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Chapter 11: Genetics

Chapter 11: Genetics. When told to, put the PTC paper on your tongue. PTC, or phenylthiourea, is an organic compound having the unusual property of either tasting very bitter, or being virtually tasteless, depending on the genetic makeup of the taster.

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Chapter 11: Genetics

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  1. Chapter 11:Genetics

  2. When told to, put the PTC paper on your tongue PTC, or phenylthiourea, is an organic compound having the unusual property of either tasting very bitter, or being virtually tasteless, depending on the genetic makeup of the taster. • The ability to taste PTC is a dominant genetic trait. T = Taster t = non-taster • If you can taste, you are either TT or Tt. • Those who can not taste are tt • About 70% of people can taste PTC, varying from a low of 58% for Aborginal people of Australia to 98% for Native Americans

  3. Ever wonder why people resemble their parents &/or siblings? • How do farmers select the best plants or animals for breeding purposes? • How’d you like that PTC paper? • Why did some people in your class/family taste it and others didn’t?

  4. Genetics • Studies the transmission of traits or characteristics from 1 generation to the next

  5. Gregor Mendel(1822 – 1884)The Father of Genetics • Central European monk (Now the Czech Republic) discovered the basic underlying principles of heredity. • Work completed in 1865 • His work did not get recognized though until 1900 (he was dead by then).

  6. He used pea plants and selectively crossed them over many generations • Saw that certain traits show up in offspring plants without any blending of parent characteristics. X Why all purple?

  7. Mendel's work • Removed the stamen/anther (male parts) to prevent self- pollination 2. Used the stamen from a tall plant and pollinated only flowers from other tall plants 3. Observed generations for 2 years to be certain of purebreds Tall X TallShort X Short Yielded all Talls Yielded all shorts • Crossed plants with contrasting traits Tall X ShortShort X Tall

  8. P = Parental generation • F1 = 1st Filial generation (offspring) • F2 = 2nd Filial generation (next set of offspring off the F1)

  9. P1: Pure Tall X Pure Short T = Tall stems t = short stems TT X tt • F1: Tall (Tt) Only one trait showed • F1 cross: F1Tall X F1Tall Tt Tt • F2: 3 Tall 1 Short TT Tt Tt tt • The “lost” trait reappears!

  10. To get these results for the F2, do FOIL – (firsts, outers, inners, lasts) • *******Always got 75% Tall and 25% short or 3:1 whenever this type of cross occurred.

  11. Mendel’s 4 conclusions (hypotheses) from his experiments 1. Concept of Unit Characters: The inheritance of each trait is determined by “units” or “factors” that are passed on. • We now know these “units” as GENES • These “units” occur in pairs. One from each parent

  12. Law of Dominance: – One factor “masks” the appearance of another factor. It prevents it from showing • Dominant– trait that must show if present (TT or Tt) • Recessive – trait that will only show if in the pure form (tt) • Hybrid – Contains a dominant & a recessive trait (Tt) • Allele– alternate genes for a given trait (Tall allele or short allele)

  13. 3. Law of Segregation • For any trait,pairs of alleles are separated in forming the gametes (during Anaphase I of meiosis). • Only 1 gene (allele) from the pair goes into the gamete during meiosis.

  14. More genetic vocabulary to learn • Genotype: Shows actual genetic makeup. (Use symbols for genes) • TT or Pure dominant or homozygous dominant • Tt or Hybrid or heterozygous • tt or Pure recessive or homozygous recessive Homozygous vs Heterozygous: Pure vs Hybrid (mixed)

  15. Phenotype: • Tells appearance (describes the trait) Tall (if TT or Tt) Short (if tt) • NO HYBRIDS HERE!! • Describe what they look like • For Eye color: • Blue • Green • Brown • For Hair color; Red, Blond or Brown

  16. Dimples Widows peak Mid – digit hair Free earlobe Hitchhikers thumb Chin Dimple 2nd toe larger than 1st Straight pinkie finger

  17. Punnett Squares • Shows possible gene pairing & probability of each pairing. • Checkerboard method • Foiling • During meiosis, when the gametes are formed, the genes of the father and mother separate from each other. This is the law of segregation. T T genes of 1 parent t t genes of 1 parent Phenotype ratio : 100% tall Genotype ratio : 100% Tt (hybrid)

  18. Possible crosses • Do the crosses (Punnett Sqs) & determine the : • Phenotype and Genotype ratios • Trait: T = Tall stem length • t = short stem length • 1. TT x TT •    2. TT x Tt • 3. TT x tt • 4. Tt x Tt • 5. Tt x tt • 6. tt x tt

  19. TT X TT TT X Tt TT X tt Tt x Tt Tt x tt tt x tt

  20. 1. In humans, having a chin dimple is dominant to not having dimples. • Show the cross of two parents who are both hybrid for having dimples. • Give the expected Phenotype ratio and genotype ratio for this cross. ____ = Dimple gene ____ = Non dimple gene Parent cross ______ x ______ Phenotype ratio : Genotype ratio : • For the same trait, cross a hybrid with an individual who does not have dimples Parent cross ______ x ______ Phenotype ratio : Genotype ratio :

  21. Probability • Likelihood of an event occurring • Shown by Punnett Square • Shows how often a gene pairing may occur. **Need large numbers to get accurate predictions** Coin Toss Lab: Flip one coin 10x. Keep track of the # of Heads and Tails you get. 50:50 chance of getting heads or tail if you toss one coin

  22. What happens when you toss two coins? • If you toss 2 coins 100 times, you should get: • 25 Heads/Heads • 50 Heads/Tails • 25 Tails/Tails • Asthe # of trials increases, the ratios predicted by the laws of probability get closer • Actual outcomes get closer to calculated predictions

  23. 5/6

  24. A B C D E

  25. 7/8

  26. A B C D E

  27. 9

  28. A B C D E

  29. A B C D E

  30. 7/8

  31. So you are a right handed person. How do you know if you are pure or a hybrid for the right handed trait? Could you ever have a lefty child? • Test Cross: • Method used to find out if something (or someone) is pure dominant or a hybrid for a given trait. • Cross them with a pure recessive for that trait. If the results come up with a recessive individual, then the parent was a hybrid

  32. Is your black guinea pig pure for its coat color? In Guinea pigs: B = Black coat b = white coat Cross the (BB) guinea pig with a pure recessive (bb) Cross the (Bb) guinea pig with a pure recessive (bb) If:   BB x bb If: Bb x bb If any of the offspring are white coated, then we knew the black guinea pig was BB

  33. Monohybrid crosses: • Cross two hybrids. Bb x Bb Tt x Tt Rr x Rr • Always get a 3:1 phenotypic ratio!!!

  34. Genetic Corn lab • Cover page must be present with a COLOR graphic and the names of all the people in the group along with the date. • Formal Lab write-up so typed & in a specific order

  35. Purpose: What are we trying to determine from our corn plants? • The purpose of this experiment with genetic corn seeds is to determine the Phenotype and Genotype of the parent corn plants from observations of the offspring • Procedure: Explain clearly what we did to set up the lab and how we take care of the plants and collect our data • Data Tables: 2 tables, one for your group only and the other one for the class data • Calculations/Analysis: Determine the F1 Phenotype ratios for your group and the entire class or 2 classes together. Show all your work and calculations. • Questions: You will answer the 10 questions thoroughly and in complete sentences with the question incorporated into the answer

  36. Calculations for Genetic Corn Lab Calculations: Determine the F1Phenotype ratios of your data and the class data. To determine this, divide the # of each color plant by the # of albino plants If you obtained 7 green and 5 white: 7:5 or 1.4:1

  37. Analysis Questions Questions: You are to answer these questions thoroughly and in complete sentences • Could you tell before the seeds germinated which would have the green pigment and which would be albino? Explain • What are the three requirements for seeds to germinate? • Which plants after 1 week were larger? • Why do you think the above was so? • Why do the seeds with albino traits die before the green plants? • Use the results shown in your data tables and your calculations to determine the genotypes andphenotypes of the parents. These are not ratios!! • Show the genetic cross of the parents using a Punnett Square with a key to your two alleles for pigmentation • Using the Punnett Square from question #7, determine the F1genotypic ratio and phenotypic ratio and percentages. • If we wanted more accurate results, what could be done to bring the results closer to the expected phenotype ratios? • Why couldn’t one of the parents be pure recessive for chlorophyll production?

  38. What are your chances of having a blue eyed, blond haired child if one of your parents is brown haired and eyed and the other is a blond with blue eyes?

  39. 4. Law of Independent Assortment • Different pairs of alleles are passed to offspring independent of each other. B = Brown b = White S = Short tail s = Long tail

  40. Dihybrid crosses • Crossing two hybrids, that are hybrid for two different traits • T = Tall stem Y = Yellow seed • t = short stem y = green seed • TtYy x TtYy • Dihybrid cross • Phenotype ratio for a dihybrid is always: • 9:3:3:1 = (3:1)(3:1) 9 – TallYellow 3 – Tallgreen 3 – Short yellow 1 – Shortgreen • Trihybrid would be: 27:9:9:3:9:3:3:1 (3:1)(3:1)(3:1)

  41. F1: TtYy x TtYy Foil each parent to get gamete combinations TY Ty tY ty TY Ty tY ty ____ = Tall Yellow ____ = Tall green ____ = short Yellow ____ = short green

  42. 1. A normal toed, hybrid, dark haired person mates with a hybrid for webbed toes and has light hair. What could be the phenotypes of their children? Parent Cross _________x _______ _____ = Webbed toes _____ = Normal toes _____ = Dark hair _____ = Light hair

  43. 2. Cross an individual who is heterozygous for both curly hair and freckles with a homozygous curly haired, non-freckled person. What will be the possible phenotypes of this cross. Parent Cross _________x _______ _____ = Curly hair _____ = Straight hair _____ = Freckles _____ = No freckles

  44. In fruit flies, red eyes are dominant to sepia eyes and having normal wings is dominant to vestigial wings. Cross a dihybrids for eye and wings____ = Red eyes ___ = Normal wings____ = Sepia eyes ___ = Vestigial wings

  45. 4. Law of Independent Assortment • Different pairs of alleles are passed to offspring independent of each other. B = Brown b = White S = Short tail s = Long tail

  46. F1 Cross: Cross 2 plants from the F1 generation RrYyx RrYy Now FOIL RrYyto figure out the possible gametes for each parent plant RrYy RY Ry rY ry

  47. Phenotype ratio = 100% Round/Yellow Genotype ratio = 100% RrYy

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