Barbara McClintock | Discovery of Jumping genes | Experiment

 Barbara McClintock 

Barbara McClintock

Barbara McClintock discovers the jumping genes. She discovered this in the cells of maize.

Now, what are jumping genes?

Jumping genes are also called transposons or mobile genes. They are part of DNA that can move and can jump from one position to another position within the genes of chromosomes.

Maize has 10 numbers of total chromosomes and McClintock was studying chromosome number 9. 

The numbering of these chromosomes also had a logic behind it, the largest size chromosome is taken as first while the smallest size was taken as the last number of chromosomes.

• She was observing maize for several years and studied the breakage of chromosomes in maize. She noticed a particular breakage in chromosome number 9 of the same locus many times. She named this Ds or dissociation.
• She also discovered that Ds is dependent on Ac. 
• The Ac means activator because an activator is essential for Ds to move within the genome. She called these transposons.
• It was very difficult for scientists to accept that thing that genes can move within the genome but she got a Nobel prize for her excellent work in 1983.
• She observed in her experiment that Ds only affect the color of maize. 

She also observed that maize shows four different characters. She got the phenotypes of maize:

1. Fully colored maize
2. Fully colorless maize
3. Partially pigmented or colored
4. Partially unpigmented or colorless

1. She called pigmented maize, normal maize because the gene of color is not broken from any point.
2. She said unpigmented maize affected maize because the gene of the color showed breakage in the presence of Ac(activator).
3. She defends partially pigmented maize as initially it was normal maize that shows color but later it breaks from its genome and it shows a colorless appearance.
4. She defends partially unpigmented maize as the gene of color was not broken from any point. It was affected by Ds because it attached to the color gene and can cause mutation in the color of maize. She also observed that mutation is also caused by Ac.  

It was shown in her experiment that the Ds not only break the genes but can also be attached to another genome and cause mutation in it. That’s why they are called jumping genes or mobile genes because they can move.