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Beyond Mendel’s Laws of Inheritance

Beyond Mendel’s Laws of Inheritance. Incomplete dominance. Hybrids have “in-between” appearance RR = red flowers rr = white flowers Rr = pink flowers make 50% less color. 100% pink flowers. 1 st generation (hybrids). 100%. 25% red. 50% pink. 25% white. 1:2:1. 2 nd

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Beyond Mendel’s Laws of Inheritance

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  1. Beyond Mendel’s Lawsof Inheritance

  2. Incomplete dominance • Hybrids have “in-between” appearance • RR = red flowers • rr = white flowers • Rr = pink flowers • make 50% less color

  3. 100% pink flowers 1st generation (hybrids) 100% 25% red 50% pink 25% white 1:2:1 2nd generation Incomplete dominance true-breeding red flowers true-breeding white flowers X self-pollinate

  4. 25% 25% male / sperm R W 50% 50% 25% 25% Incomplete dominance RW x RW % genotype % phenotype RR RW female / eggs RW WW 1:2:1 1:2:1

  5. Codominance • Equal dominance • human ABOblood groups • 3 version • A, B, i • A& B alleles are codominant • both A& B alleles are dominant over i allele • the genes code for different sugars on the surface of red blood cells • “name tag” of red blood cell

  6. Sex chromosomes

  7. Sex-linked Traits • Sex chromosomes have other genes on them, too • especially the X chromosome • hemophilia in humans • blood doesn’t clot • Duchenne muscular dystrophy in humans • loss of muscle control • red-green color blindness • see green & red as shades of grey X X X Y

  8. Sex-linked traits XHXh XH Xh male / sperm XH Y XHXH XHY XH female / eggs Xh XhY XHXh 2 normal parents, but mother is carrier XH XHY male / sperm Y

  9. One gene: many effects • most genes are affect many traits • 1 gene affects more than 1 trait • dwarfism (achondroplasia) • gigantism (acromegaly)

  10. Acromegaly: André the Giant

  11. Many genes: one trait • Polygenic inheritance • additive effects of many genes • humans • skin color • height • weight • eye color • intelligence • behaviors

  12. Human skin color • AaBbCc x AaBbCc • can produce a wide range of shades • most children = intermediate skin color • some can be very light & very dark

  13. Albinism

  14. Coat color in other animals • 2 genes: E,eandB,b • color (E) or no color (e) • how dark color will be: black (B) or brown(b)

  15. Environment effect on genes • Phenotype is controlled by both: environment & genes Human skin color is influenced by both genetics & environmental conditions Coat color in arctic fox influenced by heat sensitive alleles Color of Hydrangea flowers is influenced by soil pH

  16. Dominant ≠ most common allele • Because an allele is dominant does not mean… • it is better, or • it is more common

  17. Polydactyly individuals are born with extra fingers or toes the allele for >5 fingers/toes is DOMINANT & the allele for 5 digits is recessive recessive allele far morecommon than dominant  only 1 individual out of 500 has more than 5 fingers/toes  so 499 out of 500 people are homozygous recessive (aa)

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