Case Workbook for Human Genetics 9th Edition by Ricki Lewis

Exercise 1

For each situation described below, indicate which of the following phenomena occurs:
a. incomplete penetrance
d. genetic heterogeneity
b. variable expressivity
e. pleiotropy
c. phenocopy
f. genomic imprinting
a.Genes for manic depression are on chromosomes 18 and 21.
b.Benign epidermolysis bullosa causes loss of skin, hair, eyelashes, and abnormal nails and teeth. These symptoms result from an abnormal collagen gene.
c.Prader-Willi syndrome results from deletion of the paternal copy of a part of chromosome 15, but an entirely different disorder, Angelman syndrome, results from loss of the maternal counterpart to this region.
d.Genes that cause deafness are on chromosomes 6, 11, 17 and 19.
e.Late-onset cardiac amyloidosis causes heart failure. The gene was sequenced, and in some families, found to be mutant in a few individuals who have healthy hearts.
f.A child with Cornelia deLange syndrome has an elf-like face, difficulty feeding and speaking, developmental delay, limb reduction, and is very small. Affected children with a.bnormal faces and very low weight, but with normal limbs, are often misdiagnosed.
g.Barth syndrome, severe X-linked cardiomyopathy, and X-linked endocardial fibroelastosis were thought to be distinct, because of differing degrees of damage to heart muscle, until gene sequencing revealed that they result from mutations in the same gene.
hIn dilated cardiomyopathy, heart chambers enlarge and the person may die of congestive heart failure. The condition may be caused by any of three genes, a malfunctioning immune system, or by exposure to toxins.