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14b

14b. Extending Mendelian Genetics. Incomplete dominance. F1 hybrids appearance is an ______________ of the 2 parental phenotypes. Ex: snapdragons  red X white = pink Genotype ratio: Phenotype ratio:. R. r. R. r. Complete dominance.

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14b

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  1. 14b Extending Mendelian Genetics

  2. Incomplete dominance • F1 hybrids appearance is an ______________ of the 2 parental phenotypes. • Ex: snapdragons red X white = pink Genotype ratio: Phenotype ratio: R r R r

  3. Complete dominance • Dominant homozygous and __________ and indistinguishable (ex. Mendel’s peas)

  4. Codominance • Both alleles are separately manifest in the phenotypes. • Ex. Human blood groups ___________

  5. Genetic Diseases • 1. Tay-sach’s: brain cells unable to metabolize certain lipids due to defective enzyme. Lipid accumulation can lead to death. • TT normal enzymes ____________ • Tt ½ normal, ½ defective enzymes ___________ • tt defective enzyme:

  6. Dominant does not subdue recessive!! • Ex. Round vs. wrinkled seeds: • dominant: enzyme that converts sugar to starch • Recessive: defective enzyme, sugar accumulation, takes in ______and swells, dries and ___________ • If dominant allele is present, enzyme can convert sugar to starch, therefore dominant homozygous has same phenotype as ____________. • Also important: dominant does not mean more frequent in the population!!

  7. Multiple Alleles • Ex. A, B, AB and O blood types: A or B carbohydrates on red blood cells • 3 alleles: IA IB or i (neither A or B) • 6 possible genotypes (A and B are codominant, i is recessive) • IAIA and IAi are type A (make B antibodies) • IBIB and IBi are type B (make A antibodies) • IAIB are type AB (don’t make antibodies) • ii are type O (make A and B antibodies)

  8. Pleiotropy • A gene affects an organism is many ways • Ex. Alleles for sickle cell anemia cause many symptoms.

  9. Epistasis • Gene at one locust alters the phenotype expression of a gene at a second locus. • Ex. Mice: See paper

  10. Qualitative Characters • Vary among a continuum (not either/or) • Usually polygenic inheritance • Ex. Skin color • AABBCC (very dark)  aabbcc(very light)

  11. Multifactorial Traits • Nature vs nurture: phenotype depends on ____________ as well as ___________. • Study using _____ in different environments. • The phenotypic range possible for a genotype is called the _______ ____ ____________. • Mutifactorial: Many factors, genetic and environment influence phenotype. • Ex:

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