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Chapter 9

Chapter 9. Fundamentals of Genetics. Why do you have your “father’s” eyes or your “mother’s” hair color?. Genetics – field of biology dealing with how characteristics are transmitted from one generation to the next Heredity – transmission of characteristics from parent to offspring.

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Chapter 9

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  1. Chapter 9 Fundamentals of Genetics

  2. Why do you have your “father’s” eyes or your “mother’s” hair color? • Genetics – field of biology dealing with how characteristics are transmitted from one generation to the next • Heredity – transmission of characteristics from parent to offspring

  3. Gregor Mendel • Austrian monk - 1866 – Father of Genetics • Worked with garden pea, Pisum sativum • Studied statistics • Observed 7 pea characteristics • White or purple flowers • Axial or terminal flower position • Long (tall) or short stems • Round or wrinkled seeds • Yellow or green seeds • Inflated or constricted pods • Yellow or green pods

  4. Mendel’s work • Controlled the process of pollination – pollen grains from the anther of the stamen land on the stigma of the pistil (female repro organ) • Peas self-pollinate – transfer of pollen to stigma of the same flower • Instead, Mendel cross-pollinated them – Taking pollen from one plant to pollinate the stigma of another flower

  5. Removed the stamen (male reproductive part) to prevent self-pollination • Used the stamen from a tall plant and pollinated only flowers from other tall plants • Observed generations for 2 years to be certain of purebreds • Tall x Tall Short x Short • Crossed plants with contrasting traits • Tall x Short Short x Tall

  6. P = Parental generation • F1 = 1st Filial generation (Offspring) • F2 = 2nd Filial generation (next set of offspring from an F1 generation cross)

  7. P1: Pure Tall x Pure Short T = Tall • TT tt t = Short • F1: Tall Tt • P2: F1 Tall X F1 Tall • Tt Tt • F2: 3 Tall 1 Short • The “lost” trait reappears! • TT Tt Tt tt Only one trait showed

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

  9. So what did he conclude? • Concept of Unit Characters: The inheritance of each trait is determined by “units” or “factors” that are passed on. - We know these as “genes” - These units occur in pairs. One from each parent

  10. 2. Law of Dominance: One factor “masks” the appearance of another factor and 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 and a recessive trait (Tt) • Allele – The alternate genes for a given trait (Tall or short) – genes occur in pairs

  11. Law of Segregation: - Paired factors separate during meiosis. - - - Each gamete receives only 1 factor of each pair. - A pair of factors is separated during the formation of the gametes. • Law of Independent Assortment: - Different pairs of alleles are passed to offspring independent of each other as long as the factors are not located on the same chromosome. - You inherited your eye color independently from your hair color.

  12. Let’s get Crossing now! 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 Phenotype – Tells appearance (describes the trait) Tall (if TT or Tt) Short (if tt) NO HYBRIDS HERE! Homozygous– Pure for the trait (TT or tt) Heterozygous – Hybrid or mixed for a trait (Tt)

  13. Probability • The likelihood of a specific event occurring. • Expressed as a decimal, fraction, percentage or a ratio. • Probability = number of times an event is expected to happen Number of opportunities for an event to happen What is the likelihood of being left handled in our class? Probability = # of left handed students X 100 Total number of students in classroom

  14. What is the probability of pulling out an Ace from a deck of cards? • Probability = 4 (# of Aces in a deck) x 100 52 (# of cards in a deck) 1:13 or 7.6% of the time • What is the probability of getting heads or tails from a coin flip? • Probability = 1:1 50%

  15. Punnett Squares Shows possible gene pairing and probability of each pairing There are two kinds of sperm &/or 2 kinds of eggs depending on the genes that they carry. Genes of 1 parent Phenotype ratio: 100% Tall Genotype ratio: 100% Tt (Hybrid) Genes of 1 parent

  16. Possible crosses 1. Do the Punnett squares & determine the: • Phenotype ratios • Genotype ratios Trait: Purple flower is dominant to white flower P = Purple flower p = white flower 1. PP x PP 2. PP x Pp 3. PP x pp 4. Pp x Pp 5. Pp x pp 6. pp x pp

  17. If you are right handed, how do you know if you are homozygous right handed or hybrid? Test Cross: Method used to find out if something (someone) is pure dominant or 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

  18. In Guinea pigs: B = Black coat b = White coat • Cross a BB guinea pig with a pure recessive (bb) • Cross a Bb guinea pig with a pure recessive (bb) Bb x bb BB x bb

  19. How are two traits, not linked on the same chromosome inherited (according to the Law of Independent Assortment) inherited? • Dihybrid crosses: • A cross between individuals that involve two pairs of contrasting traits. • This is where your FOILing talents come in! • Foil this! AaBb

  20. In pea plants Round seeds are dominant over wrinkled seeds and Yellow seed coats are dominant over green seed coats R = Round Y = Yellow r = wrinkled y = green P1:Cross two pea plants, homozygous for contrasting traits, what will result? RRYY x rryy

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

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

  23. 9:3:3:1 Phenotype ratio: Round/Yellow = 9/16 Round/Green = 3/16 Wrinkled/ Yellow = 3/16 Wrinkled/Green = 1/16

  24. Always a 9:3:3:1 ratio when you cross 2 dihybrids!! 3:1 ratio with a monohybrid cross!!!

  25. Is it always so black and white? What happens when you cross someone with blue eyes and brown eyes? Do you always get brown eyes? Incomplete dominance • Two or more alleles influence the phenotype, resulting in an intermediate phenotype. • Traits are blended When you cross a red and a white 4:00 flower, you get pink 4:00’s

  26. Do the Punnett square now to figure out the phenotype and genotype ratios R = Red r = white P1: Red x white F1 Cross: Pink x Pink Genotype ratio: Phenotype ratio:

  27. A round face crossed with a square face results in an oval shaped face. • Show the cross which would result in an oval shaped face. 2. Cross two individuals who both have oval shaped faces

  28. Codominance Occurs when both alleles for a gene are expressed in a heterozygous offspring. Roans

  29. R = Red R’ = White or R = Red W = White B = Black B’= White Phenotype ratio = 100% Roan Genotype ratio = 100% RR’

  30. In Humans, Blood types and Sickle cell Anemia exhibit codominance 1. Blood Types: Exhibit Dominance, Codominance and Multiple Alleles Allele for A proteins on RBC = Allele for B proteins on RBC. (Codominance) Alleles for A and B protein are Dominant to O There are three alleles to determine blood type A, B and O (Multiple alleles)

  31. A = B > o or IA = IB > i

  32. Sickle Cell Anemia – Due to a gene mutation, normal red blood cells are not formed, instead, sickled shaped cells are produced HNHN = All Normal RBC HNHS = Carrier for SCA – ½ the RBC are sickle shaped. Show some of the symptoms of SCA HSHS = SCA – All RBC will be sickle shaped.

  33. Distribution of Malaria Distribution of SCA

  34. Advantage to being a Carrier • People who are carriers for SCA, have a partial resistance to Malaria. • People who are homozygous for SCA have a total resistance to Malaria though they usually die in childhood. • 100,000/year • 1.5 million/year die from Malaria

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