Download Mutations ATAR

Lesson starter
Write down three differences
between translation and transcription
How can mutations
affect phenotype
(physical appearance)
and genotype?
Are mutations a good
or bad thing?
Learning objectives:
Mutations
• State that mutations cause changes to
the sequence of nucleotides in DNA
molecules
• Explain how the mutations can have
beneficial, neutral or harmful effects
on the way a protein functions
The Contribution of Alleles to Phenotypic
Variation

Variation between members of the same species is
described as intraspecific variation

Phenotypic variation describes the outward physical
appearance as a result of genetic variation

Examples of phenotypic variation:




Morphological
Biochemical
Physiological
Behavioural
The Contribution of Alleles to Phenotypic
Variation

Different forms of the same gene are called alleles

Chromosomes are stacks of genes and we get two sets;
one from each parent. Each homologous pair of
chromosomes contains slightly different genes. E.g.
brown eyes vs blue eyes

The genotype of an organism will determine the
phenotype (genes determine physical appearance)
Variation

Variation in offspring is essential for life to
continue.

Variation is created by:



Meiosis (crossing over of portions of chromosomes,
random assortment of chromosomes at metaphase)
Fertilisation (egg and sperm meet totally at random)
Mutations
Mutations are the source of novel genetic
variation
Germline cell mutation

Mutations in gametes

Potentially can be inherited

Fetus can be spontaneously
aborted due to mutation

May result in congenital
abnormalities
Somatic cell mutation
 Only affects daughter
cells of mutated cell

All other cells lack
mutation

Cancer is an example
Mutations

A mutation is a change in the structure or quantity of an organism’s
genetic material.

A gene mutation is a change in one or more nucleotides in a strand
of DNA

A chromosome mutation is a change to the structure, such as
deletion, inversion or translocation, or a change to the number of
chromosomes in a nucleus

Mutations can vary from a small change in DNA or a gene or be a
large change in chromosome structure or number
DNA mutations – point mutations

Substitution: one nucleotide is replaced by
another with a different base

Inversion: nucleotides change position with
each other
DNA mutations – frameshift mutations

Deletion: one nucleotide is removed from the
chain and the chain joins up again

Insertion: one extra nucleotide is inserted
into the chain
Types of Mutation

Point mutations: these are only minor mutations
that will affect the organism only slightly or not at all



Substitution
Inversion
Frameshift mutations: these lead to major changes
as large portions of DNA are misread


Insertion
Deletion
Remember SIDI for mutations! Substitution, Inversion, Deletion,
Insertion
http://www.bbc.co.uk/scotland/education/bitesize/higher/biology/genetics_adaptation/mutations1
_rev.shtml
Frameshift Mutation

Inserting or deleting one or more
nucleotides

Changes the “reading frame” like
changing a sentence

Proteins built incorrectly
Frameshift Mutation

Original:


The fat cat ate the wee rat.
Frame Shift (“a” added):
 The fat caa tet hew eer at.
Amino Acid Sequence
Changed
Deletion – no G
Substitution – A for G
Insertion – extra C
Inversion – bases
swapped around
Mini Plenary
Framshift mutations result in minor changes to
DNA
True
False
Mini Plenary
Point mutations only cause minor effects to
changes in DNA
True
False
Mini Plenary
Insertion mutations add an extra amino acid to
the sequence
True
False
Mini Plenary
Mutations can affect genes or chromosomes
True
False
Examples of Mutations

Sickle cell anaemia

Cystic Fibrosis

Protooncogenes in cancer
Frequency of Mutations & Mutagenic Agents

Without external influences, mutations occur
randomly and spontaneously

Mutations of this kind are very rare as most mutant
genes are recessive.

A person would have to be homozygous to display
the mutant trait in their phenotype

Mutagenic agents can increase the rate at which
mutations occur


Mustard gas
Types of radiation e.g. gamma rays, X-rays and UV light
Chromosome Mutation
Animation
Gene Mutations

Change in the nucleotide sequence
of a gene

May only involve a single nucleotide

May be due to copying errors,
chemicals, viruses, etc.
Point Mutation

Sickle Cell disease is
the result of one
nucleotide substitution

Occurs in the
hemoglobin gene
Gene Mutation Animation
Cell division

Cell division is tightly
controlled by genes, there
are two types involved in
this


Tumour suppressor genes –
that slow cell division
Proto-0ncogenes - that
stimulate cell division
These ensure that cells divide at a fairly constant rate, and those
cells that are worn out or dead are replaced
Proto oncogenes

These are normally only switched ‘on’ when
growth factors are detected by protein
receptors on the cell surface membrane.
These cause relay proteins in the cytoplasm
to switch these genes on.
Oncogenes

A mutation can cause proto oncogenes to mutate into
oncogenes

This is when these genes are permanently switched
on, even in the absence of growth factors that would
normally stimulate appropriate cell division


The receptor on the cell surface membrane could be permanently
activated
A growth factor is produced in excessive amounts
Tumour Suppressor Genes



These inhibit cell division
This maintains normal cell division and
prevents tumours from developing
If these genes become inactivated a tumour
can develop
Describing how mutations happen

Study the diagrams below. Using these
diagrams to help you, describe the mutation that
has occurred and the consequence it has for the
protein formed.
Sickle cell anaemia
Cystic Fibrosis
Describing how mutations happen

Sickle cell anaemia: a result of a point
mutation on codon 6 of the gene for the beta
polypeptide chain of haemoglobin.

CF: a deletion deleting ONE amino acid out
of 1480 in a polypeptide chain
How can mutations
affect phenotype
(physical appearance)
and genotype?
Are mutations a good
or bad thing?