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Genetics: From Genes to Genomes

Leland Hartwell, Michael L. Goldberg, Janice Fischer

Chapter 2

Mendel's Principles of Heredity - all with Video Answers

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Chapter Questions

09:16

Problem 1

For each of the terms in the left column, choose the best matching phrase in the right column.
$$ \text { a phenotype } \quad \quad\quad\quad\quad \text { 1. having two identical alleles of a given gene } $$
$$ \text { b. alleles } \quad \quad\quad\quad\quad \text { 2. the allele expressed in the phenotype of the heterozygote } $$
$$ \text { c. independent assortment } \quad \quad\quad\quad\quad \text { 3. alternate forms of a gene } $$
$$ \text { d. gametes } \quad \quad\quad\quad\quad \text { 4. observable characteristic } $$
$$ \text { e. gene } \quad \quad\quad\quad\quad \text { 5. a cross between individuals both heterozygous for two genes } $$
$$ \text { f. segregation} \quad \quad\quad\quad\quad \text { $6 .$ alleles of one gene separate into gametes randomly with respect to alleles of other
genes } $$
$$ \text { g. heterozygote } \quad \quad\quad\quad\quad \text { 7. reproductive cells containing only one copy of each gene } $$
$$ \text { h. dominant } \quad \quad\quad\quad\quad \text { 8. the allele that does not contribute to the
phenotype of the heterozygote } $$
$$ \text { i. $F_{1}$ } \quad \quad\quad\quad\quad \text { 9. the cross of an individual of ambiguous genotype with a homozygous recessive individual} $$
$$ \text { j. testcross } \quad \quad\quad\quad\quad \text { 10. an individual with two different alleles
of a gene } $$
$$ \text { k. genotype } \quad \quad\quad\quad\quad \text { 11. the heritable entity that determines a characteristic } $$
$$ \text { l. recessive } \quad \quad\quad\quad\quad \text { 12. the alleles an individual has } $$
$$ \text { $\mathrm{m}$ dihybrid cross } \quad \quad\quad\quad\quad \text { 13. the separation of the two alleles of a gene into different gametes } $$
$$ \text { $\mathrm{m}$ dihybrid cross } \quad \quad\quad\quad\quad \text { 14. offspring of the P generation } $$

Jenny Wu
Jenny Wu
Numerade Educator
02:58

Problem 2

During the millennia in which selective breeding was practiced, why did breeders fail to uncover the principle that traits are governed by discrete units of inheritance (that is, by genes)?

Syed Vasi
Syed Vasi
Numerade Educator
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Problem 3

Describe the characteristics of the garden pea that made it a good organism for Mendel's analysis of the basic principles of inheritance. Evaluate how easy or difficult it would be to make a similar study of inheritance in humans by considering the same attributes you described for the pea.

Tom Comey
Tom Comey
Numerade Educator
03:34

Problem 4

An albino corn snake is crossed with a normal-colored corn snake. The offspring are all normal-colored. When these first-generation progeny snakes are crossed among themselves, they produce 32 normalcolored snakes and 10 albino snakes.
a. How do you know that only a single gene is responsible for the color differences between these snakes?
b. Which of these phenotypes is controlled by the dominant allele?
c. A normal-colored female snake is involved in a testcross. This cross produces 10 normal-colored and 11 albino offspring. What are the genotypes of the parents and the offspring?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
02:34

Problem 5

Two short-haired cats mate and produce six shorthaired and two long-haired kittens. What does this information suggest about how hair length is inherited?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
02:36

Problem 6

Piebald spotting is a condition found in humans in which there are patches of skin that lack pigmentation. The condition results from the inability of pigment-producing cells to migrate properly during development. Two adults with piebald spotting have one child who has this trait and a second child with normal skin pigmentation.
a. Is the piebald spotting trait dominant or recessive? What information led you to this answer?
b. What are the genotypes of the parents?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
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Problem 7

As a Drosophila research geneticist, you keep stocks of flies of specific genotypes. You have a fly that has normal wings (dominant phenotype). Flies with short wings are homozygous for a recessive allele of the wing-length gene. You need to know if this fly with normal wings is pure-breeding or heterozygous for the wing-length trait. What cross would you do to determine the genotype, and what results would you expect for each possible genotype?

Tom Comey
Tom Comey
Numerade Educator
04:24

Problem 8

A mutant cucumber plant has flowers that fail to open when mature. Crosses can be done with this plant by manually opening and pollinating the flowers with pollen from another plant. When closed $\times$ open crosses were done, all the $\mathrm{F}_{1}$ progeny were open. The $\mathrm{F}_{2}$ plants were 145 open and 59 closed. A cross of closed $\times \mathrm{F}_{1}$ gave 81 open and 77 closed. How is the closed trait inherited? What evidence led you to your conclusion?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
03:47

Problem 9

In a particular population of mice, certain individuals display a phenotype called short tail, which is inherited as a dominant trait. Some individuals display a recessive trait called dilute, which affects coat color. Which of these traits would be easier to eliminate from the population by selective breeding? Why?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
06:14

Problem 10

In humans, a dimple in the chin is a dominant characteristic controlled by a single gene.
a. $A$ man who does not have a chin dimple has children with a woman with a chin dimple whose mother lacked the dimple. What proportion of their children would be expected to have a chin dimple?
b. A man with a chin dimple and a woman who lacks the dimple produce a child who lacks a dimple. What is the man's genotype?
c. A man with a chin dimple and a nondimpled woman produce eight children, all having the chin dimple. Can you be certain of the man's genotype? Why or why not? What genotype is more likely, and why?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
10:10

Problem 11

Some inbred strains of the weedy plant Arabidopsis thaliana flower early in the growing season, but other strains flower at later times. Four different Arabdiposis plants $(1-4)$ were crossed, and the resulting progeny were tabulated as follows:
$$\begin{array}{ll}
\text { Mating } & \text { Progeny } \\
\hline 1 \times 2 & 77 \text { late }: 81 \text { early } \\
1 \times 3 & 134 \text { late } \\
1 \times 4 & 93 \text { late }: 32 \text { early } \\
2 \times 3 & 111 \text { late } \\
2 \times 4 & 65 \text { late }: 61 \text { early } \\
3 \times 4 & 126 \text { late }
\end{array}$$
a. Explain the genetic basis for the difference in flowering time. How do you know that among this group of plants, the flowering time trait is influenced by the action of a single gene? Which allele is dominant and which recessive?
b. Ascribe genotypes to the four plants.
c. What kinds of progeny would you expect if you allowed plants $1-4$ to self-fertilize, and in what ratios?

Jenny Wu
Jenny Wu
Numerade Educator
04:45

Problem 12

Among Native Americans, two types of earwax (cerumen) are seen, dry and sticky. A geneticist studied the inheritance of this trait by observing the types of offspring produced by different kinds of matings. He observed the following numbers:
a. How is earwax type inherited?
b. Why are no 3: 1 or 1: 1 ratios present in the data shown in the chart?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
04:51

Problem 13

Imagine you have just purchased a black stallion of unknown genotype. You mate him to a red mare, and she delivers twin foals, one red and one black. Can you tell from these results how color is inherited, assuming that alternative alleles of a single gene are involved? What crosses could you do to determine how color is inherited?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
05:51

Problem 14

If you roll a die (singular of dice), what is the probability you will roll: (a) a $6 ?(\mathrm{b})$ an even number?
(c) a number divisible by $3 ?$ (d) If you roll a pair of dice, what is the probability that you will roll two $6 \mathrm{s} ?(\mathrm{e})$ an even number on one and an odd number on the other? (f) matching numbers? (g) two numbers both over $4 ?$

Bryan Valdivia
Bryan Valdivia
Numerade Educator
03:19

Problem 15

In a standard deck of playing cards, four suits exist (red suits $=$ hearts and diamonds, black suits $=$ spades and clubs). Each suit has 13 cards: Ace (A), $2,3,4,5,6,7,8,9,10,$ and the face cards Jack (J) Queen (Q), and King (K). In a single draw, what is the probability that you will draw a face card? A red card? A red face card?

Melissa Donough
Melissa Donough
Numerade Educator
02:05

Problem 16

How many genetically different eggs could be formed by women with the following genotypes?
a. $A a b b C C D D$
b. $A A B b C c d d$
c. $A a B b$ cc $D d$
d. $A a B b C c D d$

Bryan Valdivia
Bryan Valdivia
Numerade Educator
08:48

Problem 17

What is the probability of producing a child that will phenotypically resemble either one of the two parents in the following four crosses? How many phenotypically different kinds of progeny could potentially result from each of the four crosses?
a. $A a B b C c D d \times a a b b c c d d$
b. aa bb cc dd $\times$AA BB CCDD
c. Aa Bb Cc Dd $\times$ Aa Bb Cc Dd
d. aa bb cc dd $\times$ aa bb cc dd

Bryan Valdivia
Bryan Valdivia
Numerade Educator
02:55

Problem 18

A mouse sperm of genotype $a B C D E$ fertilizes an egg of genotype $a b c D e .$ What are all the possibilities for the genotypes of (a) the zygote and (b) a sperm or egg produced by the mouse that develops from this fertilization?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
03:32

Problem 19

Your friend is pregnant with triplets. She thinks that it is equally likely that she will be the mother of 3 sons, 3 daughters, 2 sons and 1 daughter, or 1 son and 2 daughters. Is she correct? Explain. (Assume that each of the triplets is from a separate fertilization, and that boys and girls are equally likely.)

Bryan Valdivia
Bryan Valdivia
Numerade Educator
06:35

Problem 20

Galactosemia is a recessive human disease that is treatable by restricting lactose and glucose in the diet. Susan Smithers and her husband are both heterozygous for the galactosemia gene.
a. Susan is pregnant with twins. If she has fraternal (nonidentical) twins, what is the probability both of the twins will be girls who have galactosemia?
b. If the twins are identical, what is the probability that both will be girls and have galactosemia?
For parts (c-g), assume that none of the children is a twin.
c. If Susan and her husband have four children, what is the probability that none of the four will have galactosemia?
d. If the couple has four children, what is the probability that at least one child will have galactosemia?
e. If the couple has four children, what is the probability that the first two will have galactosemia and the second two will not?
f. If the couple has three children, what is the probability that two of the children will have galactosemia and one will not, regardless of order?
g. If the couple has four children with galactosemia, what is the probability that their next child will have galactosemia?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
01:17

Problem 21

Albinism is a condition in which pigmentation is lacking. In humans, the result is white hair, nonpigmented skin, and pink eyes. The trait in humans is caused by a recessive allele. Two normal parents have an albino child. What are the parents' genotypes? What is the probability that the next child will be albino?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
00:04

Problem 22

A cross between two pea plants, both of which grew from yellow round seeds, gave the following numbers of seeds: 156 yellow round and 54 yellow wrinkled. What are the genotypes of the parent plants? (Yellow and round are dominant traits.)

Dennis Howard
Dennis Howard
Numerade Educator
06:00

Problem 23

A third-grader decided to breed guinea pigs for her school science project. She went to a pet store and bought a male with smooth black fur and a female with rough white fur. She wanted to study the inheritance of those features and was sorry to see that the first litter of eight contained only rough black animals. To her disappointment, the second litter from those same parents contained seven rough black animals. Soon the first litter had begun to produce $\mathrm{F}_{2}$ offspring, and they showed a variety of coat types. Before long, the child had $125 \mathrm{F}_{2}$ guinea pigs. Eight of them had smooth white coats, 25 had smooth black coats, 23 were rough and white, and 69 were rough and black.
a. How are the coat color and texture characteristics inherited? What evidence supports your conclusions?
b. What phenotypes and proportions of offspring should the girl expect if she mates one of the smooth white $F_{2}$ females to an $F_{1}$ male?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
03:51

Problem 24

The self-fertilization of an $F_{1}$ pea plant produced from a parent plant homozygous for yellow and wrinkled seeds and a parent homozygous for green and round seeds resulted in a pod containing seven $\mathrm{F}_{2}$ peas. (Yellow and round are dominant.) What is the probability that all seven peas in the pod are yellow and round?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
02:29

Problem 25

The achoo syndrome (sneezing in response to bright light) and trembling chin (triggered by anxiety) are both dominant traits in humans.
a. What is the probability that the first child of parents who are heterozygous for both the achoo gene and trembling chin will have achoo syndrome but lack the trembling chin?
b. What is the probability that the first child will have neither achoo syndrome nor trembling chin?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
11:10

Problem 26

A pea plant from a pure-breeding strain that is tall, has green pods, and has purple flowers that are terminal is crossed to a plant from a pure-breeding strain that is dwarf, has yellow pods, and has white flowers that are axial. The $F_{1}$ plants are all tall and have purple axial flowers as well as green pods.
a. What phenotypes do you expect to see in the $\mathrm{F}_{2}$ ?
b. What phenotypes and ratios would you predict in the progeny from crossing an $\mathrm{F}_{1}$ plant to the dwarf parent?

Khalida Dawar
Khalida Dawar
Numerade Educator
09:18

Problem 27

The following table shows the results of different matings between jimsonweed plants that had either purple or white flowers and spiny or smooth pods. Determine the dominant allele for the two traits and indicate the genotypes of the parents for each of the crosses.
$$\begin{array}{ccccc}
& \text { Parents } & & {}{} {\text { Offspring }} \\
\hline & \begin{array}{c}
\text { Purple } \\
\text { Spiny }
\end{array} & \begin{array}{c}
\text { White } \\
\text { Spiny }
\end{array} & \begin{array}{c}
\text { Purple } \\
\text { Smooth }
\end{array} & \begin{array}{c}
\text { White } \\
\text { Smooth }
\end{array} \\
\hline \text { a. purple spiny } \times \text { purple spiny } & 94 & 32 & 28 & 11 \\
\text { b. purple spiny } \times \text { purple smooth } & 40 & 0 & 38 & 0 \\
\text { c. purple spiny } \times \text { white spiny } & 34 & 30 & 0 & 0 \\
\text { d. purple spiny } \times \text { white spiny } & 89 & 92 & 31 & 27 \\
\text { e. purple smooth } \times \text { purple smooth } & 0 & 0 & 36 & 11 \\
\text { f. white spiny } \times \text { white spiny } & 0 & 45 & 0 & 16
\end{array}$$

Bryan Valdivia
Bryan Valdivia
Numerade Educator
05:05

Problem 28

A pea plant heterozygous for plant height, pod shape, and flower color was selfed. The progeny consisted of 272 tall, inflated pods, purple flowers; 92 tall, inflated, white flowers; 88 tall, flat pods, purple; 93 dwarf, inflated, purple; 35 tall, flat, white; 31 dwarf, inflated, white; 29 dwarf, flat, purple; 11 dwarf, flat, white. Which alleles are dominant in this cross?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
05:02

Problem 29

In the fruit fly Drosophila melanogaster, the following genes and mutations are known:
Wing size: recessive allele for tiny wings $t ;$ dominant allele for normal wings $T$
Eye shape: recessive allele for narrow eyes $n$ dominant allele for normal (oval) eyes $N$
For each of the four following crosses, give the genotypes of each of the parents.

Syed Vasi
Syed Vasi
Numerade Educator
07:44

Problem 30

Based on the information you discovered in the previous problem, answer the following:
a. A female fruit fly with genotype $T_{l} n n$ is mated to a male of genotype $T t N n .$ What is the probability that any one of their offspring will have normal phenotypes for both characters?
b. What phenotypes would you expect among the offspring of this cross? If you obtained 200 progeny, how many of each phenotypic class would you expect?

Melissa Donough
Melissa Donough
Numerade Educator
01:49

Problem 31

Considering the yellow and green pea color phenotypes studied by Gregor Mendel:
a. What is the biochemical function of the protein that is specified by the gene responsible for the pea color phenotype?
b. $A$ null allele of a gene is an allele that does not specify any of the biochemical function that the gene normally provides. Of the two alleles $Y$ and $y$ which is more likely to be a null allele?
c. In terms of the underlying biochemistry, why is the $Y$ allele dominant to the $y$ allele?
f. The Sgr enzyme is not needed for the survival of a pea plant, but the genomes of organisms contain many so-called essential genes needed for an individual's survival. For such genes, heterozygotes for the normal allele and the null allele survive, but individuals homozygous for the null allele die soon after the male and female gametes, each with a null allele, come together at fertilization. In light of your answer to part (e), what does this fact tell you about the advantage to an organism of having two copies of their genes?
g. Do you think that a single pea pod could contain peas with different phenotypes? Explain.
h. Do you think that a pea pod could be of one color (say, green) while the peas within the pod could be of a different color (say, yellow)? Explain.
d. Why are peas that are $y y$ homozygotes green?
e. The amount of the protein specified by a gene is roughly proportional to the number of functional copies of the gene carried by a cell or individual. What do the phenotypes of $Y Y$ homozygotes, $Y y$ heterozygotes, and $y y$ homozygotes tell us about the amount of the Sgr enzyme (the product of the pea color gene) needed to produce a yellow color?

Lourence Gonhovi
Lourence Gonhovi
Numerade Educator
03:17

Problem 32

What would have been the outcome (the genotypic and phenotypic ratios ) in the $\mathrm{F}_{2}$ of Mendel's dihybrid cross shown in Fig. 2.15 if the alleles of the pea color gene $(Y, y)$ and the pea shape gene $(R, r)$ did not assort independently and instead the alleles inherited from a parent always stayed together as a unit?

Melissa Donough
Melissa Donough
Numerade Educator
04:12

Problem 33

Recall that Mendel obtained pure-breeding plants with either long or short stems and that hybrids had long stems (Fig. 2.8). Monohybrid crosses produced an $\mathrm{F}_{2}$ generation with a 3: 1 ratio of long stems to short stems, indicating that this difference in stem length is governed by a single gene. The gene that likely controlled this trait in Mendel's plants has been discovered, and it specifies an enzyme called $63 \beta \mathrm{H}$, which catalyzes the reaction shown in the accompanying figure. The product of the reaction, gibberellin, is a growth hormone that makes plants grow tall. What is the most likely hypothesis to explain the difference between the dominant allele $(L)$ and the recessive allele $(l) ?$

Melissa Donough
Melissa Donough
Numerade Educator
04:52

Problem 34

The gene that likely controlled flower color (purple or white $)$ in Mendel's pea plants has also been identified. The flower color gene specifies a protein called bHLH required by cells to make three different enzymes (DFR, ANS, and 3GT) that function in the pathway shown in the accompanying figure, leading to synthesis of the purple pigment anthocyanin.
a. What is the most likely explanation for the difference between the dominant allele ( $P$ ) and the recessive allele $(p)$ of the gene responsible for these flower colors?
b. Given the biochemical pathway shown, could a different gene have been the one governing Mendel's flower colors?

Jennifer Stoner
Jennifer Stoner
Numerade Educator
00:09

Problem 35

For each of the following human pedigrees, indicate whether the inheritance pattern is recessive or dominant. What feature(s) of the pedigree did you use to determine the mode of inheritance? Give the genotypes of affected individuals and of individuals who carry the disease allele but are not affected.

Dennis Howard
Dennis Howard
Numerade Educator
09:04

Problem 36

Consider the pedigree that follows for cutis laxa, a connective tissue disorder in which the skin hangs in loose folds.
a. Assuming that the trait is rare, what is the apparent mode of inheritance?
b. What is the probability that individual II-2 is a carrier?
c. What is the probability that individual II-3 is a carrier?
d. What is the probability that individual III-1 is affected by the disease?

Jenny Wu
Jenny Wu
Numerade Educator
06:54

Problem 37

A young couple went to see a genetic counselor because each had a sibling with cystic fibrosis. (Cystic fibrosis is a recessive disease, and neither member of the couple nor any of their four parents is affected.)
a. What is the probability that the female of this couple is a carrier?
b. What are the chances that their child will have cystic fibrosis?
c. What is the probability that their child will be a carrier of the cystic fibrosis disease allele?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
00:28

Problem 38

Huntington disease is a rare fatal, degenerative neurological disease in which individuals start to show symptoms in their 40 s. It is caused by a dominant allele. Joe, a man in his 20 s, just learned that his father has Huntington disease.
a. What is the probability that Joe will also develop the disease?
b. Joe and his new wife have been eager to start a family. What is the probability that their first child will eventually develop the disease?

Dennis Howard
Dennis Howard
Numerade Educator
00:10

Problem 39

Is the disease shown in the following pedigree caused by a dominant or a recessive allele? Why? Based on this limited pedigree, do you think the disease allele is rare or common in the population? Why?

Dennis Howard
Dennis Howard
Numerade Educator
04:46

Problem 40

Figure 2.22 shows the inheritance of Huntington disease in a family from a small village near Lake Maracaibo in Venezuela. The village was founded by a small number of immigrants, and generations of their descendants have remained concentrated in this isolated location. The allele for Huntington disease has remained unusually prevalent there.
a. Why could you not conclude definitively that the disease is the result of a dominant or a recessive allele solely by looking at this pedigree?
b. Is there any information you could glean from the family's history that might imply the disease is due to a dominant rather than a recessive allele?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
09:22

Problem 41

Consider the cystic fibrosis pedigree in Figure $2.24 \mathrm{a}$
a. Assuming that one of the individuals in generation I was a carrier, and that no one from outside the family was a carrier, what was the probability that any single child of the consanguineous couple in generation V would have cystic fibrosis? (Assume that none of their children is born yet, so you don't know that VI-4 has the disease.)
b. Assuming that one of the individuals in generation I was a carrier and that $1 / 1000$ people in the population is a carrier, and knowing that VI-4 has the disease, how likely was it that VII-1 would be affected?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
00:12

Problem 42

The common grandfather of two first cousins has hereditary hemochromatosis, a recessive condition causing an abnormal buildup of iron in the body. Neither of the cousins has the disease nor do any of their relatives.
a. If the first cousins had a child, what is the chance that the child would have hemochromatosis? Assume that the unrelated, unaffected parents of the cousins are not carriers.
b. How would your calculation change if you knew that 1 out of every 10 unaffected people in the population (including the unrelated parents of these cousins) was a carrier for hemochromatosis?

Dennis Howard
Dennis Howard
Numerade Educator
00:10

Problem 43

People with nail-patella syndrome have poorly developed or absent kneecaps and nails. Individuals with alkaptonuria have arthritis as well as urine that darkens when exposed to air. Both nail-patella syndrome and alkaptonuria are rare phenotypes. In the following pedigree, vertical red lines indicate individuals with nail-patella syndrome, while horizontal green lines denote individuals with alkaptonuria.
a. What are the most likely modes of inheritance of nail-patella syndrome and alkaptonuria? What genotypes can you ascribe to each of the individuals in the pedigree for both of these phenotypes?
b. In a mating between IV-2 and IV-5, what is the chance that the child produced would have both nail-patella syndrome and alkaptonuria? Nailpatella syndrome alone? Alkaptonuria alone? Neither defect?

Dennis Howard
Dennis Howard
Numerade Educator
02:13

Problem 44

Midphalangeal hair (hair on top of the middle segment of the fingers) is a common phenotype caused by a dominant allele $M .$ Homozygotes for the recessive allele ( $m$ ) lack hair on the middle segment of their fingers. Among 1000 families in which both parents had midphalangeal hair, 1853 children showed the trait while 209 children did not. Explain this result.

KS
Katelyn Surette
Numerade Educator
09:52

Problem 45

A man with Huntington disease (he is heterozygous
$\left.H D H D^{+}\right)$ and a normal woman have two children.
a. What is the probability that only the second child has the disease?
b. What is the probability that only one of the children has the disease?
c. What is the probability that none of the children has the disease?
d. Answer (a) through
(c) assuming that the couple had 10 children.
e. What is the probability that 4 of the 10 children in the family in (d) have the disease?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
02:08

Problem 46

Explain why disease alleles for cystic fibrosis $(C F)$ are recessive to the normal alleles $\left(C F^{+}\right),$ yet the disease alleles responsible for Huntington disease $(H D)$ are dominant to the normal alleles $\left(H D^{+}\right)$.

Marisa A
Marisa A
Numerade Educator
08:23

Problem 47

The following pedigree shows the inheritance of red hair in a family in Scotland. Red hair is caused by homozygosity for a recessive allele of a gene called MCIR. Although worldwide red hair is the rarest of human hair colors, red hair is not uncommon in Scotland. In fact, $40 \%$ of Scots without red hair are nonetheless carriers of the red hair allele.
a. Why does red hair show a horizontal inheritance pattern in this particular pedigree even though the trait is caused by a recessive allele?
b. Assuming that individual III-2 has a child with the Scottish woman shown (III-1) who is not a close relative, what is the probability that this child (IV-1) will have red hair?
c. What is the probability that the child of first cousins III-9 and III-10 (IV-2), will have red hair?

Bryan Valdivia
Bryan Valdivia
Numerade Educator