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Ch. 7

Ch. 7. Extending Mendelian Genetics. Review. Genotype: alleles that are present Phenotype: physical appearance. Rr RR rr If Red is dominant to white, what is the phenotype of the above?. Vocab to Remember!. Allele Gene Trait Dominant Recessive Mendel Autosomes Sex Chromosomes

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Ch. 7

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  1. Ch. 7 Extending Mendelian Genetics

  2. Review • Genotype: alleles that are present • Phenotype: physical appearance • Rr • RR • rr • If Red is dominant to white, what is the phenotype of the above?

  3. Vocab to Remember! • Allele • Gene • Trait • Dominant • Recessive • Mendel • Autosomes • Sex Chromosomes • And so forth . . .

  4. 7.1 Autosomes • Any chromosome other than the sex chromosomes • How many are there in a diploid human cell?

  5. Recessive Alleles • Only seen when there is no dominant allele present • Ex: • Homozygous recessive • Sex linked

  6. Recessive Disorder • Caused by recessive allele • Must not have any dominant alleles in order for disorder to show up • More common

  7. Autosomal Recessive Disorders • On autosomes NOT sex chromosomes • Affects both males and females equally • Why? • Which pairs could be affected on the right?

  8. Carriers • Heterozygous • Have 1 recessive allele • Appear “normal” • Show no symptoms • Can pass recessive allele on • Offspring could have disease

  9. Which Crosses? • . . . Could produce an affected individual? • This one? • How about this one? • And this one????

  10. Dominant Disorder • Caused by dominant allele • Only need one allele for disorder to present • Far less common

  11. Sex Linked Traits • Genes are located on sex chromosomes NOT on autosomes • X chromosome is larger • Holds more info than Y • Has more influence on phenotype • ~1000 genes on X • ~78 on Y • Which chromosomes are sex linked?

  12. Sex-Linked Gene Expression • Different than autosomal • Whatever is carried on the X chromosome is expressed in males. . . • WHY? • Males – XY • Females - XX

  13. Here Kitty, Kitty . . . • Why are calicos always females? • Has to do with the X chromosome. . .

  14. X Chromosome Inactivation • One X chromosome coils VERY tightly • Becomes inactivated • Not expressed • Causes Calico coloration in cats • Alleles expressed randomly across their body

  15. 7.2 Complex Patterns of Heredity • Polygenic traits • Multiple alleles • Incomplete dominance • Codominance

  16. Mendelian Genetics • Had only two possible phenotypes • Explains some traits • BUT not all . . . • Some traits are more complicated

  17. Incomplete Dominance • Intermediate form • No dominant • No recessive • Heterozygous individual is different from either parent • Produces a new phenotype

  18. Incomplete Dominance • Ex: • Primroses • Four-o-clocks • Snapdragons • Betta fish

  19. Incomplete Dominance • Sometimes written using different letters: • Red = RR • White = WW • Thus: Pink = RW • Or using subscripts: • R1R1 = Red • R2R2 = White • R1R2 = Pink

  20. Incomplete Dominance • Why? • The single "red" allele is unable to code for the production of enough red pigment to make the petals dark red

  21. Betta Fish • Green = homozygous = B1B1 • Steel Blue = homozygous = B2B2 • Royal Blue = heterozygous = B1B2

  22. Codominance • Neither allele is dominant nor recessive • Heterozygous display both traits • Both alleles are expressed completely but separately • Ex: • Blood type AB • Flower colors (some)

  23. Multiple Alleles • Genes with three or more alleles • = Possiblealleles • But REMEMBER: • only inherit two • One from each parent • Ex: • Human blood type

  24. Blood Type • More complicated: • Multiple alleles • Codominance • Dominant/recessive • Determined by presence of antigens (protein) on blood cells • A antigen • B antigen • O = no antigens

  25. Blood Type: • If a person receives an A allele and a B allele, their blood type is type AB • What if they gat an A and an A?

  26. Human Blood Types • Controlled by 3 alleles • Four possible phenotypes: A, B, AB, and O • O is recessive • A and B are codominant

  27. ABO Blood Types

  28. Human Blood Types

  29. Polygenic Traits • Influenced by severalgenes • May be on same or different chromosome • Many combinations occur in offspring • Degrees of intermediate conditions

  30. Polygenic Traits • Ex: • Eye color • Height • Weight • Hair color • Skin color

  31. Epistasis • When a gene interferes with the expression of other genes • Ex: • Albinism – a gene blocks production of pigments • Skin, hair, and eyes = light

  32. Traits and the Environment • Phenotype often depends on the environment • Ex: Hydrangea flowers • In acidic soil bloom blue • In basic soil bloom pink

  33. Traits and the Environment • Ex: Arctic fox • Temperature affects pigment production gene • In summer – pigment made • In winter-no pigment made

  34. Traits and the Environment • Ex: Siamese cats • Temperature affects fur color • Cooler regions of body = darker fur

  35. Traits and the Environment • Ex: Turtles • Sex determined by temperature • Warm temperature = females • Cooler temperature = males

  36. 7.3 Gene Linkage • Genes that tend to be inherited together = linked • First described by • William Batesonand R.C. Punnett(also invented Punnett Square) • Studied dihybrid crosses in peas

  37. Thomas Hunt Morgan • 1886-1945 • Studied fruit flies • = Drosophila melanogaster • Determined chromosomes made up of genes • Sex-linked traits were discovered

  38. Linkage Maps • Show relative location between linked genes • First made by Alfred Sturtevant, a student of Morgan’s • Used crossing over frequencies

  39. 7.4 Pedigree • Shows how a trait is inherited over several generations • A chart • Symbols represent people • Lines represent relationships • Allows us to “see” disorder quickly

  40. Pedigree Basics:

  41. Autosomal Recessive Trait • Allele located on autosome • Affects both males and females • Recessive = only shows up if homozygous recessive!

  42. Autosomal Dominant Trait • Allele located on autosome • Affects both males and females • Dominant = if present allele it is expressed!

  43. Sex-linked Traits-Recessive • Allele located on sex chromosome • On X chromosome • Affects mostly males

  44. Determine the Type of Trait • Autosomal or sex-linked? • Dominant or recessive? • How can we tell?

  45. Albinism • Determine the genotypes of individuals:

  46. Genetic Disorders • Harmful effects produced by inherited mutations • Many carried by recessive alleles • Carriers • Heterozygous (Ex: Tt) • Appear normal • Carry a recessive gene • Can pass it on

  47. Human Genetic Disorders • Ex: Sickle Cell Anemia • Recessive • Affects blood • Produces defective hemoglobin • Carries oxygen • Found in RBC

  48. Sickle Cell Anemia • Causes many RBC’s to bend • Become sickle-shaped • Cells rupture easily and get stuck in vessels • Blocks blood flow • Not enough oxygen

  49. Sickle Cell Anemia • Interesting fact: • If Heterozygous: • Protected from malaria! • Sickled cells kill protist that causes malaria • Still have enough normal cells to carry oxygen

  50. Human Genetic Disorders • Ex: Cystic Fibrosis • Recessive • Most common in Caucasians • 1 in 25 Caucasians = carriers • 1 in 2,500 Caucasian infants = homozygous recessive • = disorder

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