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Complex Patterns of Inheritance

Complex Patterns of Inheritance. Beyond Mendel’s rules of simple dominant/recessive inheritance. Incomplete Dominance. Neither allele is dominant; heterozygote is a blend of phenotypes of the two homozygotes. Red + White = Pink. Genotype = CC; phenotype = chestnut.

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Complex Patterns of Inheritance

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  1. Complex Patterns of Inheritance Beyond Mendel’s rules of simple dominant/recessive inheritance

  2. Incomplete Dominance Neither allele is dominant; heterozygote is a blend of phenotypes of the two homozygotes. Red + White = Pink

  3. Genotype = CC; phenotype = chestnut

  4. Genotype = WW; phenotype = white

  5. Genotype = CW; phenotype = palomino

  6. Practice incomplete dominance with Four O’Clocks (flowers) P = RR x WW Red parent plant R R W RW RW White parent plant RW RW W Genotype of F1 = 100% RW All pink! Phenotype of F1 =

  7. F1 = RW x RW Pink parent plant R W R RR RW Pink parent plant RW WW W Genotype ratio of F2 = 1RR : 2RW: 1WW 1 red : 2 pink: 1 white Phenotype ratio of F2 =

  8. Codominance Both alleles are dominant; expressed separately Red + White = Both Red and White (NOT pink!)

  9. Genotype: RW

  10. Genotype = RR; phenotype = red

  11. Genotype = WW; phenotype = white

  12. Genotype = RW; phenotype = roan

  13. Show the cross between two roan cows (use R and W). • What is the probability that two roan cows will have at least one roan offspring? 50% • What is the probability that two roan cows will have a white offspring? 25% R W RR RW R WW W RW

  14. Multiple Alleles More than 2 alleles possible for a trait • Example: Blood type in humans • Three alleles possible (A, B, and O), each person only has two of those alleles • Four phenotypes (blood types) possible: A, B, AB, and O • A and B are codominant; O is recessive • Alleles notated as IA, IB, i

  15. Type A: IAIA or IAi Type B: IBIB or IBi Type AB: IAIB Type O: ii Notice the new allele notation!

  16. Polygenic Traits Trait is controlled by interaction between 2 or more genes • Examples: skin color, eye color, height, hair color • Results in a continuum of expressed phenotypes

  17. Lethal Recessive Alleles • Having two mutated copies of an essential gene may be deadly • E.g., Cystic Fibrosis, Sickle-cell Anemia, Tay-Sachs Disease • Heterozygote survivse because it has one nonmutated form of the gene • Heterozygote is carrier for disorder • Heterozyous condition is sometimes linked with beneficial traits • e.g., sickle cell carrier and malaria resistance

  18. Other Complex inheritance patterns still to come: • Sex-linked traits • More about blood • Environmental effects • Chromosomal disorders

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