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Chapter 14

Chapter 14 . Genetics. Introduction. Pre 1800s – blending hypothesis 1850s – Gregor Mendel. Pisum sativum – what makes pea good genetic model? - - - - Pea character (gene) = Pea trait (allele) = . self fertilization Vs. cross fertilization. The monohybrid cross.

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Chapter 14

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  1. Chapter 14 Genetics

  2. Introduction • Pre 1800s – blending hypothesis • 1850s – Gregor Mendel

  3. Pisumsativum– what makes pea good genetic model? - - - - • Pea character (gene) = • Pea trait (allele) =

  4. self fertilization Vs. cross fertilization

  5. The monohybrid cross • Cross true breeding parental plants (P) • produces F1 generation

  6. -character (gene)-trait (allele)- dominant phenotype- recessive phenotype

  7. F1 plants all purple

  8. Cross F1 plants F2 plants = ~250 white ~750 purple A monohybrid Is this quantitative or qualitative data?

  9. Mendel’s Conclusions

  10. Dominance Allele = Alternative version of gene Dominant allele P Recessive allele p Each individual inherits 2 alleles/gene Genotype Phenotype? PP homozygous dominant pp homozygous recessive Pp heterozygous

  11. Dominant allele masks expression of recessive allele Find the dominant allele Pick symbols What is the phenotype of plant with genotype Rr? What is genotype of a green plant?

  12. Genotype?

  13. Segregation • The 2 alleles segregate in gametes during meiosis • Random segregation Pea chromosome 1 Genotype of plant? Phenotype of plant? Human chromosome 11 gene for beta globin Genotype Hbb/Hbb

  14. Mendel did not know about: • DNA/chromosomes/genes • Crossing over or the cell cycle • Linked alleles

  15. In mice, black fur is dominant over white fur Cross heterozygous mouse with homozygous recessive mouse Possibilities?

  16. In mice, black fur is dominant over white furCross heterozygous mouse with homozygous recessive mouse • Make an allele key • Show the cross 3. Write the phenotypes under the genotypes 4. Determine the parental gametes (random segregation) 5. Add to Punnett square 6. Determine offspring

  17. Punnett square What is the expected ratio of phenotypes? Genotypes? In a litter of 3, how many are expected to be white? Which phenotype is the recessive phenotype?

  18. In cats striping is dominant over non-stripes. Mate two heterozygous cats.

  19. The Scottish fold is a dominant trait Genotypes FF Ffff Phenotypes? The original Scottish Fold was a white barn cat named Susie, found in Scotland

  20. Test cross Scottish fold cat -> Is she Ff or FF? If FF, then cross toff kittens? If Ff, then cross to ff  kittens? A test cross is always a cross to a homozygous individual.

  21. Review • All possible one gene crosses B = black fur allele b = white fur allele • BB X BB  all black • BB X Bb  • BB X bb  • Bb X Bb  • Bb X bb  • bb X bb  all white

  22. The Dihybrid cross (2 genes)

  23. Independent Assortment 2 genes Y = yellow pea allele R = round pea allele y = green pea allele r = wrinkled Phenotypes of peas

  24. X RRYY rryy True-breeding yellow, round X true-breeding green, wrinkled Allele key? P Genotype? Gametes? (always 4 per parent in 2 gene cross) R = round allele Y = yellow r = wrinkled y = green RY and ry

  25. Parental generation: RRYY X rryy Gametes ? F1 generation? Gametes of F1 generation? F2 generation?

  26. F2 generation Ratio of genotypes? Ratio of phenotypes?

  27. Extensions of Mendel Codominance Both alleles expressed in phenotype Ex. Blood type I gene Alleles IA IB Phenotype of IA IB ?

  28. multiple alleles Ex. blood type Alleles IA IB i IAIA IBIB IA IB IAiIBi ii

  29. polygenic inheritance multiple genes affect characteristic Ex. skin – at least 3 genes Height

  30. environmental effects A particular genotype may have a phenotypic range • Ex • Does blood color have a norm? • Skin color?

  31. ?

  32. Recessively inherited disorders A allele  normal protein a allele  malfunctioning or no protein AA Aa heterozygotes are carriers aa disorders range from fetal lethal to mild

  33. Ex. albinism a allele does not code for functional melanin protein Chromosome 11

  34. Recessive traits bb = blond hair bb = blue eyes ii = type O blood

  35. Dominantly inherited disorders A allele  abnormal protein a allele  normal protein AA Aa aa

  36. Achondroplasia D allele causes dwarfism

  37. Multifactorial disorders Genetic component + environment (aging, diet, chemicals, radiation, etc.)

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