Chapter 3 Answers to Homework Problems
1, 3, 4, 5, 7, 10, 12, 16, 17, 19, 22, 23, 24, 25, 29
1. Questions and Problems, 3-1
On the basis of Mendel’s observations, predict the results from the following crosses with peas: (a) a tall
(dominant and homozygous) variety crossed with a dwarf variety; (b) the progeny of (a) self-fertilized; (c)
the progeny from (a) crossed with the original tall parent; (d) the progeny of (a) crossed with the original
Ans: (a) All tall; (b) 3/4 tall, 1/4 dwarf; (c) all tall; (d) 1/2 tall, 1/2 dwarf.
3. Questions and Problems, 3-3
A geneticist crossed wild, gray-colored mice with white (albino) mice. All the progeny were gray. These
progeny were intercrossed to produce an F
, which consisted of 198 gray and 72 white mice. Propose an
hypothesis to explain these results, diagram the crosses, and compare the results with the predictions of
Ans: The data suggest that coat color is controlled by a single gene with two alleles,
(albino), and that
is dominant over
. On this hypothesis, the crosses are: gray (
) > F
> 3/4 gray (2
), 1/4 albino (
). The expected results in the F
are 203 gray, 67
albino. To compare the observed and expected results, compute χ
with one degree of freedom: (198
/203 + (67 … 72)
/72 = 0.470, which is not significant at the 5% level. Thus, the results are
consistent with the hypothesis.
The publisher’s answer has a mistake in it.
As there are 270 progeny, the expected numbers from a
3:1 ratio are 202.5 and 67.5.
It is best not to round these.
/202.5 + (72-67.5)
= 0.1 +0.3 = 0.4.
The ultimate conclusion is the same.
The results are consistent with the hypothesis.
Questions and Problems, 3-4
A woman has a rare abnormality of the eyelids called ptosis, which prevents her from opening her eyes
completely. This condition is caused by a dominant allele,
The woman’s father had ptosis, but her
mother had normal eyelids. Her father’s mother had normal eyelids.
(a) What are the genotypes of the woman, her father, and her mother?