Name: _________________________________________
Directions: Read through each scenario and determine the word which best describes the
genetic phenomenon occurring. Your choices are Genetic heterogeneity, Variable
Expressivity, Incomplete Penetrance, Phenocopy, Pleiotropy.
1. The allele SP is responsible for piebald spotting in a species of beagles. Below are
examples of piebald spotting.
2. Marfan’s syndrome is a disorder of the fibrous connective tissue characterize by many
symptoms, including long, thin digits; eye defect; heart disease; and long limbs. Flo
Hyman, an American volleyball star, died from marfan’s syndrome, where soon after a
game she ruptured her aorta.
3. Rubella embryopathy causes infant deafness. This deafness is caused by an infection
of the mother during her first trimester.
4. King George III ruled England during the American Revolution. At age 50 he first
experienced abdominal pains and constipations, followed by weak limbs, fever, and a fast
pulse, hoarseness, and dark red urine. Followed soon by nervous system symptoms such
as insomnia, headaches, visual problems, restlessness, delirium, and convulsions. His
confused and racing thoughts, combined with actions such as ripping off his wig and
running about naked while at the peak of a fever, convinced court observers that the king
was mad. Just as Parliament was debating his ability to rule, he mysteriously recovered.
5. BRCA1 is the leading cause of breast cancer. Inherited as an autosomal gene, more
women are affected by the disorder than men, yet the same number of men and woman
may be carriers for the BRCA 1 gene.
6. There are 132 forms of deafness transmitted as autosomal recessive traits, where if a
man is heterozygous for the deafness for one type and the mother is heterozygous for the
deafness for another type, the child’s chances of developing deafness do not increase
since they will be passing on the recessive allele for completely different genes.
7. A person suffering from cystic fibrosis has symptoms ranging from mild bronchial
symptoms to severe lung deficiencies where it could be fatal by the age of 30.
8. The Smith family was told that contacting a genetic counselor to determine the
likelihood for the development of alzheimer’s might be difficult because of the many
different genes that cause the disorder.
9. Following an injury on the football field, Thomas noticed his blood sugar was all over
the place. He went to the doctor and neglected to tell him about the injury, and the doctor
said that you may have diabetes.
10. A woman has severe neurofibromatosis type I. She has brown spots on her skin and
several large tumors beneath her skin. A gene test shows that her son has inherited the
disease-causing autosomal dominant allele, but he has no symptoms.
11. Patients with thalassemia, a disorder caused by defective beta-globin synthesis, have
diverse clinical characteristics Patients with severe cases have profound anemia and
require regular blood transfusions, while other individuals who carry the same allele have
mild and undetectable symptoms
12. In fruit fly, Drosophila melanogaster, the normal body color is brownish-gray with
black stripes along the abdomen. This was a genotypic character which was constant in
both the flies in all environments. However, in 1939, Rapport discovered that if larva of
normal flies were fed with silver salts, they develop into yellow bodied flies irrespective
of their genotype.
13. In the fruit fly Drosophila, the vestigial gene plays a critical role in wing
development. In fact, if these flies are homozygous for the recessive form of the vestigial
gene (vg), they will develop short wings, and they will be unable to fly as a direct result.
Along with regulating wing development, the gene changes the number of egg strings in
a fly's ovaries, alters the position of bristles on a fly's scutellum, and decreases the length
of a fly's life.
14. Retina pigmentosa is characterized by mottling of the retinal pigment epithelium with
black bone-spicule pigmentation is typically indicative (or pathognomonic) of retinitis
pigmentosa. It has been determined that its mode of inheritance can be sex-linked
recessive, autosomal dominant, or in some cases autosomal recessive.