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

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

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.

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

From a standpoint of natural selection,we see that the heterozygous advantage for βᴬβˢ 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 βˢ alleles is equal.What is the term for this stable condition that allows mutant alleles to remain in a particular population?

The mutation that causes SCD causes what kind of change in the structure of hemoglobin?

We can detect the SNP in the βˢ allele because it destroys a DdeI restriction site,leading to DNA restriction fragment variation revealed by Southern blot analysis. Either two or three restriction sequences for the restriction endonuclease DdeI can occur near the β-globin gene,depending on the allele.One DdeI restriction sequence is eliminated from the βˢ allele by the SNP in the mutant allele because of a mutation in the double-stranded target sequence 5′ - CTNAG - 3′. Suppose the wild-type allele sequence is CCTGAG,while a newly identified SNP is CCTTAG.Would this same restriction fragment analysis technique be appropriate for detecting this particular SNP? What other technique(s)could you use to identify this particular mutation?

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?

Given the following gel,which protein has a more negative charge?

Being a carrier of the sickle cell trait,although generally not a serious problem,can pose significant risks for athletes,particularly those in intense training regimens.The death of Florida State University linebacker Devaughn Darling,a carrier of the sickle cell trait,in a spring conditioning drill refocused attention on sickle cell abnormalities,including both sickle cell disease and sickle cell trait (carriers).High altitude,aggressive exercise,and high temperatures can all lead to acute rhabdomyolysis in individuals with sickle cell trait.Why do you think an individual who is a carrier of the sickle cell trait may be more likely to experience the symptoms of SCD during rigorous exercise?

Which of the following techniques describes either the rate of a molecule's migration or its final position in a gel?

Given the following gel,which DNA fragment has a lower electrophoretic mobility?

A SNP results in a loss of the XhoI site indicated,so you design a molecular probe that spans the lost XhoI site.Which lane represents the expected Southern blot of an individual who is a carrier (heterozygous)for the mutant allele?

Pauling used gel electrophoresis to confirm that homozygous individuals produce a single form of β-globin protein that differs depending on the homozygous genotype as well as that heterozygotes produce proteins of both types in approximately equal concentration.What characteristic(s)of the bands proved this?

We saw that Southern blotting of DNA from the βᴬ 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 βˢ-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 bandsif 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?

Sickle cell is a codominant disease,meaning that heterozygotes exhibit an intermediate blood cell phenotype (a mixture of normal and sickle cells)due to the blend of hemoglobin tetramers in each red blood cell.Which of the following tetramer structures would you expect to find in a carrier of SCD?

In contrast to the nucleic acid probes used to detect DNA or RNA target sequences,molecular probes used to detect target proteins in western blots are ________.

Hemoglobin,the protein responsible for binding and transporting oxygen,forms a tetramer.What is the protein composition of the most common form of hemoglobin,hemoglobin A (HbA)?

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

Northern blotting is not useful in detecting the SNPs associated with the βᴬ and βˢ alleles.Explain why.

At a biological level,βᴬβˢ heterozygotes suffer fewer cases of malaria than βᴬβᴬ homozygotes,and when they do get malaria,their disease is less severe.What is the biological explanation for the heterozygous advantage?