A form of dwarfism known as Ellis-van Creveld syndrome was first discovered in the late 1930's, when Richard Ellis and Simon van Creveld shared a train compartment on their way to a pediatrics conference, and discovered 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 syndrome was reported in an Old Order Amish population in eastern Pennsylvania in 1964. In this community with a population of 8000, the observed frequency is 2 per 1000. All affected individuals have unaffected parents, and all affected cases can be traced back to Samuel King and his wife, who arrived in the area in 1774. Neither King nor his wife was affected with the disorder. There are no known cases of the disorder in other Amish communities, such as those in Ohio and Indiana.
From the information given, hypothesize the most likely mode of inheritance (Dominant or recessive? Autosomal or X-linked?) for this disorder. Determine the frequency of the wild-type and Ellis-van Creveld alleles, and calculate the genotype frequencies in the population. What is the most likely explanation for the high frequency of the disorder in the Pennsylvania Amish communities?
A form of dwarfism known as Ellis-van Creveld syndrome was first discovered in the late 1930's, when Richard Ellis and Simon van Creveld shared a train compartment on their way to a pediatrics conference, and discovered 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 syndrome was reported in an Old Order Amish population in eastern Pennsylvania in 1964. In this community with a population of 8000, the observed frequency is 2 per 1000. All affected individuals have unaffected parents, and all affected cases can be traced back to Samuel King and his wife, who arrived in the area in 1774. Neither King nor his wife was affected with the disorder. There are no known cases of the disorder in other Amish communities, such as those in Ohio and Indiana.
From the information given, hypothesize the most likely mode of inheritance (Dominant or recessive? Autosomal or X-linked?) for this disorder. Determine the frequency of the wild-type and Ellis-van Creveld alleles, and calculate the genotype frequencies in the population. What is the most likely explanation for the high frequency of the disorder in the Pennsylvania Amish communities?
