Question: A form of dwarfism known as Ellis-van Creveld syndrome was first discovered in the late 1930’s, w…

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?