Biology Form 5 Chapter 6 Variation

1. MUTATIONS
Changes in the gene /
chromosomes

2. Genetic Factor that cause variation
GENETIC
MUTATION
SEXUAL
REPRODUCTION
CHROMOSOMAL MUTATION GENE MUTATION
INDEPENDENT
ASSORTMENT
CROSSING
OVER
RANDOM
FERTILISATION
duplication
inversion
translocation
deletion
deletion
insertion
substitution

3. MUTATION
• Mutation: the spontaneous change to the
structure of genes or chromosomes
• Resulting in irreversible & permanent change in
the organism

4. a. Mutation can involve the ENTIRE chromosome
or a SINGLE gene
b. May HELP, HARM, or have LITTLE to no effect
on future generations
o Changes may be SILENT or may cause
phenotypic changes

5. EFFECTS OF MUTATION

7. The causes of mutations
1. DNA fails to copy accurately:-
When a cell divides, it makes a copy of its DNA — and
sometimes the copy is not quite perfect. That small
difference from the original DNA sequence is a mutation.

8.  High energy ionising radiation
- X-rays, gamma rays, ultraviolet
rays.
 Chemical mutagens -
benzene, asbestos, formaldehyde,
pesticide, mustard gas, tar in
tobacco smoke
2. Chemicals / Radiation
These agents cause the DNA to break down.
Mutagens = agents that cause mutation

10. GENE MUTATION

11. Eg of Diseases Caused by Gene
Mutation
 Sickle cell Anemia
 Polydactylism
 Albinism

12. Colour blindness
Mutant gene (recessive gene)
on the X chromosome.
•Not able to differentiate
colours especially green and
red
•More common in males
because male has only one X
chromosome

13. Albinism
The gene for skin colour is
mutated (recessive gene)
•Unable to produce melanin
(black pigment)
•White hair
•Pink eyes and pinkish skin
•Skin is sensitive to sunlight

14. Albinism is caused by an alteration of the
gene that makes the pigment melanin.
ALBINISM not limited to humans

15. Sickle-cell anemia
Mutation in gene that
produce haemoglobin
•Sickle-cell shaped red blood
cells
•Not efficient in transporting
oxygen
•Yellowing of eyes

16. Haemophilia
Mutation in chromosome X
(for blood clotting)
• Have problem in blood
clotting
• May bleed continuously or
for a longer period
• A woman carrier may pass
the disease to a son

17. DNA
4 nucleotide bases:
A, T, G, C.
(adenine, thymine,
guanine, and cytosine. )
The sequence of these
bases encodes instructions
to make amino acids.

18. Sets of three bases that specify
an amino acid - codon
The amino acid that corresponds
to "GCA" - Alanine
20 different amino acids are
synthesized in humans.

19. Gene Mutations
3 types:
1. Base Substitution
2. Base Deletion
3. Base Insertion
Changes in the structure of DNA

20. 1. Base substitution
 one base is replaced by
another.
 ATT/CGC/TTA ATG/CGC/TTA
 Only affects a single amino acid.
 Little effect unless active site of an
enzyme is affected.
 Eg. sickle-cell anemia (caused by
a single amino acid substitution)

21. Analogy
3 letter words because codons are 3 letters
The cat ate the rat.
SUBSTITUTION
Thc cat ate the rat.
May have little effect. You still have the idea like a
typo on a test.
The hat ate the rat.
Changes the thought of the sentence.
The effect depends on where the substitution happens

22. Sickle Cell Hemoglobin
GUG CAC CUG ACU CCU GAG GAG AAG
val his leu thr pro glu glu lys
1 2 3 4 5 6 7 8
GUG CAC CUG ACU CCU GUG GAG AAG
val his leu thr pro val glu lys
1 2 3 4 5 6 7 8
Mutation
(in DNA)
Normal mRNA
Normal protein
Mutant mRNA
Mutant protein
Glutamate (glu), a negatively charged amino acid,
is replaced by valine (val), which has no charge.

23. Sickle Cell Hemoglobin
Significant change
in structure caused
by the single
mutation

24. 2. Base Insertion
 Base insertion means a single base
is added.
 This will affect all subsequent
amino acids in that protein and the
effects are therefore likely to be
severe
 ATT/CCT/GTC ATG/TCC/TGT/C
G

25. Normal DNA: CGA – TGC – ATC
Base Insertion
Mutated DNA: CGA – TAG – CAT – C
Alanine – Threonine – stop
Alanine – Isoleucine – Valine
An adenine was inserted
thereby pushing all the
other bases over a frame.

26. Analogy
Insertion
The cat ate the rat.
The cca tat eth era t.
Inserting the c causes a
FRAMESHIFT
THE SENTENCE NO LONGER
MAKES SENSE!! Insertions may have
huge effects.

27. Gene Mutations
 Huntington’s Disease is caused by
an insertion mutation.
 People with this
disorder have
involuntary movement
and loss of motor
control. They
eventually have
memory loss and
dementia. The
disease is terminal.
Huntington Disease
Located on chromosome 4
First Gene Disease Mapped

28. 3. Base Deletion
 Base deletion means a single base
is omitted.
 This will affect all subsequent
amino acids in that protein and the
effects are therefore likely to be
severe
 ATT/CCT/GTC ATT/CTG/TC

29. Mutated DNA: CGA – TCA- TC
A guanine was deleted,
thereby pushing all the
bases down a frame.
Alanine – Threonine – stop
Alanine – Serine
Base Deletion
Normal DNA: CGA – TGC – ATC

30. Analogy
DELETION
The cat ate the rat.
Thc ata tet her at
FRAMESHIFT
The sentence no longer makes
sense!! Deletions can have huge
effects.

31. CHROMOSOMAL MUTATION

32. CHROMOSOMAL MUTATION
Caused by
•An increase/ decrease in the number of the
chromosomes.
•Changes in the structure of the chromosome.

33. 4 types of chromosomal mutations :
1. deletion
2. inversion
3. duplication
4. translocation
.
CHROMOSOMAL MUTATION

34. 1. Deletion
Deletions are mutations in which a section of
DNA is lost, or deleted.

35. 2. Inversion
Chromosome segment breaks off
Segment flips around backwards
Segment reattaches

36. 3. Duplication
Occurs when a gene sequence is repeated.

37. 4. Translocation
• Involves two chromosomes that aren’t homologous.
• Part of one chromosome is transferred to another
chromosomes

38. Chromosomal Mutation – 4 types

39. A Boy with Cri-du-Chat Syndrome –
a Debilitating Disorder Caused by Chromosome 5 Deletion

40. Cri-du-Chat
- Caused by the Loss of the Short Arm of One Copy of Chromosome 5

41. Deletions - loss of a
chromosomal segment
Eg.
Prader-Willi
Syndrome
Cri du Chat
Syndrome

42. Translocations Lead to a Number of Human Cancers
Burkitt’s lymphoma
- Caused by chromosome
translocation

43.  Video on chromosome
abnormalities

44. 1. Alterations in chromosome number.
Euploid - normal set (2n)
Polyploidy-extra set of the entire genome(3n, 4n etc)
(duplication of the entire set of chromosomes)
Aneuploidy – the number of chromosomes is not
a multiple of the normal haploid number.
(a) Monosomy - one member of a chromosome
pair is missing (2n-1)
(b) Trisomy - one chromosome set consists
of 3 copies of a chromosome
(2n+1)
Chromosomal abnormalities

45.  Occasionally, there is an accident
during Meiosis 1 or Meiosis 2 called
nondisjunction:
How Accidents During Meiosis Can
Alter Chromosome Number
– The members of a chromosome pair fail to
separate during anaphase I or II
– Gametes with an incorrect number of
chromosomes are produced

46. Meiosis I
Nondisjunction
n + 1 n + 1 n - 1 n - 1 n + 1 n - 1 n n
Number of chromosomes
Gametes
Nondisjunction
Meiosis II
(a) Nondisjunction in meiosis I (b) Nondisjunction in meiosis II
NONDISJUNCTION IN MEIOSIS I / MEIOSIS II

47.  The result of nondisjunction
Figure 8.22
Egg
cell
n (normal)
Zygote
2n + 1
n + 1
Sperm
cell
Upon Fertilisation

49. Down Syndrome: An Extra Chromosome 21
–Is also called trisomy 21
Figure 8.19

50. Trisomy 21
or
Downs
Syndrome

51. Down Syndrome Additional chromosome at autosome
21.
•Physical retardation
•Thick neck
•Slanted eyes
•Protuding tongue
•Reduced resistance to diseases

52.  Round face
 flattened nose
bridge
 small, irregular
teeth
 short stature
 heart defects
 A shorter life
span
 mental
retardation
 Underdeveloped
sexual organs
 sterility

53.  The incidence of Down Syndrome
increases with the age of the mother
Figure 8.20

54. KLINEFELTER SYNDROME (44 + XXY)

55. KLINEFELTER
SYNDROME

56. Turner Syndrome (44 + XO)

57. Turner Syndrome (44 + XO)
Constriction
of aorta
(b) A woman with Turner
syndrome (XO)
Poor breast
development
Web of
skin
Under-developed
ovaries
•Infertile , Short, Mentally retarded
•Has no ovaries, Small breasts
•Folded skin on neck
•No menstrual cycle

58. Genetic causes

59. Environmental Factors That
cause Variation
 Climate
 Diet
 Physical accidents
 Temperature
 pH
 Humidity
 Light intensity
 Soil fertility
 Culture
 Lifestyle
PHENOTYPE = GENOTYPE + EFFECTS OF
ENVIRONMENT

66. The Importance of Variation in
the Survival of A Spesies
 Provide necessary adaptation to
help a species survive in an ever
changing environment
 Can withstand severe weather
 Become more resistant to pests
and diseases.

67. Interactions between environmental factors and
genetic factors
 Dark & grey moths
– Biston betularia in England
 Unpolluted environment, lichen
covered tree trunks
- Dark moths not camouflaged.
More easily detected & eaten
by predators.
Dark moth population
decreased.
- Grey moth population

68.  Industrial Revolution
- pollution, soot on trees, lichen
killed
- Dark moths camouflaged. Dark
moth population increased
- Grey moth population
decreased (more obvious to
predator)
 1960, Clean Air Act- air quality
improved.
- Dark moth population decreased
because again more obvious to
predator.
- Grey moth population increased.

69. ~~ENDEND~~

70. Polyploidy
– The number of chromosomes is increased by one
or more sets.
– More common in plants.

71. Searching for Chromosomal Defects - Amniocentesis and Chorionic
Villus Sampling
Many new
techniques for
learning about
individual genes
rather than whole
chromosomes are
available or under
development.

72. Searching for Chromosome and Gene Defects – Pre-Implantation
Genetic Diagnosis (PGD)
Removing a cell for
diagnosis from a human
embryo.
The diagnosis: trisomy
21 (Down syndrome).

73. loss of a chromosomal segment
extra copy of a chromosomal
segment
order of a chromosome
segment has been reversed
chromosomal segment transferred
from one chromosome
to another