Transcript Mechanisms of genetic changex

Genetic Change
DOT Point
Distinguish between mutations of chromosomes
Rearrangements
The are 4 types of rearrangement:
1. Deletion – where part of a chromosome breaks off and a
gene is lost from the chromosome, e.g. Chit-du-Chat
syndrome where a deletion from Chromosome 5 occurs
2. Duplication – where the same section of a chromosome is
copied or occurs twice. May be copied on to the
homologous chromosome
3. Inversion – order of genes is reversed. Occurs due to
breaking and re-joining in opposite directions
4. Translocation – part of the chromosome breaks off and
attaches to another, e.g. breakages in 21 can cause down
syndrome
Changes in chromosome number
This can occur during meiosis if homologous chromosomes
don’t separate.
It is called non-disjunction and results in some gametes with
extra or less chromosomes.
Trisomy or triplication – There is an extra copy of one
chromosome, e.g. Down syndrome is caused by trisomy-21where
there are 3 number 21 chromosomes.
Polyploidy – When meiosis fails completely in one parent and
an offspring inherits a full extra set of chromosomes (3n). This is
common in plants, but fatal to humans
Mutations of genes
There are 2 types of mutagens:
1. High energy radiation e.g. gamma, x-rays and
UV
2. Chemical mutagens e.g. hydrocarbons in
cigarette smoke and many industrial chemicals
Mutations of genes
Base substitution – Occurs when one base is
replaced by another. The polypeptide will have
one wrong amino acid.
Frame Shift – Extra bases are added or deleted
from a gene and will affect the whole base
sequence, making a completely different
and usually non-functional polypeptide.
Process and analyse information from secondary sources to describe the
effect on one named and described genetic mutation on human health
The cause of Down Syndrome
trisomy-21 when there is an additional copy of number
21 chromosome in the individual
can be result of non-disjunction when a gamete with two
copies of number 21 chromosome (since homologous
chromosome pair did not separate during meiosis) fuses
with a normal gamete
can be result of translocation of part of chromosome 21
to another chromosome, usually chromosome 14 or 15
Process and analyse information from secondary sources to describe the
effect on one named and described genetic mutation on human health
The effect of Down Syndrome
lower than average mental ability
almond shaped eyes, shorter limbs, speech impairment,
enlarged tongue, high risk of heart failure
Process and analyse information from secondary sources to describe the
effect on one named and described genetic mutation on human health
The impact of Down Syndrome
reduced mental capacity may be a limiting factor on
development on individual in respect to social
development, schooling and workforce - restrict
opportunities
physiotherapy needed as they have weakened muscles,
shorter arms and legs
increased risk of several diseases such as cardiovascular
failure
Outline the ability of DNA to repair itself
Mutations are quite common - caused by chemical
mutagens, radiation and other mutagens - and so DNA
needs to be able to repair itself to ensure no abnormal
proteins are produced.
Over 130 genes are responsible for repairing DNA
Copying errors are repaired by enzymes such as DNA
polymerase which fixes incorrect bases based on the
undamaged strand.
DNA repair genes stop the cell cycle while enzymes
replace and repair damaged regions or bases
Outline the ability of DNA to repair itself
The DNA can be repaired in three main ways:
Damage reversal – Enzymes restore structure without
breaking backbone2)
Damage removal – who damaged section is cut out (e.g. by
glycosylase enzymes) and the correct bases are put back in
Damage tolerance – where a method is found to cope with
the damage, e.g. leaving a gap where the damage is when
replicating, although this can be dangerous if the cell divides
Not fixing damaged genes would lead to permanent
mutations that can cause cancer and malfunction of cells
Describe the way in which transposable genetic elements
operate and discuss their impact on the genome
Transposable genetic elements/transposons/jumping genes are
sections of DNA that are not fixed and can move around among
chromosomes.
Code for an enzyme that allows the movement or ‘jumping’
between chromosomes
In bacteria, transposons within plasmids can move between
bacteria. This means that antibiotic resistance is not simply
transferred by asexual reproduction, but it can spread to the
genome of other bacteria
The impact on humans is not yet clear, although transposons
could be inserted into another gene, causing mutation
Distinguish between germ line and somatic
mutations in terms of their effect on species
Germ line – cells which produce gametes
Mutations which affect sperm or ova
Passed onto offspring
Can have an effect on whole populations are it
is passed on. Provides a source of variation
which can either be continued due to natural
selection
Distinguish between germ line and somatic
mutations in terms of their effect on species
Somatic – body cells
When mutation occurs, DNA is altered as with
germ line cells and so gene expression is altered
The different is somatic cells are not passed on
to the next generation so affect only one
organism