Concept explainers
A form of dwarfism known as Ellis–van Creveld syndrome was first discovered in the late 1930s, when Richard Ellis and Simon van Creveld shared a train compartment on the way to a pediatrics meeting. In the course of conversation, they discovered that they each had a patient with this syndrome. They published a description of the syndrome in 1940. Affected individuals have a short-limbed form of dwarfism and often have defects of the lips and teeth, and polydactyly (extra fingers). The largest pedigree for the condition was reported in an Old Order Amish population in eastern Pennsylvania by Victor McKusick and his colleagues (1964). In that community, about 5 per 1000 births are affected, and in the population of 8000, the observed frequency is 2 per 1000. All affected individuals have unaffected parents, and all affected cases can trace their ancestry to Samuel King and his wife, who arrived in the area in 1774. It is known that neither King nor his wife was affected with the disorder. There are no cases of the disorder in other Amish communities, such as those in Ohio or Indiana.
- (a) From the information provided, derive the most likely mode of inheritance of this disorder. Using the Hardy-Weinberg law, calculate the frequency of the mutant allele in the population and the frequency of heterozygotes, assuming Hardy— Weinberg conditions.
- (b) What is the most likely explanation for the high frequency of the disorder in the Pennsylvania Amish community and its absence in other Amish communities?
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EBK CONCEPTS OF GENETICS
- Niemann Pick Type C disease is a recessive disorder that causes the accumulation of cholesterol and other lipids in lysosomes, ultimately affecting both the liver and the nervous system. Below are the genotypes and phenotypes of offspring of a family with a history of Niemann Pick. 7 NN ( all normal phenotype) 3 Nn (all normal phenotype) 4 nn (1 early onset dementia, 1 mid-life onset dementia, 2 late-onset dementia). From this information, Niemann-Pick disease is an example of: A) variable expressivity B) incomplete dominance C) incomplete penetrance D) variable expressivity and incomplete penetrance E) multiple allelesarrow_forwardA 16-year-old girl appealed to the genetic consultation. She complains about menstruation absence. She has body disproportion: wide shoulders, narrow pelvis, shortened low extremities, aliform skin folds on the neck, ovaries underdevelopment. There is no mental deficiency. The provisional diagnosis is Turner's syndrome. What genetic method can confirm this diagnosis?arrow_forwardIn man, muscular dystrophy is a condition in which the muscles waste away during early life and may result in a shorter life expectancy. It is due to a sex-linked, recessive gene. A certain couple has five children – three boys (ages 1yr, 3yrs, and 10yrs old) and two girls (ages 5yrs and 7yrs old). The oldest boy shows the symptoms of this disease. You are their family physician and they come to you for advice. What would you tell them about the chances of their other children developing the disease?arrow_forward
- Junctional epidermolysis bullosa (JEB) is a severe skin disorder that results in blisters over the entire body. The disorder is caused by autosomal recessive mutations at any one of three loci that help to encode laminin 5, a major component in the dermal–epidermal basement membrane. Leena Pulkkinen and colleagues described a male newborn who was born with JEB and died at 2 months of age (L. Pulkkinen et al. 1997. American Journal of Human Genetics 61:611–619); the child had healthy, unrelated parents. Chromosome analysis revealed that the infant had 46 normal-appearing chromosomes. Analysis of DNA showed that his mother was heterozygous for a JEB-causing allele at the LAMB3 locus, which is on chromosome 1. The father had two normal alleles at this locus. DNA fingerprinting demonstrated that the male assumed to be the father had, in fact, conceived the child. Q. Assuming that no new mutations occurred in this family, explain the presence of an autosomal recessive disease in the child…arrow_forwardJunctional epidermolysis bullosa (JEB) is a severe skin disorder that results in blisters over the entire body. The disorder is caused by autosomal recessive mutations at any one of three loci that help to encode laminin 5, a major component in the dermal–epidermal basement membrane. Leena Pulkkinen and colleagues described a male newborn who was born with JEB and died at 2 months of age (L. Pulkkinen et al. 1997. American Journal of Human Genetics 61:611–619); the child had healthy, unrelated parents. Chromosome analysis revealed that the infant had 46 normal-appearing chromosomes. Analysis of DNA showed that his mother was heterozygous for a JEB-causing allele at the LAMB3 locus, which is on chromosome 1. The father had two normal alleles at this locus. DNA fingerprinting demonstrated that the male assumed to be the father had, in fact, conceived the child. Q. How might you go about proving your explanation? Assume that a number of genetic markers are available for each chromosome.arrow_forwardConsider a Droscophilia fly with a genotype of Nn XqYY. The dominant allele of the sex-linked gene specifies a black body and the recessive a white body. The recessive autosomal allele specifies hairy bristles while the dominant allele specifies smooth bristles. i)What is the ploidy of this fly? ii) What would the sex of this fly be? iii)What would the phenotype of this fly be with respect to these two loci?arrow_forward
- Ehler-Danlos syndrome is a rare disorder caused by a mutation ina gene that encodes a protein called collagen (type 3 A1). Collagenis found in the extracellular matrix that plays an important role inthe formation of skin, joints, and other connective tissues. Peoplewith Ehler-Danlos syndrome have extraordinarily flexible skin and very loose joints. The pedigree below contains several individualsaffected with this syndrome, shown with black symbols. Based onthis pedigree, does the syndrome appear to follow autosomalrecessive, autosomal dominant, X-linked recessive, or X-linkeddominant inheritance? Explain your reasoning.arrow_forwardpeople with osteogenesis imperfecta have a dominant mutation in one of the two genes that produce type 1 collagen. people with OI have weak bones, bkuish color in teh whites of eyes, and a variety of afflictions that cause weakness in their joint and teeth. However, some people can carry the mutation but have no symptoms. Thus, families can unknowingly transmit the mutation but does not express the OI phenotype. This is an example of which of the following? a. incomplete penetrance b. variable expressivity c. epistasis d. incomplete dominancearrow_forwardAnalyze the karyotype shown. Indicate if it is a chromosomal male or achromosomal female. If the karyotype is normal, write the word normal under name or description. If the karyotype is abnormal, name or describethe disorder.arrow_forward
- A 43-year-old (gravida 2, para 2) pregnant woman requests chorionic villus sampling (CVS) and a karyotype of her fetus because of concerns about Down syndrome. Chorionic villus cells reveal the following karyotype: 2 3 7 8 10 11 12 13 14 15 16 17 18 %3D 19 20 21 22 X X Y With this karyotype from CVS, discussion of the results with a genetic counselor would include which one of the following? a. Normal child b. Male with mild to moderate learning problems and infertility c. Female with mild to moderate learning problems and delayed puberty d. Generally normal male, however some degree of short stature and precocious puberty e. Generally normal female, however some degree of short stature and infertilityarrow_forwardFigure 3 shows the karyotypes of two individuals suffering from a genetic disorder. a) Name the genetic disorder for individuals A and B. b) Give three characteristics of individual B. c) What is the gender of individual A?arrow_forwardExplain allelic series. The C-gene expression (Full color, Chinchilla, Himalayan, Albino) with punnet square.arrow_forward
- Human Heredity: Principles and Issues (MindTap Co...BiologyISBN:9781305251052Author:Michael CummingsPublisher:Cengage Learning