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Unit 6: Inheritance

Unit 6: Inheritance. Part 2: Complex Patterns of Inheritance. Extending Mendelian genetics. Mendel worked with a simple system peas are genetically simple most traits are controlled by single gene each gene has only 2 versions 1 completely dominant ( A ) (complete dominance)

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Unit 6: Inheritance

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  1. Unit 6: Inheritance Part 2: Complex Patterns of Inheritance

  2. Extending Mendelian genetics • Mendel worked with a simple system • peas are genetically simple • most traits are controlled by single gene • each gene has only 2 versions • 1 completely dominant (A) (complete dominance) • 1 recessive (a) • Examples: albinism, earlobes, tongue rolling • But it’s usually not that simple!

  3. Packet p. 11 Practice on 12 Incomplete dominance • Hybrids have “in-between” appearance • FRFR = red flowers • FrFr = white flowers • FRFr = pink flowers • make 50% less color FRFR FRFr FrFr In humans, hypercholesterolemia is an example of incomplete dominance. CHCH= normal CHCh= elevated cholesterol (2x’s the normal level ChCh= extremely high cholesterol (5x’s the normal level, VERY dangerous).

  4. Packet p. 11 Practice on 12 & 13 Codominance (& multiple alleles) • Equal dominance (expressed equally) • human ABOblood groups • 3 versions • IA, IB, i • A& B alleles are codominant • both A& B alleles are dominant over i allele • the genes code for different carbohydrate "flags" on the surface of red blood cells

  5. Blood donation clotting clotting clotting clotting clotting clotting clotting

  6. Pleiotropy • One gene can have many effects. • eg sickle cell

  7. Packet p. 11 Many genes: one character • Polygenic inheritance • additive effects of many genes • humans • skin color • height • eye color • intelligence • behaviors

  8. Polygenic inheritance • Multiple genes affect one trait. • Human skin color is controlled by at least 3 genes, each with at least two alleles. • This Punnett square shows the potential offspring skin tones in the F2 generation, crossing two individuals who are triple heterozygotes.

  9. Polygenic inheritance • Eye color is controlled by 4 known genes and probably multiple others • At least 3 pigment genes • Brown (B) dominant to blue (b) and to G & g (below) • Green (G) dominant to blue (g) • Melanin • At least 1 structural gene

  10. Linked genes • So far we have talked about independent assortment, which is… • But, some genes ARE inherited together • On autosomal chromosomes, we call these linked genes • On sex chromosomes, we call these sex-linked genes

  11. Sex-linked genes • X-linked • Recessive: hemophilia, red-green colorblindness • Recessive traits are more common in males. Why? • There are very few disorders that are X-linked dominant. Why do you think?

  12. Pedigrees • Pedigrees are family trees that show the presence/absence of specific traits or diseases. • Squares represent males • Circles represent females • Filled shapes represent the presence of a trait or disease • Some pedigrees show carriers (half-filled shapes) If this pedigree tracks the presence of an autosomal homozygous recessive trait, what are the genotypes of the very first parents at the top?

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