Monohybrid and Dihybrid

1. Monohybrid and Dihybrid Honors Biology-Ms. Kim

2. What is a genotype? • A. Brown Hair • B. Homozygous Dominant • C. AATTGGC • D. All of the above

3. Homozygous Dominant • A. aa • B. Aa • C. AA • D. Blue Eyes

4. If I crossed a 2 True Breeding Plants with different traits, their offspring would be… • A. All Heterozygous • B. Hybrids • C. AA, Aa, aa • D. Both A and B

5. What is a carrier? • The heterozygous genotype that does not express the phenotype when disorders are caused by recessive alleles

6. What is the probability that 2 carriers for Cystic Fibrosis will have a child with Cystic Fibrosis/ • 100% • 75% • 50% • 25%

7. What is Probability? • The chance that a specific event will occur • Probability = number of ways a specific event can occur number of total possible outcomes

8. How is Probability used in Genetics? Used to explain the chance of an offspring inheriting a specific trait Each box represents ¼ or 25 %

9. What is a Punnett Square? Way to predict ALL possible outcomes of a cross

10. How do you read a Punnett square? Axes represent possible gametes from each parent Boxes represent possible genotypes for offspring

11. Genetics Vocab (pt 2) • Monohybrid cross cross where parents differ in only one trait (Rr x rr) • Dihybrid cross cross where parents differ in two traits (RrHh x rrHH) • Punnett square – a diagram that shows the gene combinations that mightresult from a genetic cross of two parents

12. Monohybrid Cross • a cross between 2 individuals that looks at 1 trait • Ex: Just looking at the possibility of getting freckles • a cross between 2 individuals that looks at the possibilities of inheriting 2 DIFFERENT traits at one time • Ex: looking at the possibility of getting freckles AND dimples in the SAME offspring Dihybrid Cross

13. Monohybrid Punnett Square Mom’s genotype (Hh)xDad’s genotype (hh) Tall Short Mom’s allele #1 Mom’s allele #2 Hh Dad’s Allele #1 h Dad’s Allele #2 h

14. Genotype Outcome (Ratio) vs. Phenotype Outcome (Ratio) • Genotype Possibilities = the GENOTYPE probabilities (expected results) of offspring • Ex: 50% Hhand 50%hh (0:2:2) • PhenotypePossibilities= the PHENOTYPE probabilities (expected results) of offspring • Ex: 50% Tall50% Short (2:2)

15. Genetics Vocab (pt 3) • Dominant – allele that appears more frequently. It masks the recessive. • Represented by a capitol letter (R=red) • Recessive – allele that appears less frequently (b/c it is repressed when paired with a dominant allele) • Represented by a lower case letter (r=white) • Genotype – a description of the genetic make-up of an individual (TT, Rr) • Phenotype – a description of what an individual LOOKS like (tall, red)

16. Genetics Vocab (pt 4) • Homozygous– two identical alleles for a trait • AA– HOMOZYGOUS dominant • aa– homozygous recessive • Heterozygous – two different alleles for a trait • Aa– HETEROZYGOUS one of each allele

17. Solving Punnett Squares H Biology

18. Punnett squaresStep 1 STEP 1  Define the alleles If a homozygousround pea plant is crossed with a heterozygousround pea plant, what will their offspring look like? Why are we using the same letter? Why not use “R” for round and “W” for wrinkled? R = round r = wrinkled

19. Step 2 If a homozygousround pea plant is crossed with a heterozygousround pea plant, what will their offspring look like? RR x Rr Define the parents

20. Step 3Draw the Punnett square R R R r

21. Step 4 Cross the parents tofind the probability of offspring 1. Bring the top letter down and the side letter over… R R R r

22. Step 5 Find the genotypeand phenotypeof the offspring Genotype: genetic make-up (letters) R R R Phenotype: physical characteristics r

23. Finished Product Key: R=round r=wrinkled Genotype: genetic make-up (letters) R R 2 RR: 2Rr 50% RR 50% Rr R Phenotype: physical characteristics r 4 (round): 100% Round

24. Practice #2 Key: Cross: R = round r = wrinkled RR x Rr Genotype: Phenotype: In pea plants, round seeds are dominant over wrinkled. A plant that is homozygous dominant for round seeds is crossed with a heterozygous plant.

25. Example:Heterozygous x Heterozygous Do the following cross: Mom’s genotype (Hh)xDad’s genotype (Hh) Tall Tall Draw a Punnett Square and determine the offspring’s genotype and phenotype. Give the ratios for each

26. Example:Heterozygous x Heterozygous Mom’s genotype (Hh)xDad’s genotype (Hh) Tall Tall Hh H h Genotyperatio = 25% HH, 50% Hh, 25% hh (1:2:1) Phenotyperatio = 75% Tall, 25% short (3:1)

27. Working Backwards…The Testcross • Allows us to determine the genotype of an organism with the dominant phenotype, but unknown genotype • Genotype is not obvious…could be HH or Hh • Cross an individual with the dominant phenotype with individual that is recessive for the same trait

28. Conduct a test cross, where the unknown dominant individual is crossed with the known recessive . • H _ ?_ x hh

29. Test Cross Mom’s genotype (H?)xDad’s genotype (hh) Tall Short H ? H h If all the offspring are ALWAYS tall…Mom has to be HH If some offspring are short…Mom has to be Hh

30. DIHYBRID CROSSES: Assuming genes follow Mendelian Genetics (complete dominance)

31. Dihybrid Crosses • crosses involving crossing 2 DIFFERENT traits at one time • Example: Mate 2 parents and look at the probability of seeing 2 traits, such as: • eye color AND hair color • freckles AND dimples

32. How do You Do Dihybrid Crosses? • Setting up a complex Punnett Square OR • 2 separate monohybrid • 1 square for EACH trait • use PROBABILITY RULES and MULTIPLY

33. What is a dihybrid cross? • Cross that shows inheritance of two different traits • For example: homozygous round & yellow crossed with a homozygous wrinkled & green seed • RRYY x rryy

34. Setting up a Dihybrid • #1- read the problem & list all 4 alleles • For example: R=round, r=wrinkled, Y=yellow, y=green • #2 – Create the parental genotypes (4 letters each) • Example: RRYY (Round, yellow) x rryy (wrinkled, green) • #3 – Using the “foil” method, determine the sets of gametes (up to 4 possibilities) • Example: 1. RRYY 2. RrYy RY RY, Ry, rY, ry

35. Setting up a Dihybrid RYRyrYry RY RYRyrYryry RY • #4 – Fill in the tops and sides of punnett square with gamete combinations • Example: 1. RRYY 2. RrYy RY RY, Ry, rY, ry • #5 - Genotype and Phenotype as usual

36. Dihybrid Final Product RYRyrYry RY Round and Yellow Round and Yellow Round and Yellow Round and Yellow R=round, r=wrinkled, Y=yellow, y=green RRYY = RRYy = RrYY = RrYy = So…we can say that all of our offspring (100%) will be round and yellow!

37. Dihybrid Example Problem #1 RRYy x rrYy rY, ry RY, Ry Round is dominant over wrinkled Yellow is dominant over green Two pea plants produce offspring. One is round and heterozygous for yellow seed color. The other is wrinkled and heterozygous for yellow seed color. STEP 1: Parental genotypes = Possible gametes

38. Dihybrid Example Problem #1 RY Ry rY ry STEP 2: Set up the dihybrid cross using the gametes from before…

39. Dihybrid Example Problem #1 RY Ry rY ry 3 Round, yellow 1 Round, green STEP 3: Determine the genotype and phenotype! RY Ry Genotype: Phenotype: 1 RrYY: 2 RrYy : 1 Rryy

40. Dihybrid Example Problem #2 • Black fur is dominant to white fur • Long hair is dominant to short hair • Two guinea pigs mate. The dad is homozygous for black fur and long hair. The mom is also homozygous, but for white fur and short hair. • 1) Determine the dominant & recessive traits • 2) Determine the possible gametes of each parent • 3) What is the only gamete possibility for their offspring?

41. Dihybrid Example Problem #2 1) Key: Black fur is dominant (B) to white fur (b) Long hair is dominant (L) to short hair (l) Two guinea pigs mate. The dad is homozygous for black fur and long hair. The mom is also homozygous, but for white fur and short hair. 2) Determine the possible gametes of each Dad  ALL BL Mom  ALL bl 3) What is the only gamete possibility for their offspring? GENOTYPE: 100% BbLl PHENOTYPE: Black, long-haired

42. GgbbxggBb G= Grey hair g = white hair B = Black eyes b = red eyes • FOIL (FIRST, OUTER, INNER, LAST) Ggbb X ggBb GbgB Gbgb gbgB gbgb

43. GgbbxggBb Gb gb gB gb

44. GgbbxggBb GbgbGbgb gB gb gB gb

45. GGbb x ggBb • GENOTYPE POSSIBILITIES: GgBb = 4/16 or ¼ = 25% Ggbb= 4/16 or ¼ = 25% ggBb= 4/16 or ¼ = 25% ggbb= 4/16 or ¼ = 25% • Genotypic ratio: 1GgBb: 1 Ggbb: ggBb : 1 ggbb • PHENOTYPE POSSIBILITES: Grey Hair Black Eyes: 25% Grey Hair Red Eyes: 25% White Hair Black Eyes: 25% White Hair Red Eyes: 25% • Phenotypic ratio: 1: 1: 1: 1

46. Practice • In pea plants, yellow seeds are dominant to green seeds in peas. Round seeds are dominant over wrinkled. Cross two plants that are heterozygous for both traits. • Write the genotypes for the parents. • Then use “FOIL” to determine your possible allele combinations from each parent • Then set up Punnett Square and fill in the boxes • Then figure out the genotypic and phenotypic ratios

47. YyRr x YyRr YR Yr yR yr YR Yr yR yr

48. YyRr x YyRr YR Yr yR yr YR Yr yR yr

49. YyRr x YrRr GENOTYPE POSSIBILITIES: YyRr= 4/16 or 1/4 = 25% YYRr=2/16 or 1/8 =12.5% YyRR=2/16 or 1/8 =12.5% Yyrr=2/16 or 1/8 =12.5% yyRr=2/16 or 1/8 =12.5% YYrr= 1/16 = 6.25% YYRR= 1/16 = 6.25% yyRR=1/16 = 6.25% yyrr=1/16 = 6.25% PHENOTYPE POSSIBILITES: 9 yellow, round 3 yellow, wrinkled 3 green, round 1 green, wrinled

50. Would you like to know a few SHORT CUTS?