Page 49 - Genetics_From_Genes_to_Genomes_6th_FULL_Part1

Problems 41

For parts (c–g), assume that none of the children is (Yellow and round are dominant.) What is the probabil-
a twin. ity that all seven peas in the pod are yellow and round?
c. If Susan and her husband have four children, what 25. The achoo syndrome (sneezing in response to bright
is the probability that none of the four will have light) and trembling chin (triggered by anxiety) are
galactosemia? both dominant traits in humans.
d. If the couple has four children, what is the probabil- a. What is the probability that the first child of parents
ity that at least one child will have galactosemia? who are heterozygous for both the achoo gene and
e. If the couple has four children, what is the proba- trembling chin will have achoo syndrome but lack
bility that the first two will have galactosemia and the trembling chin?
the second two will not? b. What is the probability that the first child will have
f. If the couple has three children, what is the proba- neither achoo syndrome nor trembling chin?
bility that two of the children will have galactose- 26. A pea plant from a pure-breeding strain that is tall,
mia and one will not, regardless of order? has green pods, and has purple flowers that are termi-
g. If the couple has four children with galactosemia, nal is crossed to a plant from a pure-breeding strain
what is the probability that their next child will that is dwarf, has yellow pods, and has white flowers
have galactosemia? that are axial. The F 1 plants are all tall and have pur-
21. Albinism is a condition in which pigmentation is ple axial flowers as well as green pods.
lacking. In humans, the result is white hair, nonpig- a. What phenotypes do you expect to see in the F 2 ?
mented skin, and pink eyes. The trait in humans is b. What phenotypes and ratios would you predict in
caused by a recessive allele. Two normal parents the progeny from crossing an F 1 plant to the dwarf
have an albino child. What are the parents’ genotypes? parent?
What is the probability that the next child will be 27. The following table shows the results of different
albino? matings between jimsonweed plants that had either
22. A cross between two pea plants, both of which grew purple or white flowers and spiny or smooth pods.
from yellow round seeds, gave the following numbers Determine the dominant allele for the two traits and
of seeds: 156 yellow round and 54 yellow wrinkled. indicate the genotypes of the parents for each of the
What are the genotypes of the parent plants? (Yellow crosses.
and round are dominant traits.)
23. A third-grader decided to breed guinea pigs for her Parents Offspring
school science project. She went to a pet store and Purple White Purple White
bought a male with smooth black fur and a female Spiny Spiny Smooth Smooth
with rough white fur. She wanted to study the inheri- a. purple spiny × purple spiny 94 32 28 11
tance of those features and was sorry to see that the b. purple spiny × purple smooth 40 0 38 0
first litter of eight contained only rough black ani- c. purple spiny × white spiny 34 30 0 0
mals. To her disappointment, the second litter from d. purple spiny × white spiny 89 92 31 27
those same parents contained seven rough black ani- e. purple smooth × purple smooth 0 0 36 11
mals. Soon the first litter had begun to produce F 2 off- f. white spiny × white spiny 0 45 0 16
spring, and they showed a variety of coat types.
Before long, the child had 125 F 2 guinea pigs. Eight 28. A pea plant heterozygous for plant height, pod
of them had smooth white coats, 25 had smooth black shape, and flower color was selfed. The progeny
coats, 23 were rough and white, and 69 were rough consisted of 272 tall, inflated pods, purple flowers;
and black. 92 tall, inflated, white flowers; 88 tall, flat pods,
a. How are the coat color and texture characteristics purple; 93 dwarf, inflated, purple; 35 tall, flat, white;
inherited? What evidence supports your 31 dwarf, inflated, white; 29 dwarf, flat, purple;
conclusions? 11 dwarf, flat, white. Which alleles are dominant
b. What phenotypes and proportions of offspring in this cross?
should the girl expect if she mates one of the 29. In the fruit fly Drosophila melanogaster, the follow-
smooth white F 2 females to an F 1 male? ing genes and mutations are known:
24. The self-fertilization of an F 1 pea plant produced from Wing size: recessive allele for tiny wings t; dominant
a parent plant homozygous for yellow and wrinkled allele for normal wings T.
seeds and a parent homozygous for green and round Eye shape: recessive allele for narrow eyes n;
seeds resulted in a pod containing seven F 2 peas. dominant allele for normal (oval) eyes N.