Author: wohlwila

Test

The elucidation of the structure of the double helix provided a hint as to how DNA divides and makes copies of itself. This model suggests that the two strands of the double helix separate during replication, and each strand serves as a template from which the new complementary strand is copied. What was not clear was how the replication took place. There were three models suggested (Figure): conservative, semi-conservative, and dispersive.

Illustration shows the conservative, semi-conservative, and dispersive models of DNA synthesis. In the conservative model, when DNA is replicated and both newly synthesized strands are paired together. In the semi-conservative model, each newly synthesized strand pairs with a parent strand. In the dispersive model, newly synthesized DNA is interspersed with parent DNA within both DNA strands.
The three suggested models of DNA replication. Grey indicates the original DNA strands, and blue indicates newly synthesized DNA.

In conservative replication, the parental DNA remains together, and the newly formed daughter strands are together. The semi-conservative method suggests that each of the two parental DNA strands act as a template for new DNA to be synthesized; after replication, each double-stranded DNA includes one parental or “old” strand and one “new” strand. In the dispersive model, both copies of DNA have double-stranded segments of parental DNA and newly synthesized DNA interspersed.

Meselson and Stahl were interested in understanding how DNA replicates. They grew E. coli for several generations in a medium containing a “heavy” isotope of nitrogen (15N) that gets incorporated into nitrogenous bases, and eventually into the DNA (Figure).

Illustration shows an experiment in which E. coli was grown initially in media containing ^{15}N nucleotides. When the DNA was extracted and run in an ultracentrifuge, a band of DNA appeared low in the tube. The culture was next placed in ^{14}N medium. After one generation, all of the DNA appeared in the middle of the tube, indicating that the DNA was a mixture of half ^{14}N and half ^{15}N DNA. After two generations, half of the DNA appeared in the middle of the tube, and half appeared higher up, indicating that half the DNA contained 50% ^{15}N, and half contained ^{14}N only. In subsequent generations, more and more of the DNA appeared in the upper, ^{14}N band.

 

 

Gender Determination Exercise

Go to http://www.hhmi.org/biointeractive/gender-testing-athletes

Go through the exercise and say whether you decided that Jane was qualified or not qualified to compete in the athletic events. Give your reasoning. Also, after completing the exercise, briefly state, in your own words what you learned about CAIS.

Give your answer in the “leave a reply” section below

Musuclar Dystrophy and Medical Ethics

Read the following:


Then answer the following questions:

Would you expect the 2 daughters of the mother in the article to have a chance to have sons with muscular dystrophy? Explain.

Should we as a society spend more or less on diseases like Duchenne muscular dystrophy? Note that Duchenne Muscular dystrophy is fairly common compared to most single gene diseases, but much rarer than conditions like heart disease or autism.

If a cure is found but it is very expensive, should it be available to everybody? Why or why not?

A doctor in that article made (what I believe) to be a serious ethical error. What was it? Discuss.

Write your answers as a reply in the comments section

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