20 - But wait a minute, how do we know that DNA is...

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But wait a minute, how do we know that DNA is responsible for heritable traits? Two important experiments, both using bacteria. Frederick Griffith showed that a lethal trait (heritable unit) could be transformed from one strain of bacteria to a different strain of the same species. What was the molecule that transferred the trait was not determined. Hershey and Chase (1952) wanted to determine if the heritable unit was a protein or DNA. They did so by using radioactive DNA and radioactive protein to determine what was transferred during the replication of viral DNA (p182 – 183). A virus that replicates inside of bacteria was produced so that either the DNA or the protein had a radioactive tracer; but not both. The virus was then incubated with the bacteria. In the bacteria, only the DNA was found to contain the radioactive tracer, not the protein. This experiment showed that DNA contained the heritable trait. So, now I can confidently continue talking about DNA and inheritance. 1
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chromosome. This also means that there is only a single copy of a gene. What is a gene? The basic unit of inheritance. It is a length of nucleotides along a discrete portion of the DNA molecule that code for a product. A gene has a start point (an on/off switch), a length of message (nucleotides that actually code for the product) and an end point (a short sequence of nucleotides that say THE END). Do all cells have only a single copy of each gene? NO Most eukaryotes have two copies of each chromosome which means they have two copies of each gene. If a cell has two copies of identical chromosomes it is a DIPLOID. This is not the same as a cell that has multiple unique chromosomes. For instance, humans have 23 unique chromosomes and two copies of each chromosome. Human somatic cells are diploids because they have two
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This note was uploaded on 04/07/2008 for the course BIOS 101 taught by Professor Plantz during the Spring '08 term at UNL.

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20 - But wait a minute, how do we know that DNA is...

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