower color