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Genetics and Heredity II

Genetics and Heredity II. Complete Dominance. The dominant allele completely masks the recessive allele in the heterozygous condition Example: RR = red Rr = red rr = white. Complete Dominance.

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Genetics and Heredity II

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  1. Genetics and Heredity II

  2. Complete Dominance • The dominant allele completely masks the recessive allele in the heterozygous condition • Example: RR = red Rr = red rr = white

  3. Complete Dominance • Free earlobes are dominant to attached earlobes. Complete a punnett square for a cross between a heterozygous free earlobed person and a person with attached earlobes. What is the probability that they will have a child with attached earlobes?

  4. Incomplete Dominance • The dominant allele is partially expressed resulting in an blended phenotype in the heterozygous condition • Ex: RR = red RW = pink WW = white

  5. Incomplete Dominance • In snapdragons, flower color is controlled by incomplete dominance. The two alleles are red (R) and white (W). The heterozygous genotype is expressed as pink. If you cross two pink flowered plants, what is the probability that you will get a red flowered plant? Use a punnett square to answer.

  6. Codominance • Both alleles in a gene pair are fully expressed resulting in a heterozygous offspring showing both traits • Ex: RR = red RW = red and white WW = white

  7. Codominance ABO system of blood types This is an example that uses a 3 allele system. A persons blood type is based on the absence or presence of certain proteins in their red blood cells. A is codominant with B- neither covers the other and both are expressed independently. A is dominant over O- Only A is expressed if A and O are present. B is dominant over O- Only B is expressed if B and O are present. Possible genotypes Phenotypes AA --------------------------- Type A AO --------------------------- Type A BB --------------------------- Type B BO --------------------------- Type B AB --------------------------- Type AB OO --------------------------- Type O

  8. Codominance • If a person with AB blood type married a person with the O blood type, what is the probability that they would have a child whose blood type is A? (use a punnett square)

  9. Polygenic Trait • Characteristic that depends on the alleles from two or more genes • Ex: height, hair color, eye color, skin color

  10. Sex-linked Trait • Traits carried on the sex chromosomes (X and Y in humans) • Examples: hemophilia, Duchenne muscular dystrophy, fragile-X syndrome, some high blood pressure, congenital night blindness, red-green color blindness, “male pattern baldness". 

  11. Sex-linked Traits • Hemophilia is an X-linked recessive trait. If a person has a copy of the hemophilia gene and a copy of the dominant non-hemophilia gene is not present, the person will have the disease. If a man is normal, and a woman carries the hemophilia gene, what is the probability that the couple will have a daughter with hemophilia? What is the probability that they will have a son with hemophilia?

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