Question

1. In 1972, Susumu Ohno, a Japanese geneticist observed noncoding DNA sections, and coined the term junk DNA. He observed that most of these segments in genomes sometimes move to different positions within the genome. Later researchers observed important phenomena related to evolution, and had to rethink in terms of calling these junk DNA.
2. What is the important molecular phenomenon observed by Ohno in terms of the “movement” within the genome
3. What in reality is the junk DNA?
4. What is the evolutionary phenomenon that made later researchers rethink about junk DNA term?
5. In the junk DNA, there are “duplicate” genes and “repeats”? What do you think is the difference between the two?

Answer 1

The phenomenon observed by the scientist where of Transposable elements. These are also called as jumping genes, because of their ability to jump from one place to another place within the genome. These are the sequences within a specific set of codes in the DNA.

A junk DNA is the one which does not code for protein or RNA. It is usually present as intron within coding sequences. Large part of the junk DNA contains repetitive sequences.

Junk DNA was first believed as useless burden carried by the organisms. But as the genome studies widened, the junk DNA was found to contain repeat sequences which had roles to play in epigenetics. Some junk DNA were transposable elements, which could randomly cause mutations, turn off and on gene expressions. Now research focuses on certain aspects of junk DNA which have role to play in chromosome modelling, gene expression regulations and organ specific gene expressions.. etc. The junk DNA also contain several conserved sequences across all the organisms and their low rate of mutation has made researchers rethink on their role in genome complexity.

The duplicate genes are two copies of same gene. A gene can be present as two copies on same chromosome. In the case of repeats a small code may be triplet or hexaplet is repeated multiple times.