CHAPTER 7: MUTATION

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BIO SCORE

CHAPTER 7: MUTATION SUBTOPIC : 7.1

LEARNING OUTCOMES:

7.1 : Mutation classification and types

a) Define mutation

b) Classify mutation

i. Gene / point mutation

ii. Chromosomal mutation

c) State two types of mutation

i. Spontaneous mutation

ii. Induced mutation (e.g exposure to mutagens)

d) Define mutagen

e) State types of mutagen

i. Physical (e.g UV and gamma rays)

ii. Chemical (e.g colchicine and ethidium bromide)

MAIN IDEAS /KEY

POINT EXPLANATION NOTES

Mutation

• A sudden random change in genetic material of a cell that

potentially can cause differ in appearance or behavior from

normal type.

• This alteration can be pass from mother to daughter cell during

cell division.

• If mutation occur in reproductive cell, it may be passed from

parent to offspring.

Classification of

mutation

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MAIN IDEAS /KEY


Types of mutation

• Spontaneous mutation

o A mutation occurring in the absence of mutagens, usually

due to errors in the normal functioning of cellular

enzymes.

o e.g. non-disjunction

• Induced mutation

o A mutation caused by exposure to a mutagen.

Mutagen • A mutagen is anything that changes the genetic material of an

organism / an agent that causes an increase in number of

mutants in a population

• Types of mutagen :

1. Physical mutagen e.g. UV rays, x-rays and gamma rays

2. Chemical mutagen e.g. colchicine and ethidium bromide

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BIO SCORE

CHAPTER 7: MUTATION SUBTOPIC : 7.2

LEARNING OUTCOMES:

7.2 : Gene Mutation

a) Define gene mutation

b) State the four types of gene mutation

c) Explain the four types of gene mutation

i. Base substitution

ii. Base insertion

iii. Base deletion

iv. Based inversion

d) Explain base substitution (e.g. sickle cell anaemia as missense mutation)

e) State the effect of base substitution (missense, nonsense and silent mutation) and base

insertion and deletion (frameshift mutation)

f) Explain base insertion and base deletion as a frameshift mutation.

MAIN IDEAS /KEY


Gene / Point

mutation

• Caused by change in nucleotide sequence of DNA within a

gene

• Result => change in amino acid sequence of polypeptide and

thus different type of protein produced with abnormal function

Types of gene / point

mutation

• Base substitution

• Base insertion

• Base deletion

• Base inversion

Base substitution

● Replacement of one nucleotide and its partner with another pair

of nucleotides

Sickle-cell anaemia. The replacement of T by A nucleotide of the

DNA for the beta chain of haemoglobin changes the codon GAG

(for glutamic acid) to GUG (which encodes valine). Thus the

amino acid in the chain becomes valine instead of glutamic acid.

Base substitution

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MAIN IDEAS /KEY


▪ Characterized by an abnormal form of the blood pigment

haemoglobin

▪ Erythrocyte change from biconcave disc to sickle shape

reducing ability to carry oxygen.

Type of base

substitution

A) Missense mutation

● Mutation that change one codon to another, specifying a

different amino acid.

● Result→ incorporation of the wrong amino acid in polypeptide

chain during translation

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MAIN IDEAS /KEY


B) Nonsense mutation

● Mutation that change a codon into one of the stop codon

(UAA, UGA, UAG).

● Result→ signaling the termination of translation.

C) Silent mutation

● An alteration in a DNA sequence that does not result in an

amino acid change in a polypeptide.

Base Insertion

● Addition of one or a few bases to triplet sequences in DNA.

● Cause frameshift mutation

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MAIN IDEAS /KEY


Base Deletion ● Base deletion is loss of one or a few bases.

● Cause frameshift mutation

Base Inversion ● Base Inversion is change position of two bases.

● Only one amino acid is changed from the normal polypeptide.

● The effect is not critical such as base insertion and base deletion

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MAIN IDEAS /KEY


Frameshift mutation A type of gene mutation where in the addition (insertion) or

deletion of (a number of) nucleotide(s) causes a shift in the

reading frame of the codons in the mRNA, thus, may eventually

lead to the alteration in the amino acid sequence at protein

translation.

Base insertion as a

frameshift mutation

▪ One or more nucleotides are added to the base sequence of the

nucleic acid, which cause the change in the codon reading

frame.

▪ Resulted the changed in the sequence of amino acids starting

the insertion of the base until the end in the abnormal

polypeptide chain.

Base deletion as a

frameshift mutation

▪ One or more nucleotides are deleted in a nucleic acid, resulting

in the alteration of the reading frame of the codon.

▪ This change the sequence of amino acids starting the deletion

of the base until the end. Non function proteins / new proteins

are produced.

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BIO SCORE

CHAPTER 7 : MUTATION SUBTOPIC : 7.3 : Chromosomal mutation

LEARNING OUTCOMES:

a) Define chromosomal mutation

b) State two types chromosomal mutation

i. Changes in chromosomal structure / chromosomal aberration

ii. Changes in chromosomal number

c) Explain changes in chromosomal structure /chromosomal abberation

d) Explain types of chromosomal aberration

i. Translocation

ii. Deletion (segmental deletion e.g cri du chat)

iii. Inversion

iv. Duplication

e) Explain alteration of chromosome number

f) State the types of the alteration (i . aneuploidy ii. euploidy/polyploidy)

g) Explain aneuploidy

h) State aneuploidy effect on autosomal chromosome (Monosomy 21 and Trisomy 21) and sex

chromosome (Klinefelter syndrome and Turner syndrome)

i) Explain autosomal abnormalities and their effects (monosomy and trisomy)

j) Explain sex chromosomal abnormalities

i. Klinfelter syndrome (47, XXY),

ii. Turner syndrome (45, XO)

k) Explain euploidy / polyploid

i. Autopolyploidy

ii. Allopolyploidy

MAIN IDEAS

/KEY POINT EXPLANATION NOTES

Chromosomal

mutation

▪ Changes of chromosome structure (chromosomal abberation) /

alteration of chromosome number

▪ Cause some genetic disorder

Types of

chromosomal

mutation

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MAIN IDEAS


Chromosomal

aberration

Any changes in the normal structure of chromosomes; often results in

physical or mental abnormalities

Types of chromosomal aberration:

▪ Translocation

▪ Deletion (segmental deletion)

▪ Inversion

▪ Duplication

Translocation

▪ A segment of one chromosome is broken off and becomes attached to

another chromosome.

▪ Can be reciprocal translocation and nonreciprocal translocation

▪ Reciprocal translocation - occurs when fragment from non homologous

chromosome changed together

▪ Nonreciprocal translocation

- Intra chromosomal -happen within the same chromosome

- Inter chromosomal -moving one fragment of one chromosome to

non-homologous one

Deletion ▪ The lost of one fragment in chromosome. The leftover will join together.

▪ Deleted chromosome shorter than the normal chromosome and its

missing in certain genes.

▪ Cause abnormality such as Cri du chat syndrome : loss of a small part of

the short arm of chromosome 5.

Inversion ▪ A segment of a chromosome breakdown and turned around 180° within a

chromosome, rearrange the linear gene sequence.

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MAIN IDEAS


Duplication ▪ When a single locus or a large piece of a chromosome is present more

than once in the genome OR occurs when some fragments of the

chromosome breakdown and join with its homologous to form longer

abnormal chromosome which has extra copy genes.

Alteration of

chromosome

number

▪ Due to the changes in the number of chromosomes

▪ Results of errors/non-disjunction occurring during meiosis or during

mitosis

o involved loss or gain of single chromosomes

aneuploidy (2n+1 or 2n-1)

o increased in entire haploid sets of chromosomes

euploidy (3n, 4n, 5n…)

Non – disjunction : an error in meiosis or mitosis in which members of a

pair of homologous chromosomes or a pair of sister chromatids fail to

separate properly from each other

a) Non-disjunction during meiosis

▪ Anaphase I – homologous chromosomes fail to separate

▪ Anaphase II – sister chromatids fail to separate

Fusion of either of these gametes (n-1) or (n+1) with normal haploid

gametes (n) will produces a zygote with an odd number of chromosomes,

(2n-1) or (2n+1)

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MAIN IDEAS


b) Non-disjunction during mitosis – sister chromatids fail to separate

▪ Half the daughter cell produced will have an extra chromosomes, 2n+1

▪ While the other half will have a chromosome missing, 2n-1

Types of

alteration

Aneuploidy

▪ Condition where in which one or more chromosomes are present in

extra copies or are deficient in number.

▪ Total number of chromosomes is not an exact multiple of haploid

number, (n)

eg: (n -1), (2n -1) : deleted

(n +1), (2n +1) : added

Sister chromatids fail to separate

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MAIN IDEAS


▪ Aneuploidy autosomal abnormalities: Monosomy and Trisomy

Aneuploidy effect

on autosomal

chromosome

Monosomy

▪ Condition of diploid cells or organisms lacking in a single chromosome

(2n - 1).

▪ Result of nondisjunction during meiosis

▪ Very rare.

▪ Effects: human embryos with chromosomes missing don't survive to be

born.

▪ Eg: Monosomy 21 for liveborn infants.

Aneuploidy effect

on autosomal

chromosome

Trisomy

▪ Condition of diploid cells or organisms gained a single chromosome

(2n + 1)

• Trisomies can occur with any chromosome, but often result in

miscarriage

▪ Usually the result of nondisjunction during meiosis

Eg: Trisomy 21 / Down syndrome

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MAIN IDEAS


Sex chromosomal

abnormalities

▪ Due to nondisjunction of sex chromosome

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MAIN IDEAS


Klinefelter

syndrome

(2n + 1)

▪ Klinefelter syndrome is a disorder in which males have an extra X

chromosome (XXY) /(2n + 1)

Klinefelter syndrome karyotype

▪ Klinefelter syndrome may occur due to nondisjunction during meiosis I

(oogenesis or spermatogenesis) or meiosis II (oogenesis)

• Gender: Male

• Characteristics: sterility, small testicles, breast enlargement, narrow

shoulders

Turner syndrome

(2n-1) /

Monosomy X (2n-

1)

▪ Turner syndrome is a disorder that affects females. Individuals with

this syndrome, also called monosomy X, have a genotype of only one X

chromosome (XO) /(2n-1)

Turner syndrome karyotype

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MAIN IDEAS


▪ Turner syndrome may occur due to nondisjunction during meiosis I or

meiosis II of oogenesis or spermatogenesis.

• Genotype: XO

• Gender: female

• Characteristic:

- Short stature

- Webbed neck

- Triangular face

Euploidy /

Polyploidy

▪ Condition where in which one or more chromosomes are present in

extra copies or are deficient in number eg: triploid (3n), tetraploid (4n).

Caused by nondisjunction on whole sets of chromosome

▪ Polyploids can originate:

● Spontaneuosly or artificially induced using colchicine (mutagen)

● Inhibits spindle formation in mitosis or meiosis

● Chomosomes do not separate and move to opposite poles

● Doubling in chromosomes set

● Divided into:

• Autopolyploidy

• Allopolyploidy

Autopolyploidy Condition of a cell, nucleus or organism in which there are three or more

sets of chromosomes within the same species

• Non disjunction on whole sets of chromosomes happen in same

plants species.

• Non disjunction produces diploid gametes (2n).

• Diploid gametes can fertilize itself to form tetraploid (4n)

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MAIN IDEAS


Allopolyploidy

▪ Condition of a cell, nucleus or organism in which there are three or more

sets of chromosomes derived from closely related different species /

two different species.

▪ Zygote/offspring produce known as F1 hybrids

▪ Hybrids usually sterile because do not have homologous chromosomes

to pair up during meiosis

● no gamete can be produce

● sexual reproduction inhibited

● hybrids reproduce vegetatively (asexually)

▪ Sterile hybrid becomes fertile if doubling of chromosomes occur by

non-disjunction.

● Homologous chromosomes pairing is now possible.

● Fertile gamete can be produce.

● New plant arise and can reproduce sexually

CHAPTER 7: MUTATION

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