Exam 10: The Integration of Genetic Approaches: Understanding Sickle Cell Disease

What term is used to describe the situation when the loss of an allele because of selection against one of its phenotypes is balanced by natural selection in favor of the allele for another phenotype?

Given the following gel, which DNA fragment has a lower molecular mass?

How is the DNA visualized on a Southern blot?

Which of the following images represents the expected results of a DNA gel for three individuals with different genotypes-homozygous dominant (lane 1), heterozygote (lane 2), and homozygous recessive (lane 3)?

The intercalating agent ________ allows researchers to visualize DNA and RNA on a gel when the gel is exposed to UV light.

Given what you know of the inheritance pattern of SCD, what can be said of individual II-5?

From a standpoint of natural selection, we see that the heterozygous advantage for β^Aβ^S individuals is balanced by the disadvantage to those with SCD or the wild-type alleles (and no malaria protection). The action of these conflicting trends produces an overall increase in the mutant allele until it reaches a state where the gain and loss of β^S alleles is equal. What is the term for this stable condition that allows mutant alleles to remain in a particular population?

We saw that Southern blotting of DNA from the β^A allele produces two DNA bands corresponding to fragment lengths of 1150 bp and 200 bp based on the location of two DdeI sites. In contrast, Southern blot analysis of β^S-allele DNA produces a single DNA restriction fragment, measuring 1350 bp in length, since one of the DdeI sites is altered by SNP variation. Why is Southern blotting necessary to identify the correct bands-if you know the sizes, why can't you just identify your band on a gel? Why is the location of the probe (spanning the predicted lost DdeI site)important?

Ingram examined hemoglobin structural variation by breaking down the hemoglobin protein into many fragments by chemical treatment and subjecting the fragments to electrophoresis to separate them in a gel; and then in a second dimension, perpendicular to the first, he separated them by chromatography. This two-step approach is commonly referred to as __________.

Thalassemia is a recessive blood disease caused by reduced synthesis of one of the globin genes. While SCD is a mutation in the structure of hemoglobin, thalassemias can also be caused by mutations in the regulatory elements, causing too little globin to be produced and resulting in anemia. You've designed a DNA probe that you want to use to screen a family for a rare mutation in the β-globin gene that causes thalassemia. First you will use the probe for northern blotting. What information will the northern blot tell you?

Which of the following techniques quantifies the amount of protein present in a gel lane by measuring how much light is blocked from passing through the gel by the presence of a band of protein?

Based only on this Southern blot and with no knowledge of which of the β-globin SNPs you are looking at, which lane(s)might represent(s)a heterozygous individual?

You set up an EcoRI restriction digest for a sample of genomic DNA from an individual with a mutation in the β-globin gene. You perform a Southern blot using the entire β-globin gene as a probe. To your surprise, you notice a different pattern of bands in the affected individual - you have identified a new SNP! What can you conclude from the pattern of bands from the Southern blot below?

The bone marrow must continuously generate new red blood cells because the life span of a typical red blood cell is only ________. The life span is even shorter in individuals with sickle-cell trait, which accounts for the protective effects against malaria.

Burkitt's lymphoma is a cancer of the lymphatic system. The endemic variant, common to equatorial Africa, commonly affects children who are also affected by chronic malaria. A recent study found that individuals with AA hemoglobin were twice as likely to develop Burkitt's lymphoma as those with the AS genotype. We saw a similar benefit of certain genotypes in cases of sickle cell disease. Recall that individuals who are β^Aβ^S, β^Aβ^C, or β^Aβ^E have a survival and reproductive advantage over individuals who are homozygous β^Aβ^A (and therefore succumb more easily to malaria)and over those who are homozygous for the mutant alleles (and therefore suffer from hereditary anemia). Resistance to malaria and Burkitt's lymphoma are both an example of ________ advantage.

A couple has four children; one is affected by SCD, and two are carriers of the disease. What can be said of the genotypes of the parents?

Given the following plasmid, what are the sizes of the fragments you would expect from an XhoI digest?

Molecular charge is an important characteristic influencing protein migration on a gel. What accounts for the variation in the molecular charge of proteins?

What information allows you to predict the pattern of DNA bands expected in a Southern blot of an individual with the wild-type allele?

Describe the hypothesis that James Neel proposed to describe the inheritance pattern of SCD. What experimental methods did he use to prove his hypothesis?