Transcript mutations - s3.amazonaws.com

MUTATIONS
Changes in DNA that affect genetic
information. The ultimate source of
variation in individuals.
What Causes Mutations?
 There are two ways in which DNA can
become mutated:
 Mutations can be inherited.
 Parent to child
 Mutations can be acquired.
 Environmental damage due to mutagens
 Mistakes when DNA is copied
What is a mutagen?
 Mutagens are factors that speed up
mutation rate. They include:
 ionising radiation (x-rays, gamma rays
and UV rays).
 Chemicals such as thalidomide,
colchicine, mustard gas, acridine orange.
From studies of mutations three
main facts emerge:
 Mutations can arise spontaneously and are
in no sense directed by the environment.
 Mutations are persistent. They tend to be
transmitted through many generations
without further change.
 The vast majority of mutations confer
disadvantages on the organisms that inherit
them.
Types of mutation:
 If the mutation occurs in the body cells
(is a somatic mutation it cannot be
inherited by offspring).
 If the mutation occurs in the
reproductive cells (gametic cells) and
is not lethal, it can be passed on to
the offspring and become part of the
gene pool.
Somatic mutations




Occur in somatic (body cells)
Affect parts of the body only.
Can be passed on by mitosis when cells divide.
Can result in different cell lines in one organism eg
one brown eye and one blue eye.
 Some cancers result from somatic mutations.
 Can be passed on by asexual reproduction eg
naval oranges, Royal Gala apples.
 Not inheritable and only affect organism in their
lifetime.
Gametic mutations
 Occur only in gametes (ova, sperm/pollen)
 These mutations occur during meiosis or in any
cells from which sex glands are derived i.e. during
embryological development of the sex organs
 Inheritable
 Passed on by meiosis and fertilisation
 If the mutation is survivable and the individual
reproduces, the mutation can lead to new alleles
in the gene pool.
 If advantageous it will become more common in
the gene pool as a result of natural selection.
Gene and chromosome
mutations
 Gene mutations are chemical
changes in individual genes.
 Chromosome mutations involve
changes in the gross structure of
chromosomes.
Gene Mutations
 Point Mutations – changes in
one or a few nucleotides
 Substitution
 THE FAT CAT ATE THE RAT
 THE FAT HAT ATE THE RAT
 Insertion
 THE FAT CAT ATE THE RAT
 THE FAT CAT XLW ATE THE RAT
 Deletion
 THE FAT CAT ATE THE RAT
 THE FAT ATE THE RAT
 Inversion
 THE FAT CAT ATE THE RAT
 THE FAT CAT TEA THE RAT
Gene Mutations
 Frameshift Mutations – shifts
the reading frame of the
genetic message so that the
protein may not be able to
perform its function.
 Insertion
 THE FAT CAT ATE THE RAT
 THE FAT HCA TAT ETH ERA T
 Deletion
H
 THE FAT CAT ATE THE RAT
 TEF ATC ATA TET HER AT
H
Disorders caused by gene
mutations
 Sickle cell anaemia
 You can do some research on this.
Chromosome Mutations
 Changes in number and structure of entire
chromosomes
 Original Chromosome ABC * DEF
 Deletion
AC * DEF
 Duplication
ABBC * DEF
 Inversion
AED * CBF
 Translocation
ABC * JKL
GHI * DEF
Non disjunction
 Failure of chromosomes to
separate during meiosis
 Causes gamete to have too many
or too few chromosomes
 Disorders:
 Down Syndrome – three 21st
chromosomes
 Turner Syndrome – single X chromosome
 Klinefelter’s Syndrome – XXY
chromosomes
Significance of Mutations
• Most are neutral
• Eye color
• Birth marks
• Some are harmful
• Sickle Cell Anaemia
• Down Syndrome
• cancers
• Some are beneficial
• Sickle Cell Anaemia to Malaria
• Immunity to HIV
• You can do some research on the last point
Chromosome Mutations
 Down Syndrome
 Chromosome 21 does not
separate correctly and the
child has 3 chromosome
number 21. This is called
trisomy.
 They have 47 chromosomes
in stead of 46.
 Children with Down
Syndrome develop slower,
may have heart and
stomach illnesses and vary
greatly in their degree of
intelligence.
Chromosome Mutations
 Cri-du-chat
 Deletion of material on 5th
chromosome
 Characterized by the cat-like
cry made by cri-du-chat
babies
 Varied levels of mental
handicaps
Sex Chromosome
Abnormalities
 Klinefelter’s
Syndrome





XXY, XXYY, XXXY
Male
Sterility
Small testicles
Breast enlargement
Sex Chromosome
Abnormalities
 XYY Syndrome
 Normal male traits
 Often tall and thin
 Associated with antisocial and behavioral
problems
Sex Chromosome Mutations
 Turner’s Syndrome
 X or XO - absence of one sex
chromosome.
 Foetuses with 22 pairs of
autosomes and a Y
chromosome never survive to
birth
 Female
 sex organs don't mature at
adolescence
 sterility
 short stature
Sex Chromosome
Mutations
 XXX






Trisomy X
Female
Little or no visible differences
tall stature
learning disabilities
limited fertility
Polyploidy
 Sometimes cell division fails altogether,
resulting in half the gametes having two of
each type of chromosome (being diploid
instead of haploid) and the rest having
none.
 If a diploid gamete fuses with a normal
haploid gamete the resulting individual is
triploid.
 If two diploid gametes fuse the result is
tetraploid.