Several species of sea urchins may inhabit the same tide pool and their reproductive periods overlap. Although they practice external fertilization, they seldom interbreed because eggs produce chemicals that are only attractive to sperm of their own species. This is an example of a ________ barrier that ________.

A mutation in the promoter region of the gene for the clotting factor IX is the cause of hemophilia B, which results in insufficient clotting. What is the likely reason for hemophilia?

Does alternative gene splicing increase or decrease the flexibility of gene expression? Explain your answer.

During development in the mother’s uterus, human embryos have pharyngeal pouches (sometimes called gill slits) that later develop into various glands. Fish also have pharyngeal pouches as embryos, but these develop into gills. The best explanation for why human and fish embryos develop pharyngeal pouches is

What would happen if RNA polymerase II did not have proofreading capabilities?

Coloration in the peppered moth (Biston betularia) is determined by a single gene with two alleles showing complete dominance. Dark moths are homozygous dominant or heterozygous for the gene, light moths are homozygous recessive. In a sample of 100 moths, you determine that 64 of the moths are dark. According to the Hardy-Weinberg rule, the expected frequency of the dominant allele is ________.

New drugs are being developed that decrease DNA methylation and prevent the removal of acetyl groups from histone proteins. Explain how these drugs could affect gene expression to help kill tumor cells.

Two parents who do not have sickle cell anemia have a child that has the disease.  The parents are both:

If mRNA is complementary to the DNA template strand and the DNA template stand is complementary to the DNA non-template strand, why are base sequences of mRNA and the DNA non-template strand not identical? Could they ever be?

New drugs are being developed that decrease DNA methylation and prevent the removal of acetyl groups from histone proteins. Explain how these drugs could affect gene expression to help kill tumor cells.