Relating Science to technology, society and the environment.

Impact of evidence, theories, and paradigms on genetics.

Mendel’s Theory Before going into the details of his theory, it’s

important to know a few things:

Dominant genes overshadow recessive genes and are more likely to be passed on to the next generation.

Recessive genes are hidden behind the dominant genes and are therefore less likely to be passed on.

Interesting fact: Mendel’s theory contributed to dog breeding.

Mendel was able to show that:

- if two parents have the same dominant gene (ex: brown eyes), their child will be pure – in other words, he/she too, will have brown eyes.- if however, one parent has a pure dominant gene, and the other has a pure recessive gene, then the child will only be half pure.

So, for example:

If the letter D represents dominant, while R represents recessive, then:

DD would mean two dominants (therefore, one gene from each parent, both containing brown eyes, for example)

DR would mean one parent had a dominant gene, one recessive. In other words, one parent had blue eyes, while the other had brown.

RR would mean both parents had a recessive gene, like blue eyes.

Weissman theory:

The general idea of his theory is that a child receives more from the grandparents than the actual parents. Also, a boy would receive more from the grandmother, while the girl would receive more from the grandfather.

Hershey-Chase Experiment

Objective: To find out whether protein or DNA is the hereditary material.

To do this, they considered the elements that protein and DNA contain. Since DNA contains phosphorous, they labelled it with the radioisotope phosphorous-32. They did the same with protein, but instead used sulfur-35. They discovered that while the phosphorous remained inside the cell, the sulfur was found outside.

Conclusion: DNA carries genes.

Evidence

The discovery of what a gene really was camefrom a study of pneumonia.

Frederick Griffith compared two strains; one caused pneumonia, the other did not. He noticed that the one that caused pneumonia also had a capsule – the other did not.

Results:

- tested on mice- found that the strain causing pneumonia killed the mice, the other did not.- when he used heat to kill the strain that normally caused pneumonia, it no longer did.- when he combined the two strains (the first one, which causes pneumonia, is dead) the mouse somehow caught pneumonia.…

He proposed two hypothesis from this experiment. Either the dead strain had suddenly come to life, or the strain that did not initially cause pneumonia somehow transformed into the one that did.

He later found that his second hypothesis was right.

References:

• Farabee, M. (2006). DNA and Molecular Genetics. April 13, 2009. On-Line Biology Book.http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookDNAMOLGEN.html

• Scofield, T. (1975). Theories of Genetics. April 13, 2009. Health and Genetics Information. http://www.awsaclub.com/healthgenetics/theoriesofgentics.htm