AP Biology - Quia



RG 8 – Inheritance, Genes, and Chromosomes*

*Adapted and modified from Robbyn Tuinstra’s work

For additional help, try the website . Here you will find an excellent series of tutorials for Chapters 10-18 of our book. Explore panels 1-11 to guide you through this chapter. Be sure to click on the animation and problem links to get the complete info.

Section 8.1 – Mendelian Laws of Inheritance

1. Describe Mendel’s classic (monohybrid) pea plant experiment. Include what Mendel to obtain the P, F1, and F2 generations.

2. State the Law of Segregation. Explain how Mendel arrived at this law experimentally.

3. Define and give an example of each of the following.

|Gene locus | |

|Homozygous | |

|Heterozygous | |

|Genotype | |

|Phenotype | |

|Allele | |

|Dominant allele | |

|Recessive allele | |

4. In a monohybrid cross, how do the events of meiosis explain Mendel’s first law? In a dihybrid cross, how does meiosis explain Mendel’s second law?

5. When we predict the expected genotype of an offspring, why do we consider the alleles they inherit as two separate, independent events? What probability law applies?

6. When predicting phenotype, what probability law applies?

7. Demonstrate that the expected phenotype and genotype probabilities of offspring from two heterozygous parents are the same whether you use the two probability laws above or a Punnett square.

8. What does it mean when we say “Chance has no memory”?

9. How did Mendel use a testcross to test the law of segregation?

REVIEW PROBLEMS - Laws of Probability

10. State the Rule of Multiplication.

a. You have 2 coins. What is the probability that you will flip two heads?

b. What is the probability that offspring of an F1 generation cross will be homozygous recessive?

11. State the Rule of Addition.

7. You have 2 coins. What is the probability that you will flip a heads and a tails?

8. What is the probability that two heterozygous parents will produce heterozygous offspring?

9. What is the probability that two parents heterozygous for both height and flower color will produce tall offspring with purple flowers?

12. For the following crosses, indicate the probability of obtaining the indicated genotype in an offspring. Remember it is easier to treat each gene separately as a monohybrid cross and then combine the probabilities.

|Cross |Offspring |Probability |

|AAbb x AaBb |AAbb | |

|AaBB x AaBb |aaBB | |

|AABbcc x aabbCC |AaBbCc | |

|AaBbCc x AaBbcc |aabbcc | |

Mendel’s Law of Independent Assortment

13. What is a dihybrid cross?

14. State the Law of Independent Assortment. Explain how Mendel arrived at this law.

Human Genetic Disorders and Pedigree Analysis

15. Genetic counselors construct genetic pedigrees. What information can they obtain?

16. How can a pedigree analysis distinguish between an autosomal dominant pattern of inheritance from an autosomal recessive pattern of inheritance?

Section 8.2 – Alleles and Genes Interact to Produce Phenotypes

17. Explain why phenotypes do not always follow the simple patterns of Mendelian inheritance.

18. Define a mutation.

19. Describe of how each of the following inheritance patterns deviate from expected 3:1 ratio of a heterozygous cross and give an example of each in humans.

|Inheritance Pattern |Deviation from 3:1 ratio |Example |

| | | |

|Incomplete Dominance | | |

| | | |

| | | |

|Multiple | | |

|Alleles | | |

| | | |

|Codominance | | |

| | | |

|Polygenic Inheritance | | |

| | | |

20. A rooster with blue (actually gray) feathers is mated with a hen of the same phenotype. Among their offspring, 15 chicks are blue, 6 are black, and 8 are white.

a. What is the simplest explanation for the inheritance of these colors in chickens?

b. What offspring would you predict from the mating of a blue rooster and a black hen?

21. Explain why a type O person can donate blood to all other blood types (a universal donor) but can only receive type O blood.

22. Blood typing has often been used as evidence in paternity cases. For the following mother and child combination, indicate which blood groups of potential fathers would be exonerated.

|Blood Type of Mother |Blood Type of Child |Blood Group that would Exonerate Man |

|AB |A | |

|O |B | |

|A |AB | |

|O |O | |

|B |A | |

23. Color pattern in a species of duck is determined by a pair of genes with three alleles. Alleles H and I are codominant, and allele i is recessive to both. How many phenotypes are possible in a flock of ducks that contains all the possible combinations of these three alleles?

24. What is epistasis? Give an example.

25. In guinea pigs, the gene for production of melanin is epistatic to the gene for the deposition of melanin. The dominant allele M causes melanin to be produced; mm individuals cannot produce the pigment. The dominant allele B causes the deposition of a lot of pigment and produces black guinea pigs, whereas only a small amount of pigment is laid down in bb animals, producing a light-brown color. Without an M allele, no pigment is produced so the allele B has not affect and the guinea pig is white. A homozygous black guinea pig is crossed with a homozygous recessive white: MMBB x mmbb. Give the phenotypes of the F1 and F2 generations.

26. The height of spike weed is a result of polygenic inheritance involving three genes, each of which can contribute 5 cm to the plant. The base height of the weed is 10 cm, and the tallest plant can reach 40 cm.

a. If a tall plant (AABBCC) is crossed with a base-height plant (aabbcc), what is the height of the F1 plants?

b. How many phenotypic classes will there be in the F2? List them.

Section 8.3 – The Chromosomal Theory of Inheritance

27. Explain the crosses conducted by T.H. Morgan in Figure 8.13. Explain how/why the observed phenotypic ratios deviate from those predicted by a simple Mendelian dihybrid cross involving a heterozygous and homozygous recessive parents.

28. Why didn’t all the offspring from this cross exhibit only maternal or paternal traits?

29. What is a recombinant phenotype?

30. Define the following terms.

| | |

|Gene linkage | |

|Linkage group | |

| | |

|Recombinant Frequencies | |

| | |

| | |

31. What is a linkage map? What do the numbers listed in the chromosome mean?

32. What is the equation for recombination (cross-over) frequency?

33. If the genes for two traits are located on separate chromosomes, what would be the possible gametes produced from an AaBb individual?

34. If the following genes are unlinked (on separate chromosomes) what would the expected phenotypic ratio of the cross AaBb x aabb?

35. Calculate the recombination frequency for this cross.

36. If the genes for these traits are located on the same chromosome (linked), what possible gametes could be produced from an AaBb individual?

37. What would be the expected phenotypic ratio of an AaBb x aabb cross if these genes are linked?

38. How many recombinant phenotypes were produced here? What is the recombinant frequency then?

39. Assuming you did the following cross: AaBb x aabb and obtain the following results: 35 dominant in both A and B; 15 dominant for A, recessive for B; 15 dominant for B, recessive for A; 35 recessive for both

a. Identify the recombinant phenotypes here. Then calculate the recombinant frequency.

b. Do you believe the genes for these traits are on the same chromosome or different chromosomes?

c. If you believe they are on the same chromosome, how many map units apart are they?

40. If you did the above cross and got the following results: 25 dominant for both A and B; 25 dominant for A, recessive for B; 25 dominant for B, recessive for A; 25 recessive for both A and B

a. Identify the recombinants here. Calculate the recombination frequency.

b. Do you believe the genes for these traits are on the same chromosome or different chromosomes? Can you even tell? (Hint: Compare this number with the number you got in question 39)

41. What can you say about the upper and lower limits of calculating the recombination frequency?

42. So if two genes are linked, they should reside on the same chromosome and the recombination frequency will range between _______________? But, if two genes are unlinked, are they necessarily on separate chromosomes? Why or Why not?

43. In general, if two genes are linked (on the same chromosome), what is the relationship between the crossing over frequency and the distance between these genes?

44. Why does recombination frequency increase with distance?

45. Go back to meiosis now and be sure you understand how crossing over works and. To test your knowledge, predict the gamete combinations that could be produced from the following diploid cells, and the expected frequency of recombinant gametes given.

Assume genes are 10 map units apart in both parent cells.

Practice Problems – Gene Linkage

1. A wild-type fruit fly (heterozygous for gray body color and normal wings) was mated with a black fruit fly with vestigial wings. The offspring gave the following distribution: wild-type, 778; black-vestigial, 785; black-normal, 158, gray-vestigial, 162.

a. What are the phenotypes of the recombinants?

b. What is the recombination frequency between the genes for body color and wing type?

2. In guinea pigs, black (B) is dominant to brown (b), and solid color (S) is dominant to spotted (s). A heterozygous black, solid-colored pig is mated with a brown, spotted pig. The total offspring for several litters is: 16 black solid, 5 black spotted, 5 brown solid, 14 brown spotted

a. Calculate the recombination frequency for the cross.

b. Are these genes linked or nonlinked?

c. How do you know?

3. The following recombination frequencies were found. Determine the order of these genes on the chromosome.

a—c 10% b—c 4% c—d 20%

a—d 30% b—d 16%

a—e 6% b—e 20%

-----------------------

A

b

a

B

A

B

a

b

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