Essentials of Genetics (9th Edition) - Standalone book
9th Edition
ISBN: 9780134047799
Author: William S. Klug, Michael R. Cummings, Charlotte A. Spencer, Michael A. Palladino
Publisher: PEARSON
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Chapter 21, Problem 3CS
CASE STUDY|A genetic flip of the coin
On July 11, 2008, twin sons were born to Stephan Gerth from Germany and AddoGerth from Ghana. Stephan is very fair-skinned with blue eyes and straight hair; Addo is dark-skinned, with brown eyes and curly hair. The first born of the twins, Ryan, is fair-skinned, with blue eyes and straight hair; his brother, Leo, has light brown skin, brown eyes, and curly hair. Although the twins' hair texture and eye color were the same as those of one or the other parent, the twins had different skin colors, intermediate to that of their parents. Experts explained that the blending effect of skin color in the twins resulted from quantitative inheritance involving at least three different gene pairs, whereas hair texture and eye color are not quantitatively inherited. Using thisas an example of quantitative genetics, we can ask the following questions:
Would twins showing some parental traits (hair texture, eye color) but a blending of other traits (skin color in this case) seem to be a commonplace event, or are we looking at a “one in a million” event?
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You are a genetic counselor. How would you advise a couple who wants to know their chances of having a baby with Duchenne-muscular dystrophy. Hannah is not a carrier, but her husband Barry has a brother, James, who died from the disease. Duchenne-muscular dystrophy is an x-linked condition, the allele responsible is recessive and people who have the disease die in childhood.
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In man, two abnormal conditions, cataracts (C) in the eyes and excessive fragility (F) in the bones, seem
to depend on separate dominant genes located on different chromosomes. Normal vision and normal
bones are recessive traits. A man with cataracts and nomal bones, whose father had normal eyes, married
a woman free from cataracts but with fragile bones. Her father had normal bones.
11.
What is the genotype of the man with cataracts and nomal bones?
What is the genotype of the woman with normal vision and fragile bones?
What type of offspring might this couple expect?
Genotypes Phenotypes
What is the probability that their first child will,
(a) be free from both abnormalities
(b) have cataracts but not fragile bones
(c) have fragile bones but not cataracts
(d) have both cataracts and fragile bones?
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Chapter 21 Solutions
Essentials of Genetics (9th Edition) - Standalone book
Ch. 21 -
CASE STUDY | A genetic flip of the coin
On July...Ch. 21 - CASE STUDY|A genetic flip of the coin On July 11,...Ch. 21 -
CASE STUDY|A genetic flip of the coin
On July...Ch. 21 - HOW DO WE KNOW?
1. In this chapter, we focused on...Ch. 21 - Review the Chapter Concepts list on page 422....Ch. 21 -
3. Define the following: (a) polygenic, (b)...Ch. 21 - A dark-red strain and a white strain of wheat are...Ch. 21 - Height in humans depends on the additive action of...Ch. 21 -
6. An inbred strain of plants has a mean height...Ch. 21 - Prob. 7PDQ
Ch. 21 - In the following table, average differences of...Ch. 21 - What kind of heritability estimates (broad sense...Ch. 21 - List as many human traits as you can that are...Ch. 21 - Corn plants from a test plot are measured, and the...Ch. 21 -
12. The following variances were calculated for...Ch. 21 - The mean and variance of plant height of two...Ch. 21 - A hypothetical study investigated the vitamin A...Ch. 21 - In a herd of dairy cows the narrow-sense...Ch. 21 - In an assessment of learning in Drosophila, flies...Ch. 21 - Suppose you want to develop a population of...Ch. 21 -
18. In a population of tomato plants, mean fruit...Ch. 21 - In a population of 100 inbred, genotypically...Ch. 21 - In a cross between a strain of large guinea pigs...Ch. 21 - While most quantitative traits display continuous...
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- In human beings, the gene for red‑green colorblindness (r) is sex‑linked and recessive to its allele for normal vision (R), while the gene for freckles (F) is autosomal and dominant over its allele for nonfreckled (f). A nonfreckled, normal‑visioned woman whose father was freckled and colorblind, marries a freckled, colorblind man whose mother was nonfreckled. What is the genotype of the woman's father? What is the probability that the couple's first child will be a non-freckled, normal visioned girl? What is the probability that the first two children born to the couple will be freckled and colorblind girls?arrow_forwardIn human beings, the gene for red‑green colorblindness (r) is sex‑linked and recessive to its allele for normal vision (R), while the gene for freckles (F) is autosomal and dominant over its allele for nonfreckled (f). A nonfreckled, normal‑visioned woman whose father was freckled and colorblind, marries a freckled, colorblind man whose mother was nonfreckled. What is the probability that the first child born to the couple will either be a freckled, colorblind boy or a non‑freckled, normal visioned girl or a non-freckled, normal visioned boy? What is the probability that the first four children born to the couple will be freckled and normal visioned girls?arrow_forwardDuchenne muscular dystrophy is an X-linked, recessive disorder in which muscles waste away early in life, resulting in death in the teens or twenties. A man and woman in their late thirties have five children—three boys (ages 1, 3, and 10 years) and two girls (ages 5 and 7 years). The oldest, boy shows symptoms of the disease. What are the probabilities that their other children will develop the disease? Give only typing answer with explanation and conclusionarrow_forward
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The counsellor briefly reviewed the phenotypic features of individuals with achondroplasia. These include facial features (large head with prominent forehead; small, flat nasal bridge; and prominent jaw), very short stature, and shortening of the arms and legs. Physical examination and skeletal X-ray films are used to diagnose this condition. Final adult height is approximately 4 feet. Because achondroplasia is an autosomal dominant condition, a heterozygote has a 1-in-2, or 50%, chance of passing this trait to his or her offspring. However, about 75% of those with achondroplasia have parents of average size who do not carry the mutant allele. In these cases, achondroplasia is due to a new mutation. In the couple being counseled, each individual is heterozygous, and they are at risk for having a homozygous child with two copies of the mutated gene. Infants with homozygous achondroplasia are either stillborn or die shortly after birth. 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- A couple was referred for genetic counseling because they wanted to know the chances of having a child with dwarfism. Both the man and the woman had achondroplasia (MIM 100800), the most common form of short-limbed dwarfism. The couple knew that this condition is inherited as an autosomal dominant trait, but they were unsure what kind of physical manifestations a child would have if it inherited both mutant alleles. They were each heterozygous for the FGFR3 (MIM 134934) allele that causes achondroplasia. Normally, the protein encoded by this gene interacts with growth factors outside the cell and receives signals that control growth and development. In achrodroplasia, a mutation alters the activity of the receptor, resulting in a characteristic form of dwarfism. Because both the normal and mutant forms of the FGFR3 protein act before birth, no treatment for achrondroplasia is available. The parents each carry one normal allele and one mutant allele of FGRF3, and they wanted information on their chances of having a homozygous child. The counsellor briefly reviewed the phenotypic features of individuals with achondroplasia. These include facial features (large head with prominent forehead; small, flat nasal bridge; and prominent jaw), very short stature, and shortening of the arms and legs. Physical examination and skeletal X-ray films are used to diagnose this condition. Final adult height is approximately 4 feet. Because achondroplasia is an autosomal dominant condition, a heterozygote has a 1-in-2, or 50%, chance of passing this trait to his or her offspring. However, about 75% of those with achondroplasia have parents of average size who do not carry the mutant allele. In these cases, achondroplasia is due to a new mutation. In the couple being counseled, each individual is heterozygous, and they are at risk for having a homozygous child with two copies of the mutated gene. Infants with homozygous achondroplasia are either stillborn or die shortly after birth. The counselor recommended prenatal diagnosis via ultrasounds at various stages of development. In addition, a DNA test is available to detect the homozygous condition prenatally. What is the chance that this couple will have a child with two copies of the dominant mutant gene? What is the chance that the child will have normal height?arrow_forwardProblem) A university student is studying the inheritance of 2 genes of pea plants. Color of plant: Blue is dominant (B), and yellow is recessive (b) Spikes or no spikes: Having spikes is dominant (G), and having no spikes is recessive (g). Which of the following findings would indicate to the student that these two traits are located close together on the same chromosome? a) The traits show independent assortment b) All gametes of a double heterozygous individual (BbGg) are either BG or bg c) A double heterozygous individual has four types of gametes in approximately equal proportions: BG, Bg, bG, and bg d) Student finds that there is frequent crossing over between the 2lociarrow_forwardNormal wife Affected husband As a genetic counsellor you are presented with a married couple where one of them has a family history of this disease. The husband is affected by this disease and the wife is normal. The couple, who are thinking of starting a family, would like to know what their chances are of having a child born with this condition. They would also like to know what the probabilities are of having an affected boy or affected girl. Use the symbols above to complete the diagram right and determine the probabilities stated below (expressed as a proportion or percentage). Parents 4. Determine the probability of having: Gametes (a) Affected children: Possible (b) An affected girl: fertilizations (c) An affected boy: O O O O Children Affected aite if 耳arrow_forward
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