Which of the following is a characteristic of an x-linked recessive disorder pedigree?
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Choose your answers from a-d by clicking the radio button next to each choice and then press 'Submit' to get your score. Question 1Neurofibromatosis type 1 is one of the most common autosomal dominant disorders. A woman with neurofibromatosis type 1 has an unaffected partner. Which of the following is correct regarding their children? a) The probability that each of their children will be affected is 1 in 4. b) The probability that their second child will be affected if their first child is affected is 1 in 4. c) The probability that their third child will be affected if their first two children are affected is 1 in 2. d) If their first child is affected then their second child will not be affected. Question 2Retinoblastoma usually occurs as a sporadic event but in around 10% of cases there is a positive family history due to autosomal dominant inheritance. In these families the penetrance is approximately 80% (= 0.8). A woman with retinoblastoma, whose father and grandfather were also affected, has an unaffected partner with no relevant family history. Which of the following is correct regarding their children? a) The probability that their first child will be affected is 0.25. b) The probability that their first child will be affected is 0.4. c) The probability that each of their children will be affected is 0.5. d) The probability that each of their children will be affected is 0.4 X 0.5. Question 3Achondroplasia shows autosomal dominant inheritance with complete penetrance. A man with achondroplasia has an unaffected partner of normal height. Their first two children are not affected. Which of the following is correct? a) The probability that their next child will be affected is 1 in 2. b) The probability that each of their children will be affected is less than 1 in 2 because the parents of the man with achondroplasia are not affected. c) The mother of these children has a sister with achondroplasia. This increases the risk that the children could be carriers. d) If their third child is unaffected, then the probability that their fourth child will be affected is 1 in 8. Question 4Tay-Sachs disease shows autosomal recessive inheritance. Parents of a newly diagnosed affected child are referred for genetic counseling. It would be correct to tell them that: a) the probability that their next child will be affected is 1 in 2. b) the probability that the older unaffected sister of the affected child is a carrier is 1 in 2. c) the fact that their last child was affected means that their next three children will not be affected. d) the probability that each parent is a carrier is 1. Question 5Phenylketonuria shows autosomal recessive inheritance with an incidence of 1 in 10 000. Assume that the population is in Hardy-Weinberg equilibrium. Which of the following is correct? a) The frequency of the mutant allele is 1 in 1000. b) The frequency of the normal (wild-type) allele is 49/50. c) The carrier frequency is 1 in 100. d) The carrier frequency is approximately 1 in 50. Question 6A young man with phenylketonuria, who was successfully treated following diagnosis on newborn screening, is planning to start a family with his healthy, unaffected, and unrelated partner, who has no family history of phenylketonuria . Phenylketonuria shows autosomal recessive inheritance with an incidence of 1 in 10 000. Assume that the population is in Hardy-Weinberg equilibrium. Which of the following is correct? a) The probability that his partner is a carrier is 1 in 100. b) The probability that the man will transmit a mutant allele to his first child is 1 in 2. c) The probability that his partner will transmit a mutant allele to their first child is 1 in 50. d) The probability that their first child will be affected is 1 in 100. Question 7Cystic fibrosis shows autosomal recessive inheritance with an incidence of 1 in 2500. The unaffected brother of an affected girl is referred for genetic counseling. Assume that the population is in Hardy-Weinberg equilibrium. Which of the following is correct? a) The probability that the brother is a carrier is 1/2. b) If the brother has a child with a healthy unrelated partner the probability that the child will be affected is 1 in 150. c) If the brother has a child with his first cousin the probability that the child will be affected is 1 in 12. d) If the affected sister has a child with her first cousin the probability that the child will be affected is 1 in 4. Question 8Hunter syndrome is a rare form of mucopolysacchararidosis that differs from all other forms in that it shows X-linked recessive inheritance. A woman with two affected brothers is referred for genetic counseling. Which of the following is correct? a) The probability that she is a carrier is 2/3. b) If she is a carrier then the probability that each of her sons will be affected is 1 in 4. c) If she is a carrier then the probability that each of her daughters will be a carrier is 1 in 4. d) Before any carrier testing is carried out the woman can be correctly informed that the probability that her first son will be affected is 1 in 4. Question 9Haemophilia A is a severe coagulation disorder that shows X-linked recessive inheritance. Red-green colour blindness also shows X-linked recessive inheritance. A man with both haemophilia A and colour blindness is referred for genetic counseling. Assume that his partner is not a carrier of either of these conditions. Which of the following is correct? a) The probability that each of his daughters will be a carrier of haemophilia A is 1 in 2. b) The probability that each of his daughters will be a carrier of colour blindness is 1 in 2. c) The probability that each of his daughters will be a carrier of both conditions is 1. d) The probability that each of his sons will be affected with haemophilia A is 1 in 2. Question 10A woman who has two brothers and a maternal uncle (her mother's brother) with non-specific X-linked mental retardation is referred for genetic counseling. There are no diagnostic tests available to help determine whether or not she is a carrier. Which of the following is correct? a) The prior probability that she is a carrier is 1 in 4. b) The woman already has two unaffected sons. Therefore the probability that she is a carrier can be calculated using Bayes' theorem to be 1 in 5. c) This means that the probability that her next son will be affected or that her next daughter will be a carrier is 1 in 5. d) The probability that the maternal grandmother of this woman is a carrier is 1 in 2. Question 11In this pedigree A and B represent alleles at a marker locus closely linked to the disease locus. Affected individuals are shown as shaded. The disease status in III 1 is unknown. Which of the following is correct? a) The probable pattern of inheritance shown by the disease in this family is autosomal recessive. b) If recombination does not occur the probability that III 1 will be affected if she has an AB marker genotype is 1. c) If recombination does not occur, the probability that III 1 will be affected if she has a BB marker genotype is 1. d) If the recombination fraction between the disease and marker loci equals 0.04, the probability that III 1 will be affected if she inherits an AB marker genotype equals 0.96. Question 12In this pedigree II 1 is affected with an autosomal recessive disorder. The disease status for II 2 and II 3 is unknown. A and B represent alleles at a locus which is tightly linked to the disease locus with recombination fraction of 0. On the basis of the linked marker genotypes II 2 can be told that: a) he is affected. b) he is a carrier. c) he is homozygous unaffected. d) the marker results are not informative. Question 13On the basis of the linked marker genotypes II 3 can be told that: a) she is affected. b) she is a carrier. c) she is homozygous unaffected. d) the marker results are not informative. Question 14In this pedigree II 1 is affected with an autosomal recessive disorder. The disease status for II 2, II 3 and II 4 is unknown. A and B represent alleles at a locus which is tightly linked to the disease locus with recombination fraction of 0. On the basis of the linked markers II 2 can be told that: a) he is affected. b) he is a carrier. c) he is homozygous unaffected. d) the marker results are not informative. Question 15In the pedigree shown in Question 14, on the basis of the linked marker results II 3 can be told that: a) she is affected. b) she is a carrier. c) she is homozygous unaffected. d) the marker results are not informative. Question 16In the pedigree shown in question 14, on the basis of the linked marker results II 4 can be told that: a) she is affected. b) she is a carrier. c) she is homozygous unaffected. d) the marker results are not informative. Question 17In this pedigree II 1 is affected with an autosomal recessive disorder. The disease status for II 2 is unknown. A and B represent alleles at a locus which is tightly linked to the disease locus with recombination fraction of 0. Using the linked markers, II2 can be told that: a) she is affected. b) she is a carrier. c) she is homozygous unaffected. d) the marker results are not informative. Question 18In this pedigree II 3 and III 1 are affected with an X-linked recessive disorder which is tightly linked to a marker locus with alleles A and B, with a recombination fraction of 0 between the disease and marker loci. a) Marker A. b) Marker B. c) neither A nor B. d) The results are not informative. Question 19The marker genotype for I 2 must have been: a) AA b) AB c) BB d) The results are not informative Question 20Using the linked markers III 3 can be told that: a) she is affected. b) she is a carrier. c) she is not a carrier. d) The results are not informative. Question 21In this pedigree I 1 and II 2 have Becker muscular dystrophy which shows X-linked recessive inheritance. III 2 has oculocutaneous albinism which shows autosomal recessive inheritance with an incidence in the general population of 1 in 10 000. The disease status for both Becker muscular dystrophy and oculocutaneous albinism is unknown for IV 1 and IV 2. a) 1/4 b) 2/3 c) 1/2 d) 1 Question 22What is the probability that III 3 is a carrier of oculocutaneous albinism? a) 1/4 b) 2/3 c) 1/2 d) 1 Question 23What is the probability that IV 1 is a carrier of oculocutaneous albinism? a) 1/4 b) 1/2 c) 2/3 d) 99/100 Question 24What is the probability that IV 2 will be affected with Becker muscular dystrophy? a) 1/4 b) 1/2 c) 0 d) 1 Question 25What is the probability that IV 2 will be affected with oculocutaneous albinism? a) 1/100 b) 1/50 c) 1/24 d) 1/12
About the bookFind out more, read a sample chapter, or order an inspection copy if you are a lecturer, from the Higher Education website What is XX-linked recessive inheritance refers to genetic conditions associated with mutations in genes on the X chromosome. A male carrying such a mutation will be affected, because he carries only one X chromosome. A female carrying a mutation in one gene, with a normal gene on the other X chromosome, is generally unaffected.
Which of the following is an XDuchenne muscular dystrophy, some types of colorblindness and hemophilia A are examples of X-linked recessive disorders.
What are the characteristics of a recessive pedigree?The following represent the characteristics of an autosomal recessive trait: The trait often affects a group of siblings. However, that particular trait is not present in their parents (predecessors) or progeny (future generation). The proportion of males and females affected by the trait is the same in the population.
Which of the following are the characteristics of XIn X-linked recessive inheritance, a daughter inherits a single mutated gene on the X chromosome from one of her parents. The X chromosome she inherits from the other parent will usually cancel the effect of the mutation, and she most likely will not have the genetic condition.
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