Name: ___________________________
Period: ________
Linked Genes Practice Problems
AP Biology
Directions: Answer the following questions. Make sure to show your work on genetics
problems (no work, no credit). This assignment will be due Monday, February 8, 2016.
1. In cosmos plants, purple stem (A) is dominant to green stem (a), and short petals (B) is
dominant to long petals (b). AABB plants were crossed with aabb plants to generate F1
dihybrids (AaBb), which were then test crossed. 900 offspring plants were scored for stem
color and flower length.
a. Write the expected phenotypic ratio (make a Punnett Square if needed).
b. Determine the Chi-Square value if the following results were observed.
Testcross
Offspring
A-B-
Expected (e)
Observed (o)
(o-e)
(o-e)2
(o-e)2/e
341
aaB-
356
A-bb
98
aabb
105
Chi Square Value = _____________
c. How many degrees of freedom?
d. What is the p value? Is the data significant?
e. Are the genes for stem color and petal length linked or unlinked?
2. Genes A, B, and C are located on the same chromosome. Testcrosses show that the
recombination frequency between A and B is 28%, between A and C is 12%, between B and
C is 16%. Determine the linear order of the genes and draw a linkage map.
3. In peas, yellow seeds (A) are dominant over green seeds (a). In a cross between two plants
both heterozygous for seed color, the following was observed:
yellow =
4400
green =
1624
a. What do you predict the expected phenotypic ratio to be?
b. State a NULL hypothesis for this experiment.
c. What is the Chi-Square value?
d. How many degrees of freedom?
e. What is the p value? Do you accept or reject your null hypothesis?
4. 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
offspring from several litters are as follows: black solid: 16, black spotted: 5; brown solid: 5;
and brown spotted: 14. Calculate the recombination frequency. Are these genes linked or
unlinked?
5. In a flowering plant, white flowers (B) are dominant over red (b), and short plants (E) are
dominant over tall (e) plants. When a double heterozygote (BbEe) plant was testcrossed, the
resulting phenotypes were observed:
white, short = 195
red, short = 102
white, tall = 113
red, tall = 186
a. What do you predict the expected phenotypic ratio to be?
b. State a NULL hypothesis for this experiment.
c. What is the Chi-Square value?
d. How many degrees of freedom?
e. What is the p value? Are the genes linked or unlinked?
6. A homologous dominant tomato plant with red fruit and yellow flowers was crossed with a
homologous recessive tomato plant with golden fruit and white flowers. The F1 all had red
fruit and yellow flowers. The following phenotypes were obtained in the F2:
a. Red fruit and yellow flowers: 41
b. Red fruit and white flowers: 7
c. Golden fruit and yellow flowers: 8
d. Golden fruit and white flowers: 44
How many map unit separate these genes?
7. The chi-square test measures what?
a. The binomial coefficient of a set of data.
b. How well the expected and observed data fit a specific model of hypothesis.
c. The degrees of freedom for any given experiment.
d. The expected outcome of genetic crosses.
8. If a chi-square value for a given set of data exceeds the theoretical value found in a chisquare table, it can be claimed that the
a. Observed data is consistent with that expected.
b. Original hypothesis was correct.
c. Sum of the expected and observed data is equal to 1.
d. Observed and expected data differ significantly, suggesting the model is wrong.