Probability & Genetics 11-2

1. Probability & Genetics11-2

2. Genetics & Probability • Mendel’s laws: • segregation • independent assortment reflect same laws of probability that apply to tossing coins or rolling dice

3. Probability is the likelihood that a particular event will occur. It does not ALWAYS happen (think Deal or No Deal) Can be written as a decimal, percentage, ratio, or fraction How do we use the principles of probability in our daily lives? Ex. Horse racing NCAA March Madness Superbowl Coin Toss Las Vegas $$$$$ What is Probability?

4. P P P p PP Pp Probability & genetics • Calculating probability of making a specific gamete is just like calculating the probability in flipping a coin • probability of tossing heads? 50% • probability making a gamete… 50% 100%

5. Determining probability • Number of times the event is expected Number of times it could have happened • What is the probability that you picked an odd number when picking from 1-10? There are five odd numbers between 1 and 10. • Or you can express it as a fraction: 5/10. Since it's a fraction, why not reduce it? The probability that you will pick an odd number is 1/2. • Probability can also be expressed as a percent...1/2=50% Or as a decimal...1/2=50%=.5

6. Rule of multiplication • Chance that 2 or more independent events will occur together • probability that 2 coins tossed at the same time will land heads up Or .25 or 25% or 1:4 • probability of Pp x Pp  pp 1/2 x 1/2 = 1/4 1/2 x 1/2 = 1/4

7. Terminology and Directions Punnet Squares

8. ALLELES= (WARNING - THIS WORD CONFUSES PEOPLE; READ SLOW) alternative forms of the same gene.  • Hair Texture Gene- Straight (S) or Curly (s) • One form of the gene codes for curly hair.  • A different code for of the same gene makes hair straight.  • So the gene for hair texture exists as two alleles --- one curly code (s), and one straight code (S).

9. Alleles • Dominant (Capital Letter) • Shows up more in a population, Expresses itself when it is present • Recesive (Small Letter) • Shows up less in a population, only shows when there is no dominant trait.

10. GENOTYPE = the genes present in the DNA of an organism.  • We will use a pair of letters (ex: Tt or YY or ss, etc.) to represent genotypes for one particular trait.  • There are always two letters in the genotype -one letter (gene) from mama organism -one letter (gene) from papa organism

11. Phenotypes • PHENOTYPE = how the trait physically shows-up in the organism.  • Wanna know the simplest way to determine an organism's phenotype ?  • Look at it.  Examples of phenotypes: blue eyes, brown fur, striped fruit, yellow flowers.

12. VOCAB • Now, turns out there are three possible GENOTYPES – • two big letters (like "TT"), • one of each ("Tt"), or • two lowercase letters ("tt"). • Since WE LOVE VOCABULARY, each possible combo has a term for it.

13. Hetero/ Homo • Two capital (TT) or • Two lowercase (tt) in the GENOTYPE • Called HOMOZYGOUS • ("homo" means "the same").  • Sometimes the term "PUREBRED" is used instead of homozygous.

14. Heterozygous • When the GENOTYPE is made up of one capital letter & one lowercase letter (ex: Tt) it's called HETEROZYGOUS ("hetero" means "other").  • Just to confuse you, a heterozygous genotype can also be referred to as HYBRID.

15. Let's Summarize: • Genotype = genes present in an organism (usually abbreviated as two letters) • AA = homozygous = pure • Aa = heterozygous = hybrid • aa = homozygous = pure

16. Quick Review • Genotype= genes of the organism • “Letters” ex. TT or Tt or tt. • Phenotype= the physical appearance of a trait in an organism • What it physically looks like. • The Letters are chosen for the Dominant trait of the allele.

17. Homozygous and Heterozygous • When we have two capital or two lowercase letters in the GENOTYPE (ex: TT or tt) it's called HOMOZYGOUS ("homo" means "the same").  • Sometimes the term "PUREBRED" is used instead of homozygous. • When the GENOTYPE is made up of one capital letter & one lowercase letter (ex: Tt) it's called HETEROZYGOUS("hetero" means "other").  • Just to confuse you, a heterozygous genotype can also be referred to as HYBRID.

18. Dominant and Recessive • Dominant (Capital Letter) • Shows up more in a population, Expresses itself when it is present • Recesive (Small Letter) • Shows up less in a population, only shows when there is no dominant trait.

19. Punnet Square • Help determine the probability of getting a gene, not what you actually get • Basic punnet squares look like window panes or tic tac toe boards. OR

20. Baby steps of Punnet Squares • Determine and write down the genotypes of the parents • Draw a punnet square of appropriate size • Split the letters of the parents and put them on the outside • Do the punnet square • Summarize the results by showing genotypic and phenotypic ratios

21. Punnet Square Practice • Steps 1 -Determine the genotypes of the parents and write them down • Tall (T) is dominant to short pea plants (t). Cross a short pea plant with one that is heterozygous for tallness. What are the parents genotypes? • tt x Tt

22. Cross a short pea plant with one that is heterozygous for tallness. What are the parents genotypes? 3. Draw a p-square 4. Split the letters of the parents and put them on the outside 5. Do the punnet square tt x Tt t t T t Tt Tt tt tt

23. Summarize the results by showing genotypic and phenotypic ratios t t T t Genotypic Ratio (letters) TT- 0 or 0/4 or 0% Tt- 2 or 2/4 or 50% tt- 2 or 2/4 or 50% Phenotypic (looks) Tall- 2 or 2/4 or 50% Short- 2 or 2/4 or 50%

24. Decide what the genotypes of the parents are • In humans, brown eyes, B, are dominant to blue eyes, b. If the father has brown eyes and is homozygous dominant for the trait, BB, and the mother has blue eyes and is homozygous recessive for the trait, bb, what are the possible genotypes and phenotypes of their offspring. • Father-homozygous dominant-BB • Mother-homozygous recessive-bb

25. B B • Then, write the genotype for one parent across the top of the punnett square, and the genotype for the other parent along the left side of the square. b b

26. B B • Fill in the boxes inside with whatever letter are on top and to the left of them b b

27. B B • The genotypes inside the boxes represent the possible gene combination of their offspring • Each box is a 25% or ¼ chance • So, the genotypes of all the offspring in this genetic cross would be Bb • Because there is at least one dominant allele the phenotype (appearance) would also be dominant all offspring would have brown eyes Bb Bb b Bb b Bb

28. Try another punnett square • Two brown eyed parents, who are both heterozygous for the trait, Bb, mate. What are the chances they will have a blue eyed child?

29. Step 1 • What are the genotypes of the 2 parents?

30. Step 3 B b B b

31. Step 4 B b B BB Bb b Bb bb

32. Step 5 • Genotypes of offspring • BB-1/4 or 25% • Bb-1/2 or 50 % • Bb-1/4 or 25% • Phenotypes of offspring • Brown eyes (BB and Bb)-3/4 or 75% • Blue eyes (bb)-1/4 or 25% • Probability of blue eyed child=1/4 or 25 % B b B BB Bb b Bb bb

33. Biology Dihybrid Crosses

34. What is a dihybrid cross? • Work 2 genes at once • Find the expected offspring for both traits • They are a little more work than the monohybrid cross, but… • So much fun!! 

35. Steps to solving a dihybrid problem • 1. Read the problem and find the two separate traits. • Sample problem: • In Springfield, red hair (H) is dominant to blue hair (h) and having four fingers (F) on your hand is dominant to having five fingers (f). If Side Show Bob and Mrs. Van Houten get married and decide to have a little brother for Millhouse, what is the chance that the newborn will have red hair and five fingers if Side Show is heterozygous for red hair and heterozygous for four fingers and Mrs. Van Houten has blue hair and is homozygous for four fingers?

36. Genotypes • 2. Find the two parents and write down their genotypes. • HhFf x hhFF

37. What do they Want? • 3. Read the question and see what you have to look for. Do they want you to find a ratio, percent, fraction, or do they want you to list all possibilities?

38. Math Class • 4. Once you have found all the information, you can start to set up the problem by finding the gametes for each parent by using FOIL. • FOIL stands for First, Outside, Inside, Last

39. FOIL • Here is an example of how to use FOIL: • (a + b) * (c + d) • First = (a + b) * (c + d) = ac • Outside = (a + b) * (c + d) = ad • Inside = (a + b) * (c + d) = bc • Last = (a + b) * (c + d) = bd • So our pairs are: ac, ad, bc, bd

40. Parent Genotypes • Now try it with the parents alleles • Side Show = HhFf • So, HF, Hf, hF, hf • Mrs. Van Houten = hhFF • So, hF, hF, hF, hF

41. DiHybrid (Double Cross) • 5. Once you have the gametes, you have to line them up in a punnett square. • You are going to need a bigger square! • Put the gametes of one parent across the top of the square and the other down the side of the square

42. HF Hf hF hf hF hF hF hF

43. 6. Now you have to do the actual cross. • This is a single box example. • Remember to always put the two like alleles back together, • The same letters go together, and • The capital letter should go first • Keep the same sequence of alleles (letters) HF HhFF hF

44. Fill in the rest of the box!

45. HF Hf hF hf hF hF hF hF

46. Genotypic Ratio • 7. Find the genotypic ratio • HhFF = 4/16 (25%) • HhFf = 4/16 (25%) • hhFF = 4/16 (25%) • hhFf = 4/16 (25%)

47. Phenotypic Ratio • 8. Find the phenotypic ratio • Red hair, four fingers = 8/16 (50%) • Blue hair, four fingers = 8/16 (50%)

48. Answer the Question • 9. Now, don’t forget to answer the question! • If Side Show Bob and Mrs. Van Houten get married and decide to have a little brother for Millhouse,what is the chance that the newborn will have red hair and five fingersif Side Show is heterozygous for red hair and heterozygous for four five fingers and Mrs. Van Houten has blue hair and is homozygous for four fingers? • 0%

49. Other options for Genetics

50. PP = purple Pp = purple pp = white Review: Dominant/Recessive • One allele is dominant over the other (capable of masking the recessive allele)