Use the following pedigree (Figure 14.3) for a family in which dark-shaded symbols represent individuals with one of the two major types of colon cancer. Numbers under the symbols are the individual's age at the time of diagnosis.

Figure 14.3
-In each generation of this family after generation I, the age at diagnosis is significantly lower than would be found in nonfamilial (sporadic)cases of this cancer (~ 63 years). What is the most likely reason?
A) Members of this family know to be checked for colon cancer early in life.
B) Hereditary (or familial) cases of this cancer typically occur at earlier ages than do nonfamilial forms.
C) This is pure chance; it would not be expected if you were to look at a different family.
D) This cancer requires mutations in more than this one gene.
E) Affected members of this family are born with colon cancer, and it can be detected whenever they are first tested.

Question

Use the following pedigree (Figure 14.3) for a family in which dark-shaded symbols represent individuals with one of the two major types of colon cancer. Numbers under the symbols are the individual's age at the time of diagnosis.
  
Figure 14.3
-In each generation of this family after generation I, the age at diagnosis is significantly lower than would be found in nonfamilial (sporadic)cases of this cancer (~ 63 years). What is the most likely reason?
A) Members of this family know to be checked for colon cancer early in life. 
B) Hereditary (or familial) cases of this cancer typically occur at earlier ages than do nonfamilial forms. 
C) This is pure chance; it would not be expected if you were to look at a different family. 
D) This cancer requires mutations in more than this one gene. 
E) Affected members of this family are born with colon cancer, and it can be detected whenever they are first tested.

Quizplus · Accepted Answer

Hereditary (or familial) cases of colon cancer typically occur at earlier ages than nonfamilial cases. This suggests that this family has an inherited genetic predisposition for colon cancer, which leads to earlier onset of the disease than in sporadic cases. The fact that this pattern is seen in every generation after the first also supports the idea of an inherited mutation. Option A is not a likely explanation because it does not explain the consistent pattern of early onset of colon cancer in this family. Option C is incorrect because the pattern of early onset is observed in this family and is not due to chance. Option D is possible, but the pedigree does not provide evidence for this explanation. Option E is not correct because colon cancer is not present at birth and typically takes many years to develop.

Use the Following Pedigree (Figure 14