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Incomplete Dominance. Neither allele is completely dominant over the other allele. The phenotype is heterozygous A mixture or blending of the two What two colors do you think blended to make grey?. Incomplete Dominance Ex: Four-o’ clock flowers. Neither Red (R)
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Incomplete Dominance • Neither allele is completely dominant over the other allele. • The phenotype is heterozygous • A mixture or blending of the two What two colors do you think blended to make grey?
Incomplete DominanceEx: Four-o’ clock flowers • Neither Red (R) • or White (W) is dominant • When a homozygous red flower (RR) mixes with a homozygous white flower (WW), the alleles blend in the hybrid (RW) to produce pink flowers
How to Recognize Incomplete Dominance….. • The offspring is showing a 3rdphenotype (red flower, white flower, and pink flower) • The trait in the offspring is a blend (mixing) of the parental traits (red x white = pink)
Incomplete Dominance Practice Problems • A cross between a blue blahblah bird and a white blahblah bird produces offspring that are silver. The color of blahblah birds is determined by just two alleles. • What are the genotypes of the parent blahblah birds in the original cross? • What is/are the genotypes of the silver offspring? • What would be the phenotypic ratios of offspring produced by two silver blahblah birds?
Incomplete Dominance Practice Problems • In northeast Kansas there is a creature know as a wildcat. It comes in three colors, blue, red, and purple. This trait is controlled by a single locus gene with incomplete dominance. A homozygous (BB) individual is blue, a homozygous (bb) individual is red, and a heterozygous (Bb) individual is purple. What would be the genotypes and phenotypes of the offspring if a blue wildcat were crossed with a red one?
Incomplete Dominance Practice Problems Coat color in mice is incompletely dominant. Yellow and white-colored mice are homozygous, while cream-colored mice are heterozygous. If two cream-colored mice mate, what phenotypic ratio can we expect of their offspring?
Codominance • Two equally dominant alleles are expressed at the same time. • Heterozygous phenotype will have both phenotypes visible
Codominance • Ex; Short Horn Cattle • Homozygous red (RR) • Homozygous white (WW) The offspring of will have both red and white hairs (RW) The offspring are heterozygous and called “roan”
Codominance Practice Problems A cross between a black cat and a tan cat produces a tabby pattern (black & tan fur together). What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?
Codominance Practice Problems Roan cattle are the heterozygous hybrids of a cross between a white bull and a red cow. If a roan bull were crossed with a red cow, what would be the possible phenotypes of their offspring?
Human Blood types ABO are examples of codominace. Blood types come from three different alleles and therefore are considered a multiple trait allele. The multiple trait alleles are: I , I , and i. I and I both result in an antigen on the surface of red blood cells however; i is recessive and does not have an antigen. An antigen stimulates the production of antibodies. Codominance A B A B
Sickle- Cell Anemia • Co- dominance • Caused by an abnormal Hemoglobin, the protein that red blood cells use to carry oxygen • Normal hemoglobin is (RR) • Sickle Cell shaped blood cells (SS) • People who are carriers (heterozygous) for the disease there is a mixture of both normal and sickle cell (RS)
Problem: Codominance Show the cross between an individual with sickle-cell anemia and another who is a carrier but not sick. Remember: RR = normal RS = carrier of sickle cell SS = sickle cell
Problem: CodominanceBlood Types Mrs. Clink is type “A” and Mr. Clink is type “O.” They have three children named Matthew, Mark, and Luke. Mark is type “O,” Matthew is type “A,” and Luke is type “AB.” Based on this information: Mr. Clink must have the genotype ______ Mrs. Clink must have the genotype ______ because ___________ has blood type ______ Luke cannot be the child of these parents because neither parent has the allele _____.
Problem: CodominanceBlood Types Two parents think their baby was switched at the hospital. Its 1968, so DNA fingerprinting technology does not exist yet. The mother has blood type “O,” the father has blood type “AB,” and the baby has blood type “B.” Mother’s genotype: _______ Father’s genotype: _______ Baby’s genotype: ______ or ________ Punnett square showing all possible genotypes for children produced by this couple Was the baby switched?
Partner Work Find a friend or two and work the following genetic problems. Have fun and focus on the task “at hand”!
PRACTICE QUESTIONS 1. In a certain case a woman’s blood type was tested to be AB. She married and her husband’s blood type was type A. Their children have blood types A, AB, and B. What are the genotypes of the parents? What are the genotypic ratios of the children?
2. In a certain breed of cow, the gene for red fur, R, is codominant with that of white fur, W. What would be the phenotypic & genotypic ratios of the offspring if you breed a red cow and a white bull? What would they be if you breed a red & white cow with a red & white bull?
3. A rooster with grey feathers is mated with a hen of the same phenotype. Among their offspring 15 chicks are grey, 6 are black and 8 are white. a. What is the simplest explanation for the inheritance of these colors in chickens? b. What offspring would you expect from the mating of a grey rooster and a black hen?
