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Heredity
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In search of the gene.

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Henderson's Dictionary of Biological Terms. 10th Ed. John Wiley & Sons.


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Heredity



In Search Of The Gene

DNA deoxyribonucleic acid, is a nucleic acid made of two strands of nucleotides wound around each other in a shape that forms a double helix. DNA can be found in all living organisms and viruses. I believe that the start of the discovery of all the information that we have on DNA began with Gregor Mendel.

Gregor Mendel was a monk who lived in a monastery. In 1846 Gregor predicted the patterns of inheritance. He began by studying peas, and all of the varying traits they had to offer like round or wrinkled, or yellow and green and many others. Later Mendel introduced two laws. The first one was called the Law of Segregation, the his next law was the Law of Independent Assortment. Then Mendel proposed a theory of heredity, and it wasn't until later (1900) that they found his work useful and published it.

Frederick Griffith made and accidental discovery about DNA, while he was trying to find or prepare a vaccine against the pneumonia bacteria. He worked with two types of strains of the Streptococcus pneumonae. The first strain was in a capsule that was made of polysaccharides. The capsules were meant to protect the body against the bacterium in the defense system. Then Oswald Avery and his biologist co-workers showed that in numerous experiments that the material for transformation of DNA was destroyed when a DNA destroying enzyme was present.

In 1952 Alfred Hershey and Martha Chase used a type of bacteriophage (a virus that infects bacteria). First they grew one batch of a phage that had a radioactive phosphorus, and then another batch with a radioactive sulfur. They then infected the Escherchia coli bacteria with 35S -labeled phages. Then they mixed the bacteria. When they studied the layers they saw that most of the 32P was part of the bacteria. This showed that the DNA stores the genetic information..

In 1949 Erwin Chargoff discovered that the amount of Adenine always equals the amount of Thymine, just as Guanine and Cytosine are always equal. It was implied that the arrangement of the nucleotides within a DNA molecules are the specific genes.

Then in 1952 Maurice Wilkins and Rosalind Franklin Developed some x-rays photographs of DNA molecules. They thought that maybe the DNA molecule looked like a tight coiled helix and was made of two or three chains of nucleotides.

Last but not least in 1953 James Watson and Francis Crick built a model of DNA by using the x-ray pictures. After they built it was determined that it was a spiral staircase or now better known as a double helix ladder, with two strands of nucleotides twisted around a central axis.

So in conclusion the discovery of DNA had greatly progressed throughout all these years. It began with Mendel and his crossbreeding and ended with the discovery of the shape of DNA by building a model and we are still going.

By Danielle Sullivan
6.13.01