Concept explainers
Over a period of several years, a large hospital kept track of the number of births of babies displaying the trait achondroplasia. Achondroplasia is a very rare autosomal dominant condition resulting in dwarfism with abnormal body proportions. After 120,000 births, it was noted that 27 babies had been born with achondroplasia. One physician was interested in determining how many of these dwarf babies resulted from new mutations and whether the apparent mutation rate in this geographical area was higher than normal. He looked up the families of the 27 dwarf births and discovered that four of the dwarf babies had a dwarf parent. What is the apparent mutation rate of the achondroplasia gene in this population? Is it unusually high or low?
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Genetics: From Genes to Genomes
- The Figueroa family has a genetically inherited trait called ocular albinism—lack of pigment in the eye—which is caused by a 516-bp deletion in an exon of a single gene. DNA for this gene was amplified from each member of the family and run on the gel shown below. The thickness of the band indicates the relative amount of DNA. Use the pedigree and the gel to determine the most likely mode of inheritance for this disease. a) x-linked dominant b)x-linked recessive c)autosomal dominant d) autosomal recessive e) cant be determinedarrow_forwardSix months pregnant, an expectant mother had a routine ultrasound that showed that the limbs of the fetus were unusually short. Her physician suspected that the baby might have a genetic form of dwarfism called achondroplasia, an autosomal dominant trait occurring with a frequency of about 1 in 27,000 births. The parents were directed to a genetic counselor to discuss this diagnosis. In the conference, they learned that achondroplasia is caused by a mutant allele. Sometimes it is passed from one generation to another, but in 80 percent of all cases it is the result of a spontaneous mutation that arises in a gamete of one of the parents. They also learned that most children with achondroplasia have normal intelligence and a normal life span. 1. What information would be most relevant to concluding which of the two mutation origins, inherited or new, most likely pertains in this case? How does this conclusion impact on this couple’s decision to have more children? 2. It has been…arrow_forwardA scientist investigating the genome of two related individuals observes a difference of a few nucleotides in one individual compared to the other. The nucleotide differences are in a region of noncoding DNA on chromosome 1. Would these differences be considered a mutation? Why or why not? Yes, the difference in nucleotide sequences between the individuals is a mutation because it will affect the phenotype of the two individuals. Yes, any heritable variation in the nucleotide sequence is considered a mutation, even if that variation is in a noncoding region of DNA. Not enough information was provided to determine if this nucleotide difference is a mutation because the effect on phenotype is unknown. No, the change in nucleotide sequence doesn't appear in a coding region of the DNA and so can't be a mutation.arrow_forward
- Diamond–Blackfan anemia (DBA) is a rare, dominantgenetic disorder characterized by bone marrow malfunction,birth defects, and a predisposition to certaincancers. Infants with DBA usually develop anemia in the firstyear of life, have lower than normal production of red blood cellsin their bone marrow, and have a high risk of developing leukemiaand bone cancer. At the molecular level, DBA is causedby mutations in any one of 10 genes that encode ribosomalproteins. The first-line therapy for DBA is steroid treatment,but more than half of affected children develop resistance tothe drugs and in these cases, treatment is halted. DBA can betreated successfully with bone marrow or stem cell transplantsfrom donors with closely matching immune system markers.Transplants from unrelated donors have significant levels ofcomplications and mortality. Given that a faulty ribosomal protein is the culprit and causesDBA, discuss the possible role of normal ribosomal proteins.Why might bone marrow cells be…arrow_forwardDiamond–Blackfan anemia (DBA) is a rare, dominantgenetic disorder characterized by bone marrow malfunction,birth defects, and a predisposition to certaincancers. Infants with DBA usually develop anemia in the firstyear of life, have lower than normal production of red blood cellsin their bone marrow, and have a high risk of developing leukemiaand bone cancer. At the molecular level, DBA is causedby mutations in any one of 10 genes that encode ribosomalproteins. The first-line therapy for DBA is steroid treatment,but more than half of affected children develop resistance tothe drugs and in these cases, treatment is halted. DBA can betreated successfully with bone marrow or stem cell transplantsfrom donors with closely matching immune system markers.Transplants from unrelated donors have significant levels ofcomplications and mortality. While a stem cell transplant from an unaffected donor is currentlythe only cure for DBA, genome-editing technologies mayone day enable the correction of…arrow_forwardLeber Congenital Amaurosis (LCA) causes progressive vision loss due to defects in the gene that encodes RPE65 isomerase. Affected individuals are homozygous recessive for mutant alleles of the RPE65 gene. You are trying to determine the molecular nature of the mutations in three individuals with LCA. For ease of analysis, you may assume that each individual is homozygous for the same mutant allele (though the three individuals have different mutations than each other). You use the polymerase chain reaction to amplify DNA from each patient and you determine the sequence of the DNA and compare it to unaffected individuals. You identify the following differences. Note that the non-template strand of DNA is given and the changes are highlighted using red boldface. You can assume that the sequences are in the first reading frame (eg. the first three nucleotides of each sequence is a codon). The coding region of the gene is 1602 bp and the position of the sequences shown below is…arrow_forward
- Is it possible for a severe mutation-causing hereditary condition to pass down from generation to generation without creating symptoms? Explain.arrow_forwardOver a period of several years, a large hospital kepttrack of the number of births of babies displaying thetrait achondroplasia. Achondroplasia is a very rareautosomal dominant condition resulting in dwarfismwith abnormal body proportions. After 120,000births, it was noted that 27 babies had been born withachondroplasia. One physician was interested in determining how many of these dwarf babies resultedfrom new mutations and whether the apparent mutation rate in this geographical area was higher thannormal. He looked up the families of the 27 dwarfbirths and discovered that four of the dwarf babieshad a dwarf parent. What is the apparent mutationrate of the achondroplasia gene in this population? Isit unusually high or low?arrow_forwardThe Figueroa family has a genetically inherited trait called ocular albinism-lack of pigment in the eye-which is caused by a 516-bp deletion in an exon of a single gene. DNA for this gene was amplified from each member of the family and run on the gel shown below. The thickness of the band indicates relative amount of DNA. Use the pedigree and the gel to determine the most likely mode of inheritance for this disease. Becky Ben Jasper Lyla Sam Autosomal dominant Cannot be determined Autosomal recessive X-linked dominant X-linked recessive Becky Jasper Lyla Ben Samarrow_forward
- Researchers have identified a gene in humans that (when mutated) causes tremors and unstable walking due to neurological problems. This disorder is inherited in an autosomal recessive manner, and the mutant allele isknown to result from a loss-of-function mutation. The same gene hasbeen found in mice, although a mutant mouse version has not beendiscovered. To develop an effective drug therapy to treat this disorderin humans, it would be experimentally useful to have a mouse model.In other words, it would be desirable to develop a strain of mice thatcarry the mutant allele in the homozygous condition. How would youdevelop such a strain?arrow_forwardSynpolydactyly is an abnormality characterized by webbing between partially or completely duplicated fingers or toes (Figure 18.15). The same mutations that cause the human phenotype give rise to a similar phenotype in mice. In what family of genes do you think these mutations occur?arrow_forwardAs discussed, the overall rate of mutations in humans is estimated to be about 1 × 10−8 mutations per base pair per generation. How many new mutations would you expect each person to carry, on average, based on this mutation rate? Other studies have estimated that each person carries about 100 new loss-of-function mutations. How does this number compare with your estimate of the number of mutations based on the mutation rate? What might account for any differences?arrow_forward
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