All UK Exam Boards included

Genetic Comparisons

This is a legacy topic. View the most up to date content by selecting the exam board in the dropdown to the left.


More reliable and accurate than mere physical resemblance in determining the genetic relationship between individuals and species, is of course a genetic comparison. This can be achieved either by directly analysing their DNA, or the proteins encoded by it.


DNA Comparisons

There is a correlation between the degree of relatedness between individuals/species, and the degree of similarity between their base sequences in DNA. For example, ACTGGAC and ACTGGAT are more similar than ACTGGAC and GCTGGAA. Hence, it may be deduced that the organism possessing the first sequence is more closely related to the second organism, than to the last organism.


One technique which enables scientists to carry out a DNA comparison is called DNA hybridisation. This involves the joining together of DNA sections from 2 species to be compared. These are the steps involved:


1. DNA samples are collected, cut into smaller sections, then heated to 90 degrees.

2. The heat denatures the DNA molecules by breaking the hydrogen bonds within; the strands of DNA separate.


3. The separated strands from the two species are now put together and allowed to cool.


4. Some strands will join back with their original pair; others will join with strands from the other organism to form hybrid DNA.


The temperature at which these strands re-anneal (bond together) is the clue to the genetic relationship between the two organisms. DNA strands which joined back with their original counterpart from the same organism re-anneal at 87 degrees, as they share a lot of base sequences. The hybrid DNA, on the other hand, is formed at a lower temperature. This is because fewer sequences are shared, and so fewer hydrogen bonds are formed which hold the strands together.


The lower the temperature at which hybrid DNA forms between two organisms, the less genetically related they are. This technique has led to a new classification system being used for plants.


Protein (Amino Acid) Comparisons

Proteins are sequences of amino acids. The exact sequence of amino acids found in a protein in an organism may differ from one to another, usually between different species. Whether it differs, and the degree to which it does, suggests how closely related those organisms/species are.


The sequence may be identical, different by 1 amino acid, or different by 50 amino acids. This information is very helpful in building phylogenetic trees, especially as there are so many different proteins which can be analysed to build a complete picture.

Sorry! There are no posts.

Sorry! There are no posts.

Your Reviews

Good topic notes and cool videos. I'll definitely recommend it to my students.

Seema Sehgal AQA Examiner and biology teacher on LinkedIn

I bookmarked the site 

translucent The Student Room

Hi! I have recently finished my first year doing biology at uni and I subscribed to you back when I was doing AQA A levels (glad I don’t live in Wales after watching this vid lol) and you and your website helped me so much. Just wanted to say it’s so nice to see you

Mr Peanutbutter YouTube

Thank you!! Your site is so helpful!

studyaspect YouTube

Just a huge thank you for spending your time helping others. I love your site and I'm seriously very grateful. No word of a lie

Neuron13 The Student Room