A man known to be a carrier of a genetic disease affecting a lysosomal enzyme has no symptoms of the disease. However, when the enzyme activity is actually measured, it is seen that the man's cells have half the activity as those from someone who is homozygous dominant. Can this allele be considered to be completely dominant? What would such a situation suggest for the treatment of patients with this genetic disease?
Not all individuals with Down syndrome have equally severe mental retardation or other physical abnormalities. Explain on the basis of a difference in the expression of alleles.
The particular recessive allele that causes cystic fibrosis (CF) can vary. Seventy percent of patients with CF are homozygous recessive for one particular allele, but 30% are homozygous recessive for any number of different alleles that also cause CF. The screening test for heterozygotes detects only the most common allele for CF. If a person with CF relatives, tests negative for the common allele how might she/he determine that she/he need not worry about the possibility of having a rarer form of the CF allele?
In patients with chronic myelogenous leukemia, one sees an odd chromosome in all of the cancerous cells. A small piece of chromosome 9 is connected to chromosome 22. This 9:22 translocation has been termed the Philadelphia chromosome. How could a translocation cause genetic changes that result in cancer?
