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Genetics

Genetics. Terminology. Allele – contrasting form of a gene Ex: T = tall; t = short Ex: G = green; g = yellow CAPITAL LETTERS – DOMINANT TRAIT lowercase letters – recessive trait. More Terms. Genotype Genetic makeup of an organism Phenotype Physical appearance. More Terms.

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Genetics

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  1. Genetics

  2. Terminology • Allele – contrasting form of a gene • Ex: T = tall; t = short • Ex: G = green; g = yellow • CAPITAL LETTERS – DOMINANT TRAIT • lowercase letters – recessive trait

  3. More Terms • Genotype • Genetic makeup of an organism • Phenotype • Physical appearance

  4. More Terms • Homozygous Alleles • when the alleles of a pair are the same • Ex: GG, TT, rr, nn • Heterozygous Alleles • when the alleles are not the same • Ex: Gg, Tt, Rr, Nn

  5. Probability • The likelihood that a specific event will occur Probability = ----------------------------- # of one kind of event # of all events

  6. Coin Toss • Probability of a coin landing heads up? • The more times you flip the coin, the closer to 50% the probability will get

  7. Punnett Squares • Device used in predicting possible offspring

  8. Monohybrid Cross • A cross that involves only one trait with two phenotypes • Ex: Seed color • GG x gg; • G = green, g = yellow

  9. Making a Punnett Square • Draw a box • Put one set of traits on top • Male parent • Put the other on the side • Female parent

  10. Parent Generation: P1 GG x gg G G g Gg Gg Gg Gg g

  11. Cross F1 Generation • Gg x Gg • Genotype? • Phenotype?

  12. Parent Generation: F1 Gg x Gg g G Gg GG G Gg gg g

  13. Results • Genotypes • 25% GG • 25% gg • 50% Gg • Phenotypes • 75% green • 25% yellow g G G Gg GG g Gg gg

  14. You Try • TT x Tt (T = tall; t = short)

  15. TT x Tt (T = tall; t = short) • Genotypes • 50% TT • 50% Tt • 1:1 • Phenotypes • 100% tall T T T TT TT t Tt Tt

  16. You Try You Try • Bb x bb (B = black; b = white)

  17. Bb x bb (B = black; b = white) • Genotypes • 50% Bb • 50% bb • 1:1 • Phenotypes • 50% black • 50% white • 1:1 b B bb Bb b bb b Bb

  18. Testcross • A cross between a homozygous recessive individual and an unknown • Used to determine whether an individual is homozygous dominant or heterozygous

  19. Testcross • Mendel developed what is known as a test cross. • He took a homozygous recessive individual and mated it with a pea plant showing the dominant trait. bb x Bb or BB

  20. Testcross • If in the F1 generation all the offspring showed the dominant trait, then the dominant parent was probably BB. b b Bb B Bb ? Bb Bb B

  21. Testcross • If there were any recessives in the F1, then the dominant parent had to be Bb. b b Bb Bb B ? bb bb b

  22. What if we are looking at two traits at a time?

  23. What if we are looking at Tall plants with Axial flowers (TTAA) and cross it with a short plant with terminal flowers (ttaa)?

  24. If we look at meiosis what does that tell us? T T A T A T A A Parent TTAA

  25. Parent TTAA can only pass on the alleles TA to the offspring • What about Parent ttaa? • Can only pass on the alleles ta to the offspring

  26. Parents: TTAA x ttaa Parent TTAA produces only one kind of gamete. Parent ttaa produces only one kind of gamete. Thus our punnett square is very simple. TA ta TtAa

  27. What about the F1 generation? T T A t t A T A a t a Parent TtAa a

  28. F1 generation: TtAa x TtAa Ta ta tA TA TA TA TTAA TtAA TtAa TTAa Ta TTAa Ttaa TTaa TtAa TtAa ttAA ttAa tA TtAA ta TtAa Ttaa ttAa ttaa

  29. Dihybrid Cross • A cross with two traits • Ex: seed color & seed shape • R = round, r = wrinkled; Y = yellow, y = green • RRYY x rryy • YYRr x yyRR

  30. Dihybrid Cross You try RRYY x rryy R = round, r = wrinkled; Y = yellow, y = green

  31. Parents: RRYY x rryy All offspring will be heterozygous RY RrYy ry

  32. Dihybrid Cross You try F1 generation: RrYy x RrYy R = round, r = wrinkled; Y = yellow, y = green

  33. F1 generation RrYy x RrYy

  34. F1 generation: RrYy x RrYy • Phenotypes • Round: Yellow • Round: Green • Wrinkled: Yellow • Wrinkled: Green • 9:3:3:1 ratio 9 3 3 1

  35. Sex-linked Genes • Genes carried on the X and Y chromosomes are called sex-linked genes. • Traits that are controlled by these genes occur more often in one sex than the other. • Can you explain why?

  36. Sex-linked Genes • Colorblindness is one example of a trait controlled by sex-linked genes.

  37. Color blindness • The normal human retina's color receptors are tuned to green, blue, and red. Working together, the three give us our colorful view of the world. When one or more of those color receptors is missing the result is color-blindness. The genes for our red and green color receptors are located on the X-chromosome, giving women a redundant set of receptor genes. This is why men are far more prone to color-blindness than women.

  38. Sex-linked Genes XCY x XX Recessive gene for color blindness

  39. Sex-linked Genes Y XC XCX XY X XY XCX X

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