Blackwell Publishing

Molecular and Mendelian Genetics - Is there non-coding DNA?


A large proportion of the genome is non coding

This table shows the amount of DNA and percentage of single copy DNA (sc DNA.) It suggests there is a large quantity of non-informational DNA:

1. The figures for single copy DNA are much less than 100%: only one fifth of the amphibian Necturus masculoscus is single copy DNA, suggesting that nine tenths is non-coding.

2. The large differences in genome sizes between species. It is unlikely that these differences are entirely due to differences in the numbers of informational genes. In the words of Orgel and Crick:

"It seems implausible that the number of radically different genes needed in a salamander is 20 times that in a man."

It would seem therefore that a large part of the genome is non-coding, repetitive DNA.

Table: amount of DNA and percentage of single copy DNA (sc DNA) in various animal species. Amount of DNA is expressed as haploid DNA content, 1C in picograms. From John and Miklos (1988).

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