Working Genetics Problems

1. Working Genetics Problems Working Genetics Problems writing a key

2. When a trait has two forms and one trait is expressed over the other, the trait that shows up is dominant. The trait that is hidden or masked is recessive. In humans, the gene for brown eye color is dominant over the gene for blue eyes.

3. Dominant traits are represented by upper case letters. B - brown Recessive traits are represented by the same letters as dominant traits but lower case. b - blue

4. You must work genetics problems the same way you work math problems: • Read and reread the problem • Sort and prioritize the information • Eliminate unnecessary information

5. Begin by writing the key. Information needed to write the key will either be stated in the problem or given.

6. Read the problem and write the key. In garden peas, tall plants are dominant over short. Use the first letter, upper case, of the dominant gene to start the key. ‘Big’ T is tall; ‘little’ t is short. T - tall t - short Use the same letter, lower case, for the recessive gene.

7. Read the problem and write the key. In garden peas for seed shape trait, round is dominant to wrinkled. round round wrinkled. wrinkled. Eliminate any unnecessary information. ‘Big’ R is round; ‘little’ r is wrinkled. What is dominant? What is recessive? R - round r - wrinkled

8. Avoid these common mistakes when writing your key. seed shape trait, seed shape trait, In garden peas for the seed shape trait, round is dominant to wrinkled. Do not use the trait. S - round s - wrinkled Do not use the letter of the recessive trait. R - round w - wrinkled

9. Let’s practice. Write the key on your own paper. In rabbits, white coat color is dominant to black. In mice, black coat color is dominant over tan and short tails are dominant over long. In roses, red flower color is dominant over white.

10. Working Genetics Problems Working Genetics Problems writing genotypes

11. Genotype refers to the internal genetic code or blueprint of an organism. The entire genotype of an organism is not always visible or expressed.

12. You must work genetics problems the same way you work math problems: • Read and reread the problem • Sort and prioritize the information • Eliminate unnecessary information

13. Write the key. Information needed to write the key will either be stated in the problem or given. 1 2 Determine the genotypes of both parents. 3 Solve the problem using a Punnett square(later . . .).

14. To determine the genotype of a parent, read the problem carefully. You will NOT be able to write genotypes if you do not understand these terms: dominant recessive pure hybrid heterozygous homozygous Click on each term anytime during this presentation for a definition.

15. Phenotype refers to the physical features or characteristic.

16. Pp How are these flowers different? PP PP PP PP Pp Pp Pp Both flowers have the same physical appearance or phenotype: they are both purple. The flowers have different genetic makeup or genotype.

17. Describe the phenotype of these peas.

18. Pp The genotype is different: one flower is PP, one is Pp. A purple flower can be pure (homozygous dominant) PP or hybrid (heterozygous). The phenotype is the same: both flowers are purple.

19. A white flower can be only be pure (homozygous recessive). pp Why?

20. In garden peas, tall plants are dominant to short. Cross a pure tall pea plant with a short pea plant. Cross Cross pure tall pure tall short short 1 Key T - tall t - short 2 What are the genotypes of each parent plant? tt pure tall short X TT Which genotype is pure tall? Which genotype is short? Tt, TT or tt?

21. In garden peas for pea pod trait, inflated pods are dominant to constricted. Mendel crossed one pea that was heterozygous for the trait with a plant with constricted pods. Write the key and parent genotypes. Write the key and parent genotypes. I - inflated i - constricted heterozygous inflated pods constricted pods X Ii ii X

22. Practice

23. Let’s practice. Write the key and genotypes on your own paper. In guinea pigs, short hair is dominant to long. Cross a homozygous short hair guinea pig with a long hair guinea pig. In corn plants, tall is dominant over short. Cross a corn plant heterozygous for tall with one homozygous for short. In flies, the gene for long wings is dominant over short wing. Cross a hybrid fly with a homozygous dominant.

24. Check Your Work

25. Key: S = short (dominant) s = long (recessive) Genotypes of Parents : S S x s s # 1

26. Key: T = Tall (dominant) t = short (recessive) Genotypes of Parents : T t x t t # 2

27. Key: L = Long (dominant) l = short (recessive) Genotypes of Parents : L l x L L # 3

28. Working Genetics Problems Working Genetics Problems solving problems with Punnett squares

29. Always follow these 3 steps when working genetics problems.

30. Write the key. Information needed to write the key will either be stated in the problem or given. 1 2 Determine the genotypes of both parents. 3 Solve the problem using a Punnett square.

31. Each reproductive cell contributes half of the parent’s genes to its offspring. Possible combinations of offspring genes are shown in a Punnett square. Each parent contributes a purple flower gene. Both parents contribute a white flower gene. White flower color is recessive to purple; therefore, the offspring is white. One parent contributes a purple flower gene; one parent contributes a white flower gene. Purple color is dominant over white. One parent contributes a purple flower gene; one parent contributes a white flower gene. Purple color is dominant over white.

32. Each reproductive cell contributes half of its genes to its offspring. Possible combinations of offspring genes are shown in a Punnett square. Yellow seed color is dominant over green.

33. p Pp P - purple p - white p Pp pp Substitute letters for genes. P Purple flower color is dominant over white. P PP

34. P p P Pp PP p Pp pp What are the different genotypes? Homozygous Dominate Homozygous Recessive Heterozygous

35. P p P Pp PP p Pp pp How many are Homozygous Dominate ? 1 out of 4 1/4 25%

36. P p P Pp PP p Pp pp How many are Homozygous Recessive ? 1 out of 4 1/4 25%

37. P p P Pp PP p Pp pp How many are Heterozygous ? 2 out of 4 2/4 50%

38. P p P Pp PP p Pp pp What are the different phenotypes? Purple White

39. P p P Pp PP p Pp pp How many are Purple ? 3 out of 4 3/4 75%

40. P p P Pp PP p Pp pp How many are White ? 1 out of 4 1/4 25%

41. Yy Yy y Y - yellow y - green Yy Yy y Substitute letters for genes. Y Y Yellow seed color is dominant over green.

42. Y Y Yy Yy y Yy Yy y What are the different genotypes? Heterozygous

43. Y Y Yy Yy y Yy Yy y How many are Heterozygous ? 4 out of 4 4/4 100%

44. Y Y Yy Yy y Yy Yy y What are the different phenotypes? Yellow

45. Y Y Yy Yy y Yy Yy y How many are Yellow ? 4 out of 4 4/4 100%

46. p = white Cross a pure purple flower with a white flower. PP x pp Follow these steps for every genetics problem. 1. Write the key. 1 upper case = dominant trait P = purple lower case = recessive trait 2. Determine both genotypes (parents). 2 Work the problem with Punnett square. Include Genotypes and Phenotypes of offspring with %. 3

47. Practice

48. Let’s practice. Write the key and genotypes on your own paper. Complete the Punnett Square. List genotypes and Phenotypes of offspring. In watermelons, the gene for solid color seeds is dominant over the gene for striped color seeds. Cross a hybrid watermelon with another hybrid. In summer squash, white fruit color is dominant over yellow. Cross a squash plant heterozygous for white with one homozygous for yellow. In rabbits, white coat color is dominant to black. Cross a homozygous white rabbit with a black rabbit.

49. Check Your Work

50. Key: W = white (dominant) w = black (recessive) Genotypes of Parents : W W x w w W W W W W W w w w w w w Genotypes of offspring: 100% Heterozygous Phenotypes of offspring: 100% White