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Principles of Genetics

D. Peter Snustad, Michael J. Simmons

Chapter 3

Mendelism: The Basic Principles of Inheritance - all with Video Answers

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Chapter Questions

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Problem 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 dwarf parent.

Kaela Piechowicz
Kaela Piechowicz
Numerade Educator
01:29

Problem 2

Mendel crossed pea plants that produced round seeds with those that produced wrinkled seeds and self-fertilized the progeny. In the $\mathrm{F}_{2}$, he observed 5474 round seeds and 1850 wrinkled seeds. Using the letters $W$ and $w$ for the seed texture alleles, diagram Mendel's crosses, showing the genotypes of the plants in each generation. Are the results consistent with the Principle of Segregation?

Anand Jangid
Anand Jangid
Numerade Educator
05:01

Problem 3

A geneticist crossed wild, gray-colored mice with white (albino) mice. All the progeny were gray. These progeny were intercrossed to produce an $\mathrm{F}_{2},$ 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 the hypothesis.

Cody Delk
Cody Delk
Numerade Educator
03:31

Problem 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, $P$ 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?
(b) What proportion of the woman's children will have ptosis if she marries a man with normal eyelids?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
13:25

Problem 5

In pigeons, a dominant allele $C$ causes a checkered pattern in the feathers; its recessive allele $c$ produces a plain pattern. Feather coloration is controlled by an independently assorting gene; the dominant allele $B$ produces red feathers, and the recessive allele $b$ produces brown feathers. Birds from a true-breeding checkered, red variety are crossed to birds from a true-breeding plain, brown variety.
(a) Predict the phenotype of their progeny.
(b) If these progeny are intercrossed, what phenotypes will appear in the $\mathrm{F}_{2},$ and in what proportions?

Cody Delk
Cody Delk
Numerade Educator
08:40

Problem 6

In mice, the allele $C$ for colored fur is dominant over the allele $c$ for white fur, and the allele $V$ for normal behavior is dominant over the allele $v$ for waltzing behavior, a form of discoordination. Give the genotypes of the parents in each of the following crosses:
(a) Colored, normal mice mated with white, normal mice produced 29 colored, normal and 10 colored, waltzing progeny.
(b) Colored, normal mice mated with colored, normal mice produced 38 colored, normal, 15 colored, waltzing, 11 white, normal, and 4 white, waltzing progeny.
(c) Colored, normal mice mated with white, waltzing mice produced 8 colored, normal, 7 colored, waltzing, 9 white, normal, and 6 white, waltzing progeny.

Tracy Lin
Tracy Lin
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Problem 7

In rabbits, the dominant allele $B$ causes black fur and the recessive allele $b$ causes brown fur; for an independently assorting gene, the dominant allele $R$ causes long fur and the recessive allele $r(\text { for } \operatorname{rex})$ causes short fur. A homozygous rabbit with long, black fur is crossed with a rabbit with short, brown fur, and the offspring are intercrossed. In the $\mathrm{F}_{2},$ what proportion of the rabbits with long, black fur will be homozygous for both genes?

Kaela Piechowicz
Kaela Piechowicz
Numerade Educator
03:06

Problem 8

In shorthorn cattle, the genotype $R R$ causes a red coat, the genotype $r r$ causes a white coat, and the genotype $R r$ causes a roan coat. A breeder has red, white, and roan cows and bulls. What phenotypes might be expected from the following matings, and in what proportions?
(a) red $\times$ red;
(b) red $\times$ roan;
(c) red $\times$ white;
(d) $\operatorname{roan} \times$ roan

Cody Delk
Cody Delk
Numerade Educator
03:21

Problem 9

How many different kinds of $\mathrm{F}_{1}$ gametes, $\mathrm{F}_{2}$ genotypes, and $\mathrm{F}_{2}$ phenotypes would be expected from the following crosses:
(a) $A A \times a a$
(b) $A A B B \times a a b b$
(c) $A A B B C C \times a a b b c c$
(d) What general formulas are suggested by these answers?

Prashant Bana
Prashant Bana
Numerade Educator
11:25

Problem 10

A researcher studied six independently assorting genes in a plant. Each gene has a dominant and a recessive allele:
$R$ black stem, $r$ red stem; $D$ tall plant, $d$ dwarf plant; $C$ full pods, $c$ constricted pods; $O$ round fruit, $o$ oval fruit; $H$ hairless leaves, $b$ hairy leaves; $W$ purple flower, w white flower. From the cross
$(\mathrm{P} 1) R r D d c C O H b W w \times(\mathrm{P} 2) R r d d C c o o H b w w$,.(a) How many kinds of gametes can be formed by P1?
(b) How many genotypes are possible among the progeny of this cross?
(c) How many phenotypes are possible among the progeny?
(d) What is the probability of obtaining the $R r D d \propto O o b b w w$ genotype in the progeny?
(e) What is the probability of obtaining a black, dwarf, constricted, oval, hairy, purple phenotype in the progeny?

Jennifer Hudspeth
Jennifer Hudspeth
Numerade Educator
03:56

Problem 11

For each of the following situations, determine the degrees of freedom associated with the $\chi^{2}$ statistic and decide whether or not the observed $\chi^{2}$ value warrants acceptance or rejection of the hypothesized genetic ratio.

Josee Pacheco
Josee Pacheco
Numerade Educator
01:19

Problem 12

Mendel testcrossed pea plants grown from yellow, round $\mathrm{F}_{1}$ seeds to plants grown from green, wrinkled seeds and obtained the following results: 31 yellow, round; 26 green, round; 27 yellow, wrinkled; and 26 green, wrinkled. Are these results consistent with the hypothesis that seed color and seed texture are controlled by independently assorting genes, each segregating two alleles?

Prashant Bana
Prashant Bana
Numerade Educator
05:22

Problem 13

Perform a chi-square test to determine if an observed ratio of 30 tall: 20 dwarf pea plants is consistent with an expected ratio of 1: 1 from the cross $D d \times d d$

Alaina Golden
Alaina Golden
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06:28

Problem 14

Seed capsules of the Shepherd's purse are either triangular or ovoid. A cross between a plant with triangular seed capsules and a plant with ovoid seed capsules yielded $\mathrm{F}_{1}$, hybrids that all had triangular seed capsules. When these $F_{1}$ hybrids were intercrossed, they produced $80 \mathrm{F}_{2}$ plants, 72 of which had triangular seed capsules and 8 of which had ovoid seed capsules. Are these results consistent with the hypothesis that capsule shape is determined by a single gene with two alleles?

Jennifer Hudspeth
Jennifer Hudspeth
Numerade Educator
02:34

Problem 15

Albinism in humans is caused by a recessive allele $a$. From marriages between people known to be carriers $(A a)$ and people with albinism (aa), what proportion of the children would be expected to have albinism? Among three children, what is the chance of one without albinism and two with albinism?

Cody Delk
Cody Delk
Numerade Educator
01:42

Problem 16

If both husband and wife are known to be carriers of the allele for albinism, what is the chance of the following combinations in a family of four children: (a) all four unaffected; (b) three unaffected and one affected; (c) two unaffected and two affected; (d) one unaffected and three affected?

Jennifer Stoner
Jennifer Stoner
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07:35

Problem 17

In humans, cataracts in the eyes and fragility of the bones are caused by dominant alleles that assort independently. A man with cataracts and normal bones marries a woman without cataracts but with fragile bones. The man's father had normal eyes, and the woman's father had normal bones. What is the probability that the first child of this couple will
(a) be free from both abnormalities;
(b) have cataracts but not have fragile bones;
(c) have fragile bones but not have cataracts; (d) have both cataracts and fragile bones?

Cody Delk
Cody Delk
Numerade Educator
06:10

Problem 18

In generation $\mathrm{V}$ in the pedigree in Figure $3.15,$ what is the probability of observing seven children without the cancer-causing mutation and two children with this mutation among a total of nine children?

Rashmi Sinha
Rashmi Sinha
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00:59

Problem 19

If a man and a woman are heterozygous for a gene, and if they have three children, what is the chance that all three will also be heterozygous?

Cody Delk
Cody Delk
Numerade Educator
07:04

Problem 20

If four babies are born on a given day:
(a) What is the chance that two will be boys and two girls?
(b) What is the chance that all four will be girls?
(c) What combination of boys and girls among four babies is most likely?
(d) What is the chance that at least one baby will be a girl?

Jennifer Hudspeth
Jennifer Hudspeth
Numerade Educator
01:40

Problem 21

In a family of six children, what is the chance that at least three are girls?

Hailey Tomashek
Hailey Tomashek
Numerade Educator
01:15

Problem 22

The following pedigree shows the inheritance of a dominant trait. What is the chance that the offspring of the following matings will show the trait:
(a) $\mathrm{III}-1 \times \mathrm{III}-3 ;(\mathrm{b}) \mathrm{III}-2 \times \mathrm{III}-4 ?$

Michelle Bandeira
Michelle Bandeira
Numerade Educator
01:52

Problem 23

The following pedigree shows the inheritance of a recessive trait. Unless there is evidence to the contrary, assume that the individuals who have married into the family do not carry the recessive allele. What is the chance that the offspring of the following matings will show the trait:
(a) $\mathrm{III}-1 \times \mathrm{III}-12$
(b) $\Pi I-4 \times \Pi I-14$
(c) $\mathrm{III}-6 \times \mathrm{III}-13$
(d) $\Pi V-1 \times I V-2 ?$

Hailey Tomashek
Hailey Tomashek
Numerade Educator
01:22

Problem 24

In the following pedigrees, determine whether the trait is more likely to be due to a dominant or a recessive allele. Assume the trait is rare in the population.

Michelle Bandeira
Michelle Bandeira
Numerade Educator
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Problem 25

In pedigree $(b)$ of Problem 3.24 , what is the chance that the couple III-1 and III-2 will have an affected child? What is the chance that the couple $I V-2$ and $I V-3$ will have an affected child?

Katherine Kartheiser
Katherine Kartheiser
Numerade Educator
02:14

Problem 26

Peas heterozygous for three independently assorting genes were intercrossed.
(a) What proportion of the offspring will be homozygous for all three recessive alleles?
(b) What proportion of the offspring will be homozygous for all three genes?
(c) What proportion of the offspring will be homozygous for one gene and heterozygous for the other two?
(d) What proportion of the offspring will be homozygous for the recessive allele of at least one gene?

Alexander Cheng
Alexander Cheng
Numerade Educator
01:27

Problem 27

The following pedigree shows the inheritance of a recessive trait. What is the chance that the couple III-3 and III-4 will have an affected child?

Michelle Bandeira
Michelle Bandeira
Numerade Educator
04:56

Problem 28

A geneticist crosses tall pea plants with short pea plants. All the $\mathrm{F}_{1}$ plants are tall. The $\mathrm{F}_{1}$ plants are then allowed to self-fertilize, and the $\mathrm{F}_{2}$ plants are classified by height: 62 tall and 26 short. From these results, the geneticist concludes that shortness in peas is due to a recessive allele $(s)$ and that tallness is due to a dominant allele (S). On this hypothesis, $2 / 3$ of the tall $\mathrm{F}_{2}$ plants should be heterozygous $S s .$ To test this prediction, the geneticist uses pollen from each of the 62 tall plants to fertilize the ovules of emasculated flowers on short pea plants. The next year, three seeds from each of the 62 crosses are sown in the garden and the resulting plants are grown to maturity. If none of the three plants from a cross is short, the male parent is classified as having been homozygous $S S ;$ if at least one of the three plants from a cross is short, the male parent is classified as having been heterozygous Ss. Using this system of progeny testing, the geneticist concludes that 29 of the 62 tall $\mathrm{F}_{2}$ plants were homozygous $S S$ and that 33 of these plants were heterozygous $S s$.
(a) Using the chi-square procedure, evaluate these results for goodness of fit to the prediction that $2 / 3$ of the tall $\mathrm{F}_{2}$ plants should be heterozygous.
(b) Informed by what you read in A Milestone in Genetics:
Mendel's 1866 Paper (which you can find in the Student Companion site), explain why the geneticist's procedure for classifying tall $F_{2}$ plants by genotype is not definitive.
(c) Adjust for the uncertainty in the geneticist's classification procedure and calculate the expected frequencies of homozygotes and heterozygotes among the tall $\mathrm{F}_{2}$ plants.
(d) Evaluate the predictions obtained in
(c) using the chisquare procedure.

Grant Castaneda
Grant Castaneda
Numerade Educator
04:27

Problem 29

A researcher who has been studying albinism has identified a large group of families with four children in which at least one child shows albinism. None of the parents in this group of families shows albinism. Among the children, the ratio of those without albinism to those with albinism is $1.7: 1 .$ The researcher is surprised by this result because he thought that a 3: 1 ratio would be expected on the basis of Mendel's Principle of Segregation. Can you explain the apparently non-Mendelian segregation ratio in the researcher's data?

Rabeya Zahid
Rabeya Zahid
Numerade Educator