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Essentials of Genetics

William S. Klug, Michael R. Cummings, Charlotte A. Spencer

Chapter 4

Modification of Mendelian Ratios - all with Video Answers

Educators

Chapter Questions

03:36

Problem 1

In this chapter, we focused on many extensions and modifications of Mendellan principles and ratios. In the process, we encountered many opportunities to consider how this information was acquired. Answer the following fundamental questions:
(a) How were early geneticists able to ascertain inheritance patterns that did not fit typical Mendelian ratios?
(b) How did geneticists determine that inheritance of some phenotypic characteristics involves the interactions of two or more gene pairs? How were they able to determine how many gene pairs were involved?
(c) How do we know that specific genes are located on the sexdetermining chromosomes rather than on autosomes?
(d) For genes whose expression seems to be tied to the gender of individuals, how do we know whether a gene is X-linked in contrast to exhibiting sex-limited or sex-influenced inheritance?
(e) How was extranuclear inheritance discovered?

Celine Ibrahim
Celine Ibrahim
Numerade Educator
07:02

Problem 2

Review the Chapter Concepts list on page $53 .$ These all relate to exceptions to the inheritance patterns encountered by Mendel. Write a short essay that explains why multiple and lethal alleles often result in a modification of the classic Mendelian monohybrid and dihybrid ratios.

Jessica Honkomp
Jessica Honkomp
Numerade Educator
02:12

Problem 3

In Shorthorn cattle, coat color may be red, white, or roan. Roan is an intermediate phenotype expressed as a mixture of red and white hairs. The following data are obtained from various crosses:
red $\times$ red $\longrightarrow$ all red white $\times$ white $\longrightarrow$ all white red $\times$ white $\longrightarrow$ all roan
\[\text { roan } \times \operatorname{roan} \longrightarrow 1 / 4 \text { red: } 1 / 2\]
roan: $1 / 4$ white
(a) How is coat color inherited? What are the genotypes of parents and offspring for each cross?
(b) Does the roan phenotype illustrate a case of incomplete dominance or a case of codominance? Explain.

Bryan Valdivia
Bryan Valdivia
Numerade Educator
01:03

Problem 4

With regard to the ABO blood types in humans, determine the genotypes of the male parent and female parent:
Male parent: blood type B whose mother was type O Female parent: blood type A whose father was type B
Predict the blood types of the offspring that this couple may have and the expected ratio of each.

Christina Sorrentino
Christina Sorrentino
Numerade Educator
02:22

Problem 5

In foxes, two alleles of a single gene, $P$ and $p,$ may result in lethality $(P P),$ platinum coat $(P p),$ or silver coat $(p p) .$ What ratio is obtained when platinum foxes are interbred? Is the $P$ allele behaving dominantly or recessively in causing (a) lethality; platinum coat color?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
11:10

Problem 6

Three gene pairs located on separate autosomes determine flower color and shape as well as plant height. The first pair exhibits incomplete dominance, where color can be red, pink (the heterozygote), or white. The second pair leads to the dominant personate or recessive peloric flower shape, while the third gene pair produces either the dominant tall trait or the recessive dwarf trait. Homozygous plants that are red, personate, and tall are crossed with those that are white, peloric, and dwarf. Determine the $F_{1}$ genotype(s) and phenotype(s). If the $F_{1}$ plants are inter. bred, what proportion of the offspring will exhibit the same phenotype as the $\mathrm{P}_{1}$ plants?

Khalida Dawar
Khalida Dawar
Numerade Educator
02:21

Problem 7

As in the plants of Problem $6,$ color may be red, white, or pink; and flower shape may be personate or peloric. Determine the $\mathrm{P}_{1}$ and $\mathrm{P}_{1}$, genotypes for the following crosses:

Eric Goldman
Eric Goldman
Numerade Educator
05:12

Problem 8

The following genotypes of two independently assorting autosomal genes determine coat color in rats:
$A-B-(\text { gray }) ; A-b b$ (yellow) $; a a B-$ (black); $a a b b$ (cream) A third gene pair on a separate autosome determines whether any color will be produced. The $C C$ and $C c$ genotypes allow color according to the expression of the $A$ and $B$ alleles. However, the ce genotype results in allbino rats regardless of the $A$ and $B$ alleles present. Determine the $F_{1}$ phenotypic ratio of the following crosses: (a)AAbbCC $\times$ aaBBcc;
(b) $A a B B c c \times A A B b c c$
(c) $A a B b C c \times A a B b c c$

Jessica Wooten
Jessica Wooten
Numerade Educator
01:47

Problem 9

Given the inheritance pattern of coat color in rats described in Problem $8,$ predict the genotype and phenotype of the parents that produced the following $\mathrm{P}_{1}$ offspring: (a) $9 / 16$ gray: $3 / 16$ yellow: $3 / 16$ black: $1 / 16$ cream; (b) $9 / 16$ gray: $3 / 16$ yellow: $4 / 16$ albino; (c) 27/64 gray: 16/64 albino: 9/64 yellow: 9/64 black: $3 / 64$ cream.

Anand Jangid
Anand Jangid
Numerade Educator
01:15

Problem 10

A husband and wife have normal vision, although both of their fathers are red-green color-blind, inherited as an X-linked recessive condition. What is the probability that their first child will be
(a) a normal son,
(b) a normal daughter,
(c) a color-blind son,
(d) a color-blind daughter?

Zachary Papazian
Zachary Papazian
Numerade Educator
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Problem 11

In humans, the ABO blood type is under the control of autosomal multiple alleles. Red-green color blindness is a recessive X-linked trait. If two parents who are both type A and have normal vision produce a son who is color-blind and type $0,$ what is the probability that their next child will be a female who has normal vision and is type $0 ?$

Kaela Piechowicz
Kaela Piechowicz
Numerade Educator
03:43

Problem 12

In goats, development of the beard is due to a recessive gene. The following cross involving true-breeding goats was made and carried to the $\mathrm{F}_{2}$ generation:
$P_{1}:$ bearded female $\times$ beardless male
$\mathrm{F}_{1}:$ all bearded males and beardless females
\[
\mathrm{P}_{1} \times \mathrm{F}_{1} \longrightarrow\left\{\begin{array}{l}
1 / 8 \text { beardless males } \\
3 / 8 \text { bearded males } \\
3 / 8 \text { beardless females } \\
1 / 8 \text { bearded females }\end{array}\right.\]
Offer an explanation for the inheritance and expression of this trait, diagramming the cross. Propose one or more crosses to test your hypothesis.

Alexander Cheng
Alexander Cheng
Numerade Educator
04:19

Problem 13

In cats, orange coat color is determined by the $b$ allele, and black coat color is determined by the $B$ allele. The heterozygous condition results in a coat pattern known as tortoiseshell, These genes are X-linked. What kinds of offspring would be expected from a cross of a black male and a tortoiseshell female? What are the chances of getting a tortoiseshell male?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
05:41

Problem 14

In Drosophila, an $\mathrm{X}$ -linked recessive mutation, scalloped (sd), causes irregular wing margins. Diagram the $F_{1}$ and $F_{2}$ results if (a) a scalloped female is crossed with a normal male; (b) a scalloped male is crossed with a normal female. Compare these results to those that would be obtained if the scalloped gene were autosomal.

John Barone
John Barone
Numerade Educator
07:25

Problem 15

Another recessive mutation in Drosophila, ebony (e), is on an autosome (chromosome 3 ) and causes darkening of the body compared with wild-type flies. What phenotypic $F_{1}$ and $\mathrm{F}_{2}$ male and female ratios will result if a scalloped-winged female with normal body color is crossed with a normal-winged ebony male? Work this problem by both the Punnett square method and the forked-line method.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
06:08

Problem 16

While vermilion is X-linked in Drosophila and causes eye color to be bright red, brown is an autosomal recessive mutation that causes the eye to be brown. Flies carrying both mutations lose all pigmentation and are white-eyed. Predict the $F_{1}$ and $F_{2}$ results of the following crosses:
(a) vermilion females $\times$ brown males
(b) brown females $\times$ vermilion males
(c) white females $\times$ wild males

Khalida Dawar
Khalida Dawar
Numerade Educator
05:02

Problem 17

In pigs, coat color may be sandy, red, or white, A geneticist spent several years mating true-breeding pigs of all different color combinations, even obtaining true-breeding lines from different parts of the country. For crosses 1 and 4 in the following table, she encountered a major problem: her computer crashed and she lost the $\mathrm{F}_{2}$ data. She nevertheless persevered and, using the limited data shown here, was able to predict the mode of inheritance and the number of genes involved, as well as to assign genotypes to each coat color. Attempt to duplicate her analysis, based on the available data generated from the crosses shown.
$$\begin{array}{clll}
\text { Cross } & \mathbf{P}_{\mathbf{1}} & \mathbf{F}_{\mathbf{1}} & \mathbf{F}_{\mathbf{2}} \\
1 & \operatorname{sand} y \times \operatorname{sand} y & \text { All red } & \text { Data lost } \\
2 & \text { red } \times \text { sandy } & \text { All red } & 3 / 4 \text { red: } 1 / 4 \text { sandy } \\
3 & \text { sandy } \times \text { white } & \text { All sandy } & 3 / 4 \text { sandy }=1 / 4 \text { white } \\
4 & \text { white } \times \text { red } & \text { All red } & \text { Data lost }\end{array}$$
When you have formulated a hypothesis to explain the mode
of inheritance and assigned genotypes to the respective coat colors, predict the outcomes of the $\mathrm{F}_{2}$ generations where the data were lost.

Celine Ibrahim
Celine Ibrahim
Numerade Educator
02:54

Problem 18

A geneticist from an alien planet that prohibits genetic research brought with him two true-breeding lines of frogs. One frog line croaks by uttering "rib-it rib-it" and has purple eyes. The other frog line croaks by muttering "knee-deep knee-deep" and has green eyes. He mated the two frog lines, producing $F_{1}$ frogs that were all utterers with blue eyes. A large $\mathrm{F}_{2}$ generation then yielded the following ratios:
$27 / 64$ blue, utterer
$12 / 64$ green, utterer
$9 / 64$ blue, mutterer
$9 / 64$ purple, utterer
$4 / 64$ green, mutterer
$3 / 64$ purple, mutterer
(a) How many total gene pairs are involved in the inheritance of both eye color and croaking?
(b) Of these, how many control eye color, and how many control croaking?
(c) Assign gene symbols for all phenotypes, and indicate the genotypes of the $P_{1}, F_{1},$ and $F_{2}$ frogs.
(d) After many years, the frog geneticist isolated true-breeding lines of all six $\mathrm{F}_{2}$ phenotypes. Indicate the $\mathrm{F}_{1}$ and $\mathrm{F}_{2}$ phenotypic ratios of a cross between a blue, mutterer and a purple, utterer.

Rabeya Zahid
Rabeya Zahid
Numerade Educator
01:12

Problem 19

In another cross, the frog geneticist from Problem 18 mated two purple, utterers with the results shown here. What were the genotypes of the parents?
$9 / 16$ purple, utterers
$3 / 16$ purple, mutterers
$3 / 16$ green, utterers
$1 / 16$ green, mutterers

Jonathan Temple
Jonathan Temple
Numerade Educator
02:12

Problem 20

In cattle, coats may be solid white, solid black, or black-and-white spotted. When true-breeding solid whites are mated with truebreeding solid blacks, the $\mathrm{F}_{1}$ generation consists of all solid white individuals. After many $\mathrm{F}_{1} \times \mathrm{F}_{1}$ matings, the following ratio was observed in the $\mathrm{F}_{2}$ generation:
$12 / 16$ solid white
$3 / 16$ black-and-white spotted
$1 / 16$ solid black
Explain the mode of inheritance governing coat color by determining how many gene pairs are involved and which genotypes yield which phenotypes. Is it possible to isolate a true-breeding strain of black-and-white spotted cattle? If so, what genotype would they have? If not, explain why not.

Bryan Valdivia
Bryan Valdivia
Numerade Educator
05:19

Problem 21

Consider the following three pedigrees, all involving the same human trait:
(a) Which sets of conditions, if any, can be excluded?
dominant and X-linked
dominant and autosomal
recessive and X-linked
recessive and autosomal
(b) For any set of conditions that you excluded, indicate the single individual in generation II $(1-9)$ that was instrumental in your decision to exclude that condition. If none were excluded, answer "none apply."
(c) Given your conclusions in parts (a) and (b), indicate the genotype of individuals $\|-1,$ II- $6,$ and $\Pi$ - 9 . If more than one possibility applies, list all possibilities. Use the symbols $A$ and $a$ for the genotypes.

Shiksha Dutta
Shiksha Dutta
Numerade Educator
05:31

Problem 22

Labrador retrievers may be black, brown, or golden in color (see the chapter opening photograph on $\mathrm{p} .53$ ). Although each color may breed true, many different outcomes occur if numerous litters are examined from a variety of matings, where the parents are not necessarily true-breeding. The following results show some of the possibilities. Propose a mode of inheritance that is consistent with these data, and indicate the corresponding genotypes of the parents in each mating. Indicate as well the genotypes of dogs that breed true for each color.
(a) black $\times$ brown $\longrightarrow$ all black
(b) black $\times$ brown $\longrightarrow \quad 1 / 2$ black
$1 / 2$ brown
(c) black $\times$ brown $\longrightarrow \quad 3 / 4$ black
$1 / 4$ golden
(d) black $\quad \times$ golden $\longrightarrow \quad$ all black
(e) black $\times$ golden $\longrightarrow \quad 4 / 8$ golden 318 black
$1 / 8$ brown
(f) black $\times$ golden $\longrightarrow \quad 2 / 4$ golden $1 / 4$ black
$1 / 4$ brown
(8) brown $\times$ brown $\longrightarrow \quad 3 / 4$ brown $1 / 4$ golden
(h) black
$\times$ black $\longrightarrow 9 / 16$ black
$4 / 16$ golden $3 / 16$ brown

John Barone
John Barone
Numerade Educator
01:17

Problem 23

Three autosomal recessive mutations in Drosophila, all with tan eye color $(r 1, r 2, \text { and } r 3),$ are independently isolated and sub jected to complementation analysis. Of the results shown below, which, if any, are alleles of one another? Predict the results of the cross that is not shown-that is, $r 2 \times r 3$
Cross 1:
$r 1 \times r 2 \longrightarrow \mathrm{F}_{1}:$ all wild-type eyes
Cross 2:
$r 1 \times r 3 \longrightarrow \mathrm{F}_{1}:$ all tan eyes

Hailey Tomashek
Hailey Tomashek
Numerade Educator
05:34

Problem 24

Horses can be cremello (a light cream color), chestnut (a reddish brown color), or palomino (a golden color with white in the horse's tail and mane).Of these phenotypes, only palominos never breed true. The following results have been observed:
(a) From these results, determine the mode of inheritance by assigning gene symbols and indicating which genotypes yield which phenotypes.
(b) Predict the $\mathrm{F}_{1}$ and $\mathrm{F}_{2}$ results of many initial matings between cremello and chestnut horses.

Bryan Lynn
Bryan Lynn
Numerade Educator
05:12

Problem 25

Pigment in the mouse is produced only when the $C$ allele is present. Individuals of the $c c$ genotype have no color. If color is present, it may be determined by the $A$ and $a$ alleles. AA or Aa results in agouti color, whereas aa results in black coats.
(a) What $F_{1}$ and $F_{2}$ genotypic and phenotypic ratios are obtained from a cross between $A A C C$ and aace mice?
(b) In the three crosses shown here between agouti females whose genotypes were unknown and males of the aacc genotype, what are the genotypes of the female parents for each of the following phenotypic ratios?
(1) 8 agouti
(2) 9 agouti
(3) 4 agouti 8 colorless
10 black $\quad 5$ black
10 colorless

Jessica Wooten
Jessica Wooten
Numerade Educator
04:58

Problem 26

Five human matings numbered $1-5$ are shown in the following table. Included are both maternal and paternal phenotypes for ABO and MN blood-group antigen status.
Each mating resulted in one of the five offspring shown to the right (a-e). Match each offspring with one correct set of parents, using each parental set only once. Is there more than one set of correct answers?

Shiksha Dutta
Shiksha Dutta
Numerade Educator
03:54

Problem 27

Two mothers give birth to sons at the same time at a busy urban hospital. The son of mother 1 has hemophilia, a disease caused by an X-linked recessive allele. Neither parent has the disease. Mother 2 has a son without hemophilia, despite the fact that the father has hemophilia. Several years later, couple 1 sues the hospital, claiming that these two newborns were swapped in the nursery following their birth. As a genetic counselor, you are called to testify. What information can you provide the jury concerning the allegation?

Chelsi Marolf
Chelsi Marolf
Numerade Educator
02:16

Problem 28

In Dexter and Kerry cattle, animals may be polled (hornless) or horned. The Dexter animals have short legs, whereas the Kerry animals have long legs. When many offspring were obtained from matings between polled Kerrys and horned Dexters, half were found to be polled Dexters and half polled Kerrys. When these two types of $\mathrm{F}_{1}$ cattle were mated to one another, the following $\mathrm{F}_{2}$ data were obtained:
$3 / 8$ polled Dexters 3/8 polled Kerrys
$1 / 8$ horned Dexters $1 / 8$ horned Kerrys
A geneticist was puzzled by these data and interviewed farmers who had bred these cattle for decades. She learned that Kerrys were true-breeding. Dexters, on the other hand, were not truebreeding and never produced as many offspring as Kerrys. Provide a genetic explanation for these observations.

Hailey Tomashek
Hailey Tomashek
Numerade Educator
01:33

Problem 29

What genetic criteria distinguish a case of extranuclear inheritance from (a) a case of Mendelian autosomal inheritance; (b) a case of $\mathrm{X}$ -linked inheritance?

Jessica Honkomp
Jessica Honkomp
Numerade Educator
00:22

Problem 30

The specification of the anterior-posterior axis in Drosophila embryos is initially controlled by various gene products that are synthesized and stored in the mature egg following oogenesis. Mutations in these genes result in abnormalitics of the axis during embryogenesis, illustrating maternal effect. How do such mutations vary from those involved in organelle heredity that illustrate extranuclear inheritance? Devise a set of parallel crosses and expected outcomes involving mutant genes that contrast maternal effect and organelle heredity.

Sam Limsuwannarot
Sam Limsuwannarot
Numerade Educator
00:22

Problem 31

The specification of the anterior-posterior axis in Drosophila embryos is initially controlled by various gene products that are synthesized and stored in the mature egg following oogenesis. Mutations in these genes result in abnormalitics of the axis during embryogenesis, illustrating maternal effect. How do such mutations vary from those involved in organelle heredity that illustrate extranuclear inheritance? Devise a set of parallel crosses and expected outcomes involving mutant genes that contrast maternal effect and organelle heredity.

Sam Limsuwannarot
Sam Limsuwannarot
Numerade Educator
01:26

Problem 32

Students taking a genetics exam were expected to answer the following question by converting data to a "meaningful ratio" and then solving the problem. The instructor assumed that the final ratio would reflect two gene pairs, and most correct answers did. Here is the exam question:
"Flowers may be white, orange, or brown. When plants with white flowers are crossed with plants with brown flowers, all the $F_{1}$ flowers are white. For $F_{2}$ flowers, the following data were obtained:
Convert the $F_{2}$ data to a meaningful ratio that allows you to explain the inheritance of color. Determine the number of genes involved and the genotypes that yield each phenotype."
(a) Solve the problem for two gene pairs. What is the final $\mathrm{F}_{2}$ ratio?
(b) A number of students failed to reduce the ratio for two gene pairs as described above and solved the problem using three gene pairs. When examined carefully, their solution was deemed a valid response by the instructor. Solve the problem using three gene pairs.

Anand Jangid
Anand Jangid
Numerade Educator
02:40

Problem 33

In four o'clock plants, many flower colors are observed. In a cross involving two true-breeding strains, one crimson and the other white, all of the $P_{1}$ generation were rose color. In the $F_{2}$, four new phenotypes appeared along with the $P_{1}$ and $F_{1}$ parental colors.
The following ratio was obtaincd:
$1 / 16$ erimson
$2 / 16$ orange
$1 / 16$ yellow
$2 / 16$ magenta
$4 / 16$ rose
$2 / 16$ pale yellow
$4 / 16$ white
Propose an explanation for the inheritance of these flower colors.

Bryan Valdivia
Bryan Valdivia
Numerade Educator
View

Problem 34

Below is a partlal pedigree of hemophilia in the British Royal Family descended from Queen Victoria, who is belicved to be the original "carrier" in this pedigree. Analyze the pedigree and indicate which females are also certain to be carriers. What is the probability that Princess Irene is a carrier?

Kaela Piechowicz
Kaela Piechowicz
Numerade Educator