Exam 4: Principles of Genetic Variation

Fill in the blanks below. The DNA in our cells is susceptible to damage as a result of exposure to harmful radiation or to ____1____ mutagens. Excess exposure to ___2____ radiation within sunlight, for example, or to tobacco carcinogens induces harmful changes in our DNA. However, the most frequent changes in the base sequence of our DNA arise from _____3____ sources, arising from proximity to harmful chemicals within our cells, notably ____4____ ____5____ ____6____ , and as a consequence of occasional errors in various ____3____ mechanisms, such as DNA ____7____, DNA ____8____ , and chromosome ____9_____.

With reference to base cross-linking, which, if any, of the following statements, is false?

On the diagram below, identify the covalent bonds that are susceptible to breakage as a result of oxidative damage.

Fill in the blanks below. In the nuclear genome, a ___1____ means a unique location for A DNA sequence. At each diploid ___1____ a person has inherited two ___2____ , one that is paternally inherited and one that is maternally inherited. If the maternal and paternal ___2____ are identical, the person is said to be ____3____ at that ____1____, but if the maternal and paternal _____2_____ differ by even a single nucleotide, the person is said to be ____4_____ at that locus. Whereas women have 23 pairs of homologous chromosomes, men have 22 pairs of autosomal homologs but very different sex chromosomes. As a result, most of the DNA sequences on the X and on the Y chromosomes do not have a counterpart on the other sex chromosome. A ___1____on the X chromosome in men often, therefore, has just a maternal ____2____ , and most loci on the Y have just a paternal ____2____ allele. At loci like these, a man would be said to be _____5_____.

With reference to DNA repair, which of the following statements, if any, is false?

With reference to positive selection, what is meant by a selective sweep?

What are single nucleotide polymorphisms and why do they occur at only certain nucleotides in our genome?

Longer microsatellites are very prone to being polymorphic. What are microsatellites, why should long microsatellites be so prone to being polymorphic, and what is the mechanism that is responsible for the polymorphism?

With reference to reactive oxygen species (ROS), which of the following statements, if any, is false? a) ROS are an inevitable consequence of the chemical reactions that occur in cells and are formed by the incomplete one-electron reduction of oxygen. b) Common examples of ROS include hydrogen peroxide (H₂O₂), superoxide anions (O₂^-) and hydroxyl radicals (OH^.). c) ROS are generated in different intracellular compartments, but notably in mitochondria. d) ROS are functionally valuable: they play important roles in both intercellular and intracellular signalling.

With reference to DNA repair, which of the following statements, if any, is false?

On the diagram below, identify the covalent bonds that are susceptible to breakage as a result of hydrolytic damage causing depyrimidination.

What, approximately, is the fraction of genetic variation in the nuclear genome is that is expected to have a harmful effect on gene function?

The HLA system is important in medicine for two major reasons. What are they?

Match individual environmental factors a) to e) to associated types of chemical damage to DNA i) to iv)

Which, if any, of the following statements is false?

A human zygote has three immunoglobulin loci, one that specifies the heavy chain and two that specify the light chain. Taking into account differences between maternal and paternal alleles a B cell might be expected to have the potential of making a total of two different heavy chains and four different light chains, and therefore eight different immunoglobulins. Instead, each mature B cell makes just a single type of immunoglobulin. How does that happen?

Match the types of DNA damage a) to g) to the most appropriate of the DNA repair mechanisms i) to v) that can be expected to repair the damage.

With reference to hydrolytic damage to DNA which of the following statements, if any, is false?

"The huge variation in immunoglobulins and T cell receptors is manifest at the level of the individual, but the huge variation in HLA proteins is expressed at the level of the population". What is meant by this statement?

Which, if any, of the following statements is incorrect?