Download L7 gene_mutations

Genetic diversity and adaptation
Gene Mutations
Gene mutation
Learning Objective:
In order to be successful in this lesson you must
be able to:
interpret base sequences to identify gene mutations and their impact
Gene mutation
explain what a
gene mutation
is and how they
arise
explain what
is meant by a
deletion and
substitution
mutation, and
the potential
consequences
of each (linked
to protein
structure)
PROGRESS
interpret base
sequences to
identify gene
mutations and
their impact
What is a Mutation?
• A mutation is any change in the amount or structure of the
DNA of an organism.
KEY POINT:
If this occurs in somatic (body) cells, the change cannot be
inherited. Only mutations in the DNA within gametes can be
passed on to the next generation.
Causes of Mutations
• Mutations occur naturally and at random.
• However, mutagens are environmental factors that increase
rate of mutation.
High-energy
particles
High-energy particles
from radioactive
substances
High energy
radiation
UV/ x rays/
gamma rays
Mutagenic chemicals
Carcinogenic
substances such as tar
and asbestos
Gene Mutations
Gene Mutations
There are 3 types:
1. Substitution
One nucleotide is replaced by another with a different base.
2. Addition
An extra nucleotide is added so an extra base is added to the
sequence.
3. Deletion
One nucleotide is removed.
Substitutions
Substitutions only affect one codon in a sequence of genetic
material. They therefore only affect the outcome of a single
amino acid.
G C T A G A
T A T A C G T
Arginine
Serine
Tyrosine
Tyrosine
Alanine
The above animation is a worst case scenario when it comes to
substitution mutations.
What are the potential consequences of this gene mutation?
Why might a substitution mutation not have an effect on
protein shape at all?
Deletion of bases
What is meant by a deletion mutation?
Model an example of a deletion mutation?
Describe the potential consequences of a deletion mutation?
Extension questions:
Which type of gene mutation is likely to be the most damaging and why?
A student wrote that UV light increased the likelihood of mutations in the
protein that the cell made. Why is this not correct?
Crack the code!!
Activity:
1.
2.
3.
4.
5.
6.
Choose A, T, C or G to put into each of the spaces on the DNA sequence
Transcribe the DNA into mRNA, remembering to use Uracil instead of
Thymine.
Find the start codon
Decode the codons one by one, writing each amino acid’s name directly
below each codon
Keep going until you reach a stop codon
Count how many amino acids are in your protein
Keep everything lined up on the page (using the stripes) as this will make
everything much easier when you compare your resultant proteins.
Effects of mutations
•XAT:
•GGX:
•ATX:
A gives Leu, T gives Ile, C gives Val, G gives Leu
Everything gives Proline
A/G give Tyr, T/C give STOP (shortening the resultant protein)
What would have
happened if there
was a deletion
mutation? Discuss
the havoc these
mutations can wreak
compared to single
point mutations.
Use your textbook to
help:
Homework
• explain what a non-disjunction event is and how they occur
• compare and contrast gene and chromosomal mutations.
Briefly explain non-disjunction as a mechanism of chromosomal mutations
http://www.sumanasinc.com/webcontent/animations/content/mistakesmeiosis
/mistakesmeiosis.swf
Explain the possible consequences of a non-disjunction event in animals.
For example, briefly research non-disjunction events in humans e.g. Down’s syndrome,
Turner’s syndrome
Use your textbook to
help:
Homework
• explain what a non-disjunction event is and how they occur
• compare and contrast gene and chromosomal mutations.
Briefly explain non-disjunction as a mechanism of chromosomal mutations
http://www.sumanasinc.com/webcontent/animations/content/mistakesmeiosis
/mistakesmeiosis.swf
Explain the possible consequences of a non-disjunction event in animals.
For example, briefly research non-disjunction events in humans e.g. Down’s syndrome,
Turner’s syndrome