chapter 14

• Every day we observe heritable variations (such as brown, green, or blue eyes) among individuals in a population.
• These traits are transmitted from parents to offspring.
• One possible explanation for heredity is a “blending” hypothesis.
  • This hypothesis proposes that genetic material contributed by each parent mixes in a manner analogous to the way blue and yellow paints blend to make green.
  • With blending inheritance, a freely mating population will eventually give rise to a uniform population of individuals.
  • Everyday observations and the results of breeding experiments tell us that heritable traits do not blend to become uniform.
• An alternative model, “particulate” inheritance, proposes that parents pass on discrete heritable units, genes, that retain their separate identities in offspring.
  • Genes can be sorted and passed on, generation after generation, in undiluted form.
• Modern genetics began in an abbey garden, where a monk named Gregor Mendel documented a particulate mechanism of inheritance.

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.

What is the genotype of the deceased individual in generation II?

A) homozygous for a gene for colon cancer
B) homozygous for both cancer alleles from his mother
C) heterozygous for a gene for colon cancer

D) affected by the same colon cancer environmental factor as his mother
E) carrier of all of the several known genes for colon cancer

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.

From this pedigree, how does this trait seem to be inherited?

A) from mothers
B) as an autosomal recessive
C) as a result of epistasis
D) as an autosomal dominant
E) as an incomplete dominant