Chapter 9

2. Chapter 9 Fundamentals of Genetics

3. Genetics • The field of biology devoted to understanding how characteristics are transmitted from parents to offspring • Heredity is the transmission of characteristics from parents to offspring • Genetics, therefore, is the study of heredity • An understanding of fundamental genetics begins with Gregor Johann Mendel

4. Gregor Mendel • The Father of Genetics • Austrian Monk • University of Vienna • 1840’s and 50’s • Garden pea plants called Pisumsativum

5. Mendel’s Work • characteristic vs. trait • characteristic: generalized feature • Mendel observed 7 characteristics in his pea plants: • Plant height, flower position along the stem, pod color, pod appearance, seed texture, seed color, and flower color • Trait: a specific identifier of the characteristic • Each of Mendel’s characteristics had 2 traits • Plant height: tall vs. short • Flower position along stem: axial vs. terminal • Pod color: green vs. yellow • Pod appearance: inflated vs. constricted • Seed texture: smooth vs. wrinkled • Seed color: yellow vs. green • Flower color: purple vs. white

6. Curiosity Breeds Obsession • Mendel noticed that sometimes plants with one trait (tall for example) were crossed with others of the same trait (tall), the offspring were short • This happened with all 7 characteristics • He starts to manipulate pollination of his pea plants • Interrupts self pollination and controls cross pollination

7. Pollination of Pea Plants • Pollination = gametes (sex cells) from the anther [male part] of a flower are transferred to the gametes (eggs) of the stigma [female part] of a flower • Self pollination = sex cells of anther pollinate eggs in the stigma of the same flower (or the same plant) • Cross pollination = sex cells of anther in one flower pollinates eggs of stigma of flower on another plant of the same species

8. Mendel Creates His Parents • By controlled [experimenter guided] cross pollination, Mendel creates 14 pure strains - one for each pea plant trait • pure for a trait = when pollinated, offspring only produce that trait • a strain = a group of plants pure for a trait • The plants in each of the 14 strains he calls the “parental” generation or P1 generation • Now it’s time to have some genetic fun

9. Mendel’s 14 Pure Strains flower color plant height pod color pod app. seed color seed texture flower position

10. Using the pure strains, Mendel cross pollinates trait vs. trait of the same characteristic Tall vs. Short Purple vs. White Green vs. Yellow Yellow vs. Green Axial vs. Terminal Smooth vs. Wrinkled Inflated vs. Constricted Trait X Trait

11. P1 X P1 yields F1F1 = filial generation

12. P1 X P1 F1 • P1 X P1 F1 • Tall X Short all Tall • Axial X Terminal all Axial • Green X Yellow all Green • Inflated X Constricted all Inflated • Yellow X Green all Yellow • Smooth X Wrinkled all Smooth • Purple X White all Purple

13. Self The F1F1 X F1 F2 • F1 X F1 F2 • Tall X Tall 3Tall:1Short • Axial X Axial 3Axial:1Terminal • Yellow X Yellow 3Yellow:1Green • Inflated X Inflated 3Infalted:1Const. • Green X Greeen 3Green:1Yellow • Smooth X Smooth 3Smooth:1Wrinkled • Purple X Purple 3Purple:1White

15. Explain the F2 • Dominant Traits vs. Recessive Traits • Pollen carrying one trait and egg carrying another [gamete from one parent “P1” carries one trait and gamete from the other parent “P1” carries the same or other trait of the same characteristic] • One trait showing dominance over the other when in the pair • One trait completely dominated in P1 cross • In F1 cross the F2’s brought the other trait back • Mendel named the controls of the traits “factors” • Therefore all traits of the F1 generation are dominant • And, the only way recessive traits can be expressed is when they exist as both factors in the pair

16. Alleles • We now call Mendel’s “factors” alleles • Alleles are represented by letters • Capital letter represents the dominant trait • Lower case letter represents the recessive trait • Example: flower color • P = purple • p = white

17. Law of Segregation • Mendel concluded that parents only contribute one “factor” [allele] to the next generation • He said that the pair of alleles are separated during gamete [sex cell] formation • So each sex cell only gets one allele

18. Law of Independent Assortment • Mendel went on to say that factors for different characteristics are not connected [independent of one another] • In other words, when he crossed plants that differed in two different characteristics, there was no influence of one characteristic over the other • The alleles assorted independently of one another during gamete formation

19. Genetic Terminology Sprouts From Mendel • Genotype – genetic makeup • Homozygous – alleles in the pair are the same • Homozygous dominant – both dominant • Homozygous recessive – both recessive • Heterozygous – alleles in the pair are different • Phenotype – physical result of the genotype

20. Punnett, Mendel, Mendel, Punnett • Reginald Punnett • Punnett squares allow us to predict probabilities • Show possible allelic contributions and combinations of parents • Predicts trait to trait ratios in offspring • 2 types of predicted ratios created by punnett square: • 1. genotypic ratio: • 2. phenotypic ratio:

21. Punnett Practice • Monohybrid crosses • Homozygous Dominant X Homozygous recessive • P1 Purple X P1 White • Homozygous Dominant X Heterozygous • P1 Purple X F1 Purple • Homozygous Recessive X Heterozygous • P1 White X F1 Purple • Heterozygous X Heterozygous • F1 Purple X F1 Purple

22. Punnett Practice Results • 1. P P 2. P P p P p p • p p 4. P p P P p p

23. Homo or Hetero? • If your specimen is showing a dominant trait, how might you determine its genotype? • Example: purple flower • Is it PP or Pp? • Run a Test Cross • Fertilize [mate] your specimen with a specimen showing the recessive trait • Example: P? X pp • If then: • If PP X pp: • If Pp X pp:

24. Your First Word Problem • Your sister moves away and gives you her purebred Labrador retriever, a female named Dandelion. Suppose you decide to breed Dandelion and sell puppies to help pay for your college tuition. Then you discover that two of her four brothers and sisters show hip dysplasia, a heritable disorder arising from a number of gene interactions. If Dandelion mates with a male Labrador known to be free of the harmful genes, can you guarantee to a buyer that puppies will not develop the disorder? Explain your answer.

26. Not all of us is Pea Plant? • Inheritance patterns • Complete Dominance – dominant trait shows in pair • Exampe: all of Mendels pea plant characteristics • Codominance – both alleles for a gene are expressed equally • Example: roan coat • Alleles are represented by both letters being capitalized and the second, or “other,” allele being punctuated by the symbol: ‘ • Example: RR’=roan, RR = black, R’R’ = white • Incomplete Dominance – two or more alleles influence the phenotype to create an intermediate • Example: carnations • Use regular alleles: capital and lower case

27. Complete Dominance • An allele for brown eyes B is dominant over that for blue eyes b. A couple of whom one is brown-eyed and the other blue-eyed have eight children, all brown eyed. What would likely be the genetic make up of each parent in this regard? • A blue-eyed man, both of whose parents were brown-eyed, marries a woman. They have one child who is blue-eyed. What are the genotypes of all the individuals mentioned? • A brown-eyed man whose father was brown-eyed and whose mother was blue-eyed married a blue-eyed woman whose father and mother were both brown-eyed. The couple has a blue-eyed son. For which of the individuals mentioned can you be sure of eh genotype? What are the genotypes? What genotypes are possible for the others?

28. Codominance • Pooh had a colony of tiggers whose stripes went across the body. His American pen-pal, Yogi, sent him a tigger whose stripes ran lengthwise. When Pooh crossed it with one of his own animals, he obtained plaid tiggers.. Interbreeding among the plaid tiggers produced litters of a majority of plaid members, but some crosswise and lengthwise striped animals were also produced. Diagram the crosses made by Pooh, showing the genotypes of the tiggers that account for the coat patterns observed. • In cattle, the gene for straight coat (S) is dominant to its allele for curly coat (s). The gene pairs for red (RR) or white (R’R’) coat color show codominance; Heterozygotes have a roan coat (RR’) (red lightened by intermixed white hairs). • A. If a curly red cow is mated to a homozygous straight white bull, what will the genotype and phenotype of the calf be? • If the calf is mated to a roan animal with curly hair, what are the possible offspring phenotypes?

29. Incomplete Dominance • A hybrid pink snapdragon was crossed with a pure white one. Red flower color is incompletely dominant. Make a diagram to show: • The gene constitution of the parents • Genotypic and phenotypic ratios of the F1 generation

30. Dihybrid Crosses • Combine two characteristics for each individual in the cross • Example: flower color and plant height • Heterozygous, heterozygous X homo dom., hetero • Punnett square has 16 boxes • Must find every possible allelic combination • Use “foil” = “first, outside, inside, last”

32. Foil the Alleles • Example: PpTt X PPTt • For individual 1: • “F”irst = PpTt = PT • “O”utside = PpTt = Pt • “I”nside = PpTt = pT • “L”ast = PpTt = pt • Individual 2: • First = PT; Outside = Pt; Inside = PT; Last = Pt • So the Punnett would begin like this:

33. PpTt X PPTt PT Pt pT pt PT Pt PT Pt

35. Dihybrid Problems • In cats, the allele for black fur (B) is dominant to the allele for brown (b) and the allele for short hair (S) is dominant to the allele for long hair (s). Make a Punnett square for each of the following crosses: • BbSs X Bbss • BBSs X Bbss • What proportion of the offspring from the cross shown in #2 would be expected to be black with short hair? • In tomato plants, the gene for purple stems (A) is dominant to its allele for green stems (a) and the gene for red fruit (R) is dominant to its allele for yellow fruit (r). If two tomato plants heterozytgous for both traits are crossed, state what proprotion fo the offspring are expected to have: • Purple stems and yellow fruits • Green stems and red fruits • Purple stems and red fruits • If 640 seeds resulting this cross are collected and planted, determine how many are expected to grow into plants with: • Red fruit • Green stems • Both green stems and yellow fruit

36. Homework A farmer has three groups of cows: white ones in the clover patch, red ones in the alfalfa field, and roan in the cornfield. He has a roan bull, Ferdinand, who services the cows in all three fields. • A. What color claves should he expect in each field, and in what proportion? • B. Ferdinand dies from a bee sting and the farmer decides to make his herd of cows exclusively roan coat in memory of his beloved bull. He sells all the red and white cows, and vows to sell any red or white calves born later. What color bull should he buy to replace Ferdinand, if he wants to sell as many calves as possible?