INCOMPLETE DOMINANCE

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1 DOMINANCE

2 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.

3 Snapdragons HUH?

4 Incomplete Dominance R 1 F 1 X R 2 R 2 R 2 does not produce pigment F 2 Heterozygote only produces ½ pigment of R 1 R 1

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6 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.

7 Roan Horse

8 Roan Cattle Variegated Clover

9 MULTIPLE ALLELISM When there is more than 2 alleles possible for a given gene. Allows for a larger number of genetic and phenotypic possibilities.

10 CODOMINANCE & MULTIPLE ALLELES

11 BLOOD TYPES 4 ABO blood types 3 alleles of the I gene I A = A antigen on RBC I B = B antigen on RBC i = neither A nor B antigen Genotype I A I A or I A i I B I B or I B i I A I B ii Blood type A B AB O Antibody Anti B Anti A None Anti A, Anti B

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16 Codominance & Multiple Alleles BLOOD TYPE A B AB I A I B GENOTYPE CAN RECIVE BLOOD FROM I A I A, I A i A, O I B I B, I B i B, O O ii O A, B, AB, O Human blood type is an example of both codominance and a trait with multiple alleles. AB = universal acceptor O = universal donor

17 Rhesus Factor The Rhesus factor, also known as the Rh factor, gets its name from experiments conducted in 1937 by scientists Karl Landsteiner and Alexander S. Weiner. Involved Rabbits which when injected with the Rhesus monkey s red blood cells, produced an antigen present in the red blood cells of many humans

18 Rhesus Factor The Rhesus factor is an antigen, or more specifically a protein, that exists on the surface of red blood cells. If a person has either two (+) genes for Rh or one (+) and one (-) Rh gene, they will test Rh(+). A person will be negative only if they have 2 (-).

19 Relevance of Rh Factor & ABO Typing? It is very important in terms of babies: E.g. an Rh(-) mother may make antibody against an Rh(+) fetus if the baby gets a (+) gene from its father (Obstetricians screen pregnant women for this problem with blood tests). The ABO and RH genes are only two of many blood antigens that are present on human red cells and must be matched up for successful blood transfusions.

20 Multifactorial Referring to control of the expression of a trait by several genes and environmental factors. Many multifactorial traits show continuous distribution.

21 Multifactorial E.g. Human height à usually between 120cm and 200cm, however these genes cannot be fully expressed without all the necessary nutrients from a healthy diet

22 Sex Linked Traits X-linked recessive traits expressed in the phenotype of men. This is due to the fact that men only have one X chromosome. In women, a recessive allele on one X chromosome is often masked in their phenotype by a dominant normal allele on the other. women are frequently carriers of X-linked traits but more rarely have them expressed in their own phenotypes.

23 Examples Duchenne Muscular Dystrophy Hemophilia Red-Green Color Blindness Male Pattern Baldness

24 If a woman is a carrier of an X-linked recessive allele for a disorder and her mate does not have it, their boys will have a 50% chance of inheriting the disorder. None of their girls will have it, but half of them are likely to be carriers. dominant allele = A recessive allele = a

25 If a man has an X- linked recessive disorder and his mate does not carry the allele for it, all of their girls will be carriers. None of their boys will inherit the harmful allele. Only girls receive X chromosomes from their fathers.

26 PRACTICE QUESTIONS 1. In a certain case a woman s blood type was tested to be AB. She married and her husbands 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?

27 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?

28 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?