Mutation Chromosomal Abberation Change in chromosome Chromosomal Arrangements Diseases Causes Effects

2. Definition
Cause of mutations (mutagen)
Mutation frequency
Types of mutations
Chromosome mutations
Point mutations
Gene mutations
Somatic mutations
Kinds of gene mutation

3. “A mutation is a change in
amount or structure of DNA of an
organism.”
A mutation may result in the
change in appearance of a
characteristic in a population.

4.  There are certain physical and
chemical agents which cause an
Inheritable changes in a gene
and thus produce its allele. These
are Called Mutagens.
These are three main categories
of mutagens.

5.  These are high energy radiations
like Alpha, beta, gamma and
cosmic rays. They are called
ionizing b/c they penetrate the
tissues deeply causing ionization
of molecules encountered.

6.  As they penetrate the cells,
electrons are forced to flow out of
molecules, thus stable molecules
and atoms are transferred into free
radicals and reactive ions. These
radiation affect the genetic material
altering the purines and
pyrimidines in the DNA and
resulting in point mutation.

7. These include UV rays.
These cannot ionize the
target tissue. The UV light
effect pyrimidines mainly
to cause a change in DNA.

8.  Certain chemicals such as nitrous
acid hydroxylamine, dimethyl
Sulfonate etc act as mutagens. In
addition a variety of other Chemical
substances including Mustard gas,
caffeine, formaldehyde, certain
components of tobacco & an
increasing no. of drugs, food
preservatives and pesticides also
cause mutation.

9. Mutation occurs randomly and
spontaneously, therefore any
gene can undergoes mutation at
any time. The rates at which
occur also vary from species to
species. The factors that alter
mutation frequency include
temperature, aging and
malnutrition.

10. The work of H.J Miller (1920)
showed that frequency can be
increased by X –rays. Since it
has been shown the rate of
mutation can by increased by
the effect of different
mutagens.

11. CHROMOSOME
MUTATION

12. These changes may involve the
loss or gain of single
chromosomes, a condition
called aneuploidy (2n-1 or 2n+1),
or the increase in whole sets of
chromosomes, a condition
called euploidy (Polyploidy –3n,
4n, 5n & so on).

13.  Zygotes containing less than the
diploid no. of chromosomes
(aneuploidy) usually fail to develop,
but those with polysomic
chromosomes may develop. In most
cases where aneuploidy occurs in
animals, it produces severe
abnormalities. Chromosomal
mutation in human are:

21. Structural change in
chromosomes results from:
a)Deletion and Duplication.
b)Inversion and Translocation.

22. During these changes
the no. of gene loci on
chromosomes is
changed and this has
profound effect on
phenotypes.

23. These changes result in
change in allele sequence of
parental linkage group and
produced recombinant.But
no change loci are lost.These
produced profound effect of
phenotype.

25. Point
Mutation

26.  “A change in nucleotides sequence
of DNA molecule in a particular
region of the chromosome is called
a point mutation”.
 Such a change in the base sequence
of a gene is transmitted to mRNA
during transcription

27.  and may result in a change in the
amino acid sequence of polypeptide
chain produced from it during
translation in ribosome .Since point
mutations are changes in DNA, some
occurs in any type of cell, somatic
(somatic mutation)as well as germ
cells (gene mutation).

29.  Somatic mutation tends to remains
undetected because dominant allele is
present at that locus of
 homologous chromosome. They affect the
organism in which these occur and lost on
the death of an organism. In case of
human mutation may produce cells with
increased rate of growth and division.

31. Gene
Mutation

32. Gene mutations occurring
during gamete formation are
transmitted to all the cells of
the offspring and from one
generation to next therefore
may be significant for the
future of the species.

33.  Most minor gene mutations are
recessive; therefore pass unnoticed
in the phenotype. However, there are
cases where a change in single base
have a profound effect on the
phenotype, for example “sickle cell
anemia” in humans, where mutation
affect only single base in one of
genes involved in the production of
hemoglobin.

35. Kinds of Gene
Mutation

36. “The mutation which arises for no
apparent reason and cause a genetic
alteration is called spontaneous
mutation.”
Spontaneous mutation is a random
and natural. It may occur at any site
of chromosome. It is found that
majority of them produces just a
slight effect and is harmful.

37. The frequency of
spontaneous mutations
is 1-10/million gametes,
but it should not be
underestimated, as any
higher organism
contains thousands of
gene loci.

38. Total mutation rate in
Drosophila indicate in
one generation there is
probability that 5% of the
gamete will contain a
mutation which arose in
that generation time.

39. Overall mutation
frequency per
generation in
Humans is calculated
to be 5% also.

40. “A mutation that is
produced artificially during
experimentation by using
mutagens such as X-rays,
UV rays, etc. is called
induced mutation.”

41. c) Lethal &
Detrimental Mutation

42. “Whose effect is
drastic enough to
eliminate the
individual before
reproductive age”

43. “It may not kill the
individual possessing it,
but the gene is adversely
affected him in some way
and is decreasing his
probability of survival”.

44. Once a gene has mutated to an
allelic form, this mutant gene
will continue to duplicate itself
until it is eliminated together.
However, at times the mutant
gene may mutate back to the
original or wild form of the
gene.

45. This is called back
mutation or reverse
mutation. The frequency
of back mutation is rare
than the forward
mutation, the change from
wild to mutant.