Biology: The Dynamic Science

Peter J. Russell, Paul E. Hertz, Beverly McMillan

Chapter 12

Mendel, Genes, and Inheritance - all with Video Answers

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Chapter Questions

Problem 1

The dominant $C$ allele of a gene that controls color in corn produces kernels with color; plants homozygous for a recessive $c$ allele of this gene have colorless or white kernels. What kinds of gametes, and in what proportions, would be produced by the plants in the following crosses? What seed color, and in what proportions, would be expected in the offspring of the crosses?
a. $\quad C C \times C c$
b. $\quad C c \times c c$
c. $\quad C c \times C c$

Emili Wallace

Emili Wallace

Numerade Educator

Problem 2

In peas, the allele Le produces tall plants and the allele le produces dwarf plants. The $L e$ allele is dominant to le. If a tall plant is crossed with a dwarf, the offspring are distributed about equally between tall and dwarf plants. What are the genotypes of the parents?

Bryan Valdivia

Numerade Educator

Problem 3

One gene has the alleles $A$ and $a$; another gene has the alleles $B$ and $b$. For each of the following genotypes, what types of gametes will be produced, and in what proportions, if the two gene pairs assort independently?
a. $A A B B$
b.?? $B B$
c. Aabb
d. $A a B b$

Emili Wallace

Numerade Educator

Problem 4

What genotypes, and in what frequencies, will be present in the offspring from the following matings?
a. $ A A B B \times$ aa $B B$
b. Aa $B b \times$aabb
c. Aa $B B \times A A B b$
d. Aa $B b \times$AaBb

Josee Pacheco

Numerade Educator

Problem 5

In addition to the two genes in problem $4,$ assume you now study a third independently assorting gene that has the alleles $C$ and $c$. For each of the following genotypes, indicate what types of gametes will be produced:
a. $ A A B B C C$
b. $ A a B B C c$
c. $A a B B c c$
d. $A a B b C c$

Emili Wallace

Numerade Educator

Problem 6

In garden peas, the genotypes GG or Gg produce green pods and $g g$ produces yellow pods; $L e L e$ or $L$ ele plants are tall and lele e plants are dwarfed; $R R$ or $R r$ produce round seeds and $r r$ produces wrinkled seeds. If a plant of a true-breeding, tall variety with green pods and round seeds is crossed with a plant of a true-breeding, dwarf variety with yellow pods and wrinkled seeds, what phenotypes are expected, and in what ratios, in the $\mathrm{F}_{1}$ generation? What phenotypes, and in what ratios, are expected if $\mathrm{F}_{1}$ individuals are crossed (allowed to self-fertilize)?

Josee Pacheco

Numerade Educator

Problem 7

In cats, the genotype $A A$ produces tabby fur color; $A a$ is also a tabby, and $a a$ is black. Another gene at a different locus is epistatic to the gene for fur color. When present in its dominant $W$ form $(W W$ or $W w),$ this gene blocks the formation of fur color and all the offspring are white; $w w$ individuals develop normal fur color. What fur colors, and in what proportions, would you expect from the cross $A a W w \times A a W w ?$

Rabeya Zahid

Numerade Educator

Problem 8

Explain how individuals of an organism that are phenotypically alike can produce different ratios of progeny phenotypes.

Rabeya Zahid

Numerade Educator

Problem 9

The ability of humans to taste the bitter chemical phenylthiocarbamide (PTC) is a genetic trait. People with at least one copy of the normal, dominant allele of the $P T C$ gene can taste PTC; those who are homozygous for a mutant, recessive allele cannot taste it. Could two parents able to taste PTC have a nontaster child? Could nontaster parents have a child able to taste PTC? A pair of taster parents, both of whom had one parent able to taste PTC and one nontaster parent, are expecting their first child. What is the chance that the child will be able to taste PTC? Unable to taste PTC? Suppose the first child is a nontaster. What is the chance that their second child will also be unable to taste PTC?

Bryan Valdivia

Numerade Educator

Problem 10

A man is homozygous dominant for alleles at 10 different genes that assort independently. How many genotypically different types of sperm cells can he produce? A woman is homozygous recessive for the alleles of 8 of these 10 genes, but she is heterozygous for the other 2 genes. How many genotypically different types of eggs can she produce? What hypothesis can you suggest to describe the relationship between the number of different possible gametes and the number of heterozygous and homozygous genes that are present?

Joanna Quigley

Numerade Educator

Problem 11

In guinea pigs, an allele for rough fur $(R)$ is dominant over an allele for smooth fur $(r) ;$ an allele for black coat $(B)$ is dominant over that for white ( $b$ ). You have an animal with rough, black fur. What cross would you use to determine whether the animal is homozygous for these traits? What phenotype would you expect in the offspring if the animal is homozygous?

Bryan Valdivia

Numerade Educator

Problem 12

You cross a lima bean plant from a variety that breeds true for green pods with another lima bean from a variety that breeds true for yellow pods. You note that all the $\mathrm{F}_{1}$ plants have green pods. These green-pod $\mathrm{F}_{1}$ plants, when crossed, yield 675 plants with green pods and 217 with yellow pods. How many genes probably control pod color in this experiment? Give the alleles letter designations. Which is dominant?

Bryan Valdivia

Numerade Educator

Problem 13

Some recessive alleles have such a detrimental effect that they are lethal when present in both chromosomes of a pair. Homozygous recessives cannot survive and die at some point during embryonic development. Suppose that the allele $r$ is lethal in the homozygous $r r$ condition. What genotypic ratios would you expect among the living offspring of the following crosses?
a. $R R \times R r$
b. $\operatorname{Rr} \times R r$

Bryan Valdivia

Numerade Educator

Problem 14

In chickens, feathered legs are produced by a dominant allele $F$. Another allele $f$ of the same gene produces featherless legs. The dominant allele $P$ of a gene at a different locus produces pea combs; a recessive allele $p$ of this gene causes single combs. A breeder makes the following crosses with birds $1,2,3,$ and $4 ;$ all parents have both feathered legs and pea combs:
Cross Offspring $1 \times 2 \quad$ All feathered, pea comb
$1 \times 3 \quad 3 / 4$ feathered; $1 / 4$ featherless, all pea comb
$1 \times 4 \quad 9 / 16$ feathered, pea comb; $3 / 16$ featherless, pea comb $3 / 16$ feathered, single comb; $1 / 16$ featherless, single comb
What are the genotypes of the four birds?

Joanna Quigley

Numerade Educator

Problem 15

A mix-up in a hospital ward caused a mother with $\mathrm{O}$ and $\mathrm{MN}$ blood types to think that a baby given to her really belonged to someone else. Tests in the hospital showed that the doubting mother was able to taste PTC (see problem 9). The baby given to her had O and MN blood types and had no reaction when the bitter PTC chemical was placed on its tongue. The mother had four other children with the following blood types and tasting abilities for PTC:
1. type $A$ and $M N$ blood, taster
2. type $B$ and $N$ blood, nontaster
3. type A and M blood, taster
4. type $A$ and $N$ blood, taster
Without knowing the father's blood types and tasting ability, can you determine whether the child is really hers? (Assume that all her children have the same father.)

Nick Roster

Numerade Educator

Problem 16

Having malformed hands with shortened fingers is a dominant trait controlled by a single gene; people who are homozygous for the recessive allele have normal hands and fingers. Having woolly hair is a dominant trait controlled by a different gene; homozygous recessive individuals have normal, nonwoolly hair. Suppose a woman with normal hands and nonwoolly hair marries a man who has malformed hands and woolly hair. Their first child has normal hands and nonwoolly hair. What are the genotypes of the mother, the father, and the child? If this couple has a second child, what is the probability that it will have normal hands and woolly hair?

Bryan Valdivia

Numerade Educator

Problem 17

ABO blood type tests can be used to exclude paternity. Suppose a defendant who is the alleged father of a child takes a blood type test and the results do not exclude him as the father. Do the results indicate that he is the father?
What arguments could a lawyer make based on the test results to exclude the defendant from being the father? (Assume the tests were performed correctly.)

Rabeya Zahid

Numerade Educator

Problem 18

Imagine that you are a breeder of Labrador retriever dogs. Labs can be black, chocolate brown, or yellow. Suppose that a yellow Lab is donated to you and you need to know its genotype. You have a range of dogs with known genotypes. What cross would you make to determine the genotype of the donated dog? Explain how the resulting puppies show you the Lab's genotype.

Miwa Wenzel

Numerade Educator

Problem 19

How could an epistatic interaction shelter a harmful allele from the action of natural selection?

Emily Himsel

Numerade Educator