Human Heredity: Principles and Issues (MindTap Course List)
11th Edition
ISBN: 9781305251052
Author: Michael Cummings
Publisher: Cengage Learning
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Chapter 10, Problem 2CS
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
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.
Should the parents be concerned about the heterozygous condition as well as the homozygous mutant condition?
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Achondroplasia is an autosomal dominant disorder characterized by disproportionate short stature: the legs and arms of people with achondroplasia are short compared with the head and trunk. The disorder is due to a base substitution in the gene, located on the short arm of chromosome 4, that encodes fibroblast growth factor receptor 3 (FGFR3). Although achondroplasia is clearly inherited as an autosomal dominant trait, more than 80% of the people who have achondroplasia are born to parents with normal stature. This high percentage indicates that most cases are caused by newly arising mutations; these cases (not inherited from an affected parent) are referred to as sporadic. Studies have demonstrated that sporadic cases of achondroplasia are almost always caused by mutations inherited from the father (paternal mutations). In addition, the occurrence of achondroplasia is higher among the children of older fathers; approximately 50% of children with achondroplasia are born to fathers…
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Chapter 10 Solutions
Human Heredity: Principles and Issues (MindTap Course List)
Ch. 10.4 - Prob. 1GRCh. 10.4 - Prob. 2GRCh. 10.7 - Prob. 1EGCh. 10.7 - Prob. 2EGCh. 10 - A couple was referred for genetic counseling...Ch. 10 - A couple was referred for genetic counseling...Ch. 10 - A couple was referred for genetic counseling...Ch. 10 - Many individuals with metabolic diseases are...Ch. 10 - Prob. 2QPCh. 10 - Enzymes have all the following characteristics...
Ch. 10 - Questions 4 through 6 refer to the following...Ch. 10 - Questions 4 through 6 refer to the following...Ch. 10 - Prob. 6QPCh. 10 - Prob. 7QPCh. 10 - Prob. 8QPCh. 10 - a. Compounds A, B, C, and D are known to be...Ch. 10 - b. Compounds A, B, C, and D are known to be...Ch. 10 - a. If an individual who is homozygous for the...Ch. 10 - Prob. 12QPCh. 10 - Suppose that in the formation of phenylalanine...Ch. 10 - If phenylalanine was not an essential amino acid,...Ch. 10 - Phenylketonuria and alkaptonuria are both...Ch. 10 - The normal enzyme required for converting sugars...Ch. 10 - Knowing that individuals who are homozygous for...Ch. 10 - Prob. 18QPCh. 10 - A person was found to have very low levels of...Ch. 10 - If an extra nucleotide is inserted in the first...Ch. 10 - Transcriptional regulators are proteins that bind...Ch. 10 - Prob. 22QPCh. 10 - Prob. 23QP
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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 if the couple wanted prenatal testing so that a normal fetus could be aborted?arrow_forwardClara has polydactyly, an autosomal dominant that is 80% penetrant. Clara inherited her polydactyly from her mother, her father had no polydactyly in his family. She has an extra toe on her left foot. Her husband Ralph has no polydactyly in his family. A) What is the chance that Clara will have a child that will inherit polydactyly? B) What is the chance that the child will express polydactyly. You can leave these as un-calculated equations.arrow_forwardSheree is referred to a genetic counselor because a cystic fibrosis (CF) test done as a routine part of her prenatal care indicated that she is a carrier of the most common mutant allele. Sheree is stunned, because no one in her family has the disease. She is 26 years old. The genetic counselor would most likely explain autosomal recessive inheritance and suggest that Sheree's husband be tested for the CF allele. explain autosomal dominant inheritance and suggest that Sheree's husband be tested for the CF allele. explain autosomal recessive inheritance and suggest that Sheree's parents be tested for the CF allele. advise Sheree to have amniocentesis to check the fetus for the CF genotype.arrow_forward
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