Concept explainers
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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Human Heredity: Principles and Issues (MindTap Course List)
- 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_forwardTuberous Sclerosis (TS) is an autosomal dominant genetic disease characterized by seizures, mental retardation, autism, and benign tumors of the brain, heart, skin, and kidneys. The kidney tumors can also be malignant. This disease exhibits a wide range of severity, and only about 1/3 of the cases are inherited. Two different genes have been tightly linked to the disease in families where it is inherited. The remaining 2/3 appear to be due to mutations in one of the 2 genes as well. Overall it appears that 1/2 are caused by mutations in TSC1 and the other half by mutations in TSC2. A rat model for hereditary renal carcinoma (kidney cancer) has been found. Southern and Northern blot analysis of the TSC1 and TSC2 gene revealed no differences between these rats and normal rats. Not all the rats in the strain would get cancer but a significant proportion did and those were selected for and used in experiments. 1. a) What was detected by the Southern blots? (look this up, make your…arrow_forwardCystic fibrosis (CF) is an autosomal recessive condition triggered by the overproduction of sticky mucus that clogs the lungs and pancreas. It is a life-threatening disease, but medical advances helped the afflicted to live through adulthood. The mother of Claudia died from cystic fibrosis, but her father was normal and never had any relative with CF. Her fiancé, Marcus, turned out to be a carrier of the CF allele. What are the genotypes of Claudia and Marcus? Claudia: ________________________ Marcus: _____________________ They planned to have four children. What is the probability that: a. all children will be normal b. at least two will be normal PLEASE SHOW COMPLETE SOLUTIONarrow_forward
- Cystic Fibrosis (CF) is an autosomal recessive condition. Therefore, heterozygous (Cc) carriers do not display symptoms. Two parents who are carriers plan to start a family and you are a genetic counselor helping to advise them about their chances of having children affected by CF. a) Suppose the couple has 4 children, each one year apart. What is the probability that all 4 children will inherit CF? b) What is the probability that any 3 of their 4 children will not inherit CF, but 1 will be affected? c) What is the probability that their first child will not inherit CF, but the younger 3 children will inherit CF?arrow_forwardBelow is a pedigree chart for a family that has a history of Alkaptonuria. Individuals infected with this condition can have darkened skin, brown urine, and can suffer from joint damage and other complications. Given this pedigree answer the following questions. Given the data in the pedigree chart is this genetic condition autosomal dominant or autosomal recessive? What are the genotypes for #1, #2, and #3? If either of the 4th generation "aa" females were to mate with a homozygous dominant male would any of their offspring illustrate the phenotype? Why or why not?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
- Albinism, lack of pigmentation in humans, results from an autosomal recessive gene designated a. Two parents with normal pigmentation have an albino child. What is the probability that their next child will be albino? What is the probability that the next child will be an albino girl? If the child is normal, what is the probability that it will be a carrier (heterozygous) for the albino gene?arrow_forwardA woman knows that her mother is a carrier of Kartagener’s syndrome (an autosomal recessive disorder). The woman does not know if either she or her husband are carriers. The couple wants to have a child, but is worried about whether or not they could have a child with Kartagener’s syndrome. Should the couple seek the advice of a genetic counselor? In other words, is there a chance they could have an affected child? If there is a chance, please make sure your answer includes the specific parental genotypes necessary to make this possible.arrow_forwardThe following pedigree illustrates the inheritance of Nance–Horan syndrome, a rare genetic condition in which affected people have cataracts and abnormally shaped teeth.arrow_forward
- A young couple went to see a genetic counselor because each had a sibling affected 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 be affected with cystic fibrosis? c. What is the probability that their child will be a carrier of the cystic fibrosis mutation?arrow_forwardMrs. Dee (40 years old) and her husband have an amniocentesis for advanced maternal age. They already have four healthy children. They receive results indicating a 47,XXY karyotype. What is the phenotypic sex of the fetus? How many Barr bodies will be found in each somatic cell?arrow_forwardThe attached image is a pedigree of a family with a history of sickle cell anemia (the individuals with the filled-in symbols have the disease and no new mutations are occurring in any individual). Sickle cell anemia is inherited in an autosomal recessive manner. What is the probability that the individual with the question mark (?) will get the disease? a) 1/4 b) 1/2 c) 2/3 d) 1arrow_forward
- Human Heredity: Principles and Issues (MindTap Co...BiologyISBN:9781305251052Author:Michael CummingsPublisher:Cengage Learning