Name Date

AP: Chapter 15

The Chromosomal Basis of Inheritance

1. Describe some of the pieces of information that scientists discovered that contributed to the “Chromosome Theory of Inheritance”?

2. Summarize the chromosomal Theory of Inheritance.

3. Why was Thomas Hunt Morgan’s choice of the fruit fly a good model organism?

4. Describe Morgan’s first mutant. Why was it so significant from the wild type?

5. Show the cross P, F1, F2 for the white-eyed male mutant.

6. What happens when we trace the inheritance of traits found on the same chromosome?

7. Use the diagram to trace the body color and wing shape in this linked two trait cross. Provide the genotypes, phenotypes, and sexes for each generation.

8. What is recombination and when does it occur?

9. How is recombination frequency calculated?

10. A wild-type fruit fly (heterozygous for gray body color and normal wings) is mated with a black fly with vestigial wings. The offspring have the following phenotypic distribution: Wild type, 778; black-vestigial, 785; black-normal, 158; gray-vestigial, 162. What is the recombination frequency between these genes for body color and wing size.

11. Determine the sequence of genes along a chromosome based on the following recombination frequencies: A-B, 8 map units; A-C, 28 map units; A-D, 25 map units; B-C, 20 map units; B-D 33 map units.

12. What determines the sex in humans?

13. Why are sex-linked recessive traits more common in human males than females?

14. How many X chromosomes are typically expressed in humans and cats?

15. What happens to X chromosomes that are inactivated?

16. How many Barr bodies would be found in a person with: XXY XO XXX

17. Define each term & indicate when each occurs.

a. aneuploidy

b. polyploidy

18. Identify each of the alterations of chromosome structure.

19. List and describe two specific examples of non-disjuction that occurs in humans.

20. Describe genomic imprinting and give an example.

21. An investigator observes the following when red-eye, vestigial-wing Drosophila are mated with sepia-eye, normal-wing flies:

Red-eye, normal-wing 1,130

Red-eye, vestigial wing 371

Sepia-eye, normal wing 379

Sepia-eye, vestigial wing 120

a. Write a hypothesis that describes the mode of inheritance of the trait(s) studied. This is your null hypothesis.

b. Complete the table

Phenotype / # observed (o) / # expected (e) / (o-e) / (o-e)2 / (o-e)2
e
X2=∑(o-e)2 =
e

c. According to the critical value of X2 for .01 probability, can you accept or reject the null hypothesis. Explain why.

Degrees of Freedom (df)
Probability (p) / 1 / 2 / 3 / 4 / 5
0.05 / 3.84 / 5.99 / 7.82 / 9.49 / 11.1
0.01 / 6.64 / 9.21 / 11.3 / 13.2 / 15.1
0.001 / 10.8 / 13.8 / 16.3 / 18.5 / 20.5

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