Page 174 - Big Ideas Year 10 sciPAD 2025

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174 SCIPAD - BIG IDEAS - BOOK 2
THE BASIS OF HEREDITY
Producing New Alleles - Mutations
In the wild, budgerigars are green. However, in captivity bird breeders
have managed to produce a vast range of colours. If their feather
colour is controlled by a gene, then how are these new different
versions of the gene (alleles) produced?
The instructions for making an organism are contained in the
sequence of bases found in their DNA. Sometimes, during
the copying of this DNA (to make new cells), or during the
production of sex cells (to make a new organism), a change
can occur in the base sequence. Scientists call these changes
mutations.
The word mutation comes from a Latin word, ‘mutatio’ which
means ‘change’.
Most organisms are carrying mutations – including yourself. In
fact, it is suggested that each of us has up to 30 mutations in
our bodies at any one time.
Mutations can be caused by ultra-violet light (from the sun),
chemicals (such as those found in cigarettes), diet (fatty foods,
etc.), or exposure to radiation (from x-rays, or radioactive materials, etc). Anything that causes a
mutation is called a mutagen.
‘Mutation’ sounds like a word that means only bad things. However, mutations may be neutral or
silent (i.e. they have no observable effect on an organism). Some mutations may be harmful and
may effect the survival of the organism. One of the most common harmful mutations in humans
is cancer. Cancer is caused by a mutation which makes cells divide and grow at an abnormally
fast rate. As the cancerous cells continue to grow and divide they produce a mass of tissue called
a tumour.
Occasionally, a beneficial mutation may produce an allele that gives the organism a survival
advantage over other members of its species. This may mean the organism is better adapted to
its surroundings, improving its chances of survival. This organism is more likely to have offspring that
will inherit the beneficial allele. Scientists call this ‘natural selection’.
1. Define the term mutation. 

2. Where does the term mutation come from? 

3. (a) Define the term mutagen. 

(b) Give three examples of mutagens (i) 
(ii) 
(iii) 
(c) Exposure to mutagens can lead to a particular disease in humans. Name this
disease. 
4. Use the word list provided to complete the following paragraph.
offspring - alleles - survival - mutations - survive
may produce alternative forms of a gene, called .
A new allele may give an organism a advantage, meaning it
is better able to and out-compete other organisms. This means
the organism is likely to produce more that will inherit the
new allele.
White peacocks are not albinos. They
actually have a genetic mutation
known as Leucism, which causes the
lack of pigments in the plumage.
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