Why is our genetic code degenerate?

To answer this question, it is first important to understand the meaning of the word degenerate.

So being an A level Biology student, you must know that genes code for amino acids. (these are the basic components of protiens)

Now, each amino acid is coded for by a triad sequence of bases , namely Adenine, Cystine, Thyamine and Guanine (Thyamine is replaced by Uracil in RNA, if we are referring to codons instead of anticodons). These bases are referred to by the capitalised form of their first letter i.e. A,C,T,G,U. Hence, an amino acid is coded for by an codon with the sequence: AUG, or GUA, or GGA (Any combination really of A,G,C,U) 

There are 20 amino acids that need to be coded for in humans. Therefore there should be 20 sets of triplet sequences, however because of simple maths ( that I will show shortly) , there are actually 64 combinations/triad codes available which means that some amino acids have a repetitive code i.e. the code is degenerate. For example, the amino acid Cystiene is coded for by the codons UGU AND UGC. Some amino acids have up to six combinations for just themselves.

So here is the maths: 

We have four bases available: A , G , C and U 

And we have to code for 20 Amino acids. 

If each Amino acid was coded for by 2 bases, we would only have 16 possible combinations, which is four short of how many we need: 4 x 4 = 16

_ _ 

(Four options in the first blank, four options in the second blank as the code can be repeated and be in any arrangement, there fore it is 4 x 4 ) 

Now the next option is to have three bases code for each amino acid : 

_ _ _ 

So four options in the first, four options in the second and four options in the third. Therefore 4 x 4 x 4 or 4which is 64 ! Thats how many we have -which is more than the 20 we need and hence the code is degenerate!

Obviously four bases coding for an amino acid would mean 44 and so on... many many more than we actually need!

Amna  A. 13 plus  Physics tutor, 13 plus  Biology tutor, A Level Math...

1 year ago

Answered by Amna , an A Level Biology tutor with MyTutor

Still stuck? Get one-to-one help from a personally interviewed subject specialist


Elizabeth T. A Level Biology tutor, GCSE Biology tutor, GCSE History ...
View profile
£20 /hr

Elizabeth T.

Degree: Biomedical Science (Bachelors) - Newcastle University

Subjects offered: Biology, Chemistry


“A Little Bit About Lizzie: I am a Biomedical Science student studying at Newcastle University. I recieved grade A's in Biology, Chemistry and Maths at A-level, and have always had a real passion for science! I am patient and have a v...”

Zoe C. A Level Biology tutor, GCSE Biology tutor, A Level Geography t...
View profile
£20 /hr

Zoe C.

Degree: Biological Sciences (Bachelors) - Exeter University

Subjects offered: Biology, Geography+ 1 more


“My name is Zoe and I am currently studying biological sciences at the University of Exeter. I absolutley love science and I would love to tutor you so you can discover the wonders of science too. At A level I studied biology, chemistr...”

Oli W. A Level Biology tutor, GCSE Biology tutor, A Level Maths tutor...
View profile
£20 /hr

Oli W.

Degree: Bachelor of Medicine, Bachelor of Surgery (MBChB) (Bachelors) - Birmingham University

Subjects offered: Biology, Physics+ 2 more

-Medical School Preparation-

“Hi! My name is Oli and I'm currently studying medicine at the University of Birmingham. Having been keen on sciences all throughout school, I'd love to share my passion through tutoring! After carrying on all of the sciences through ...”

MyTutor guarantee

About the author

Amna  A. 13 plus  Physics tutor, 13 plus  Biology tutor, A Level Math...
View profile

Amna A.

Currently unavailable: for regular students

Degree: Biomedical Engineering (Masters) - Imperial College London University

Subjects offered: Biology, Science+ 2 more


“Hi, I'm Amna and I study Biomedical Engineering at Imperial College London. In my course, we cover stuff from all areas in Maths, Physics, Chemistry and Biology! I have studied science since GCSE at which I got 9A*'s and I managed to ...”

You may also like...

Other A Level Biology questions

Explain why an enzyme catalyses only one reaction.

What is the difference beween biological species concept and the phylogentic approach to defining species?

How does an action potential cause contraction in skeletal muscle?

How does eutrophication work?

View A Level Biology tutors


We use cookies to improve our service. By continuing to use this website, we'll assume that you're OK with this. Dismiss