Chromosomes and Inheritance Worksheet
Name ______________________
Date ____________ Period _____
Refer to Section 12-1 for the following.
1. What scientist is famous for his breeding experiments with Drosophila (fruit flies)?
2. What observations did he make that led him to hypothesize that there was a pair of chromosomes that
were sex chromosomes?
3. Males can produce gametes with 2 possible types of sex chromosomes whereas all of a female’s
gametes will have only 1 possible sex chromosome. Explain.
4. Explain why there is a 50% chance of a female and a 50% chance of a male, each time a husband and
wife have a child.
5. a) Which type of sex chromosome can carry more genes?
b) Define “sex linkage”.
6. When Morgan crossed a white-eyed male with a red-eyed female, did the F1 and F2 generation results
agree with predictions based on “Mendelian” inheritance? Explain.
7. Draw a Punnett square to help you explain why only males were white-eyed in the F2 generation.
8. Colorblindness in humans is a recessive X-linked trait. Would you expect more males or females to
be colorblind? Explain.
9. a) What is a “linkage group”?
b) Why do linkage groups exist?
10. a) In a typical dihybrid cross involving 2 parents that are heterozygous for both traits (i.e.: a cross
between 2 F1 generation individuals), “Mendelian” inheritance predicts what phenotypic ratio?
b) Did Morgan observe this ratio in his experiments? Explain.
11. Morgan’s results support which of the following?
a. The genes for body color and wing length are on different chromosomes and are inherited
independently.
b. The genes for body color and wing length are on the same chromosome and are inherited
together.
12. Why was it unlikely that the unexpected phenotypes could be due to mutations?
13. a) What event was the cause of the unexpected phenotypes?
b) When does this event take place?
c) True or False? The unexpected genotypes were caused by new genes being created or old genes
being deleted. Explain.
14. Which is more likely?
a. Genes located far apart are more likely to be separated by crossing-over.
b. Genes located close together are more likely to be separated by crossing-over.
15. What information do scientists use to make chromosome maps?
16. How many map units apart are the genes for body color and eye color? (See Figure 12-5)