Mutation

12.3

Mutation

Definition of Mutation

A spontaneous and random change of genetic material, namely DNA of the cell in an organism.

Mutagen

A substance which causes mutation or increases the mutation rate to a dangerous level.

Process of Mutation

Mutation occurs spontaneously in natural conditions.

Mutant

New genetic material produced by mutation is called a mutant.
A mutant can exist as mutant gene, mutant cell, mutant organelle or mutant individual.

Types of Mutagen

Physical Agents

Ultraviolet from the sun.
Ionising rays such as X-ray, alpha ray and beta ray.

Chemical Agents

Carcinogen in cigarette smoke.
Food preservatives.
Formaldehyde.
Benzene.

Biological Agents

Virus.
Bacteria.

Types of Mutations

Gene Mutation

Gene mutations occur when there is a change in the nucleotide base sequence in a gene.
Gene mutations are also known as point mutations.
These changes alter the genetic code used for amino acid synthesis.
As a result, the structure of the produced protein changes and the new protein synthesized is unable to function.
Gene mutations occur through base replacement, base deletion and base insertion.
Gene mutations cause genetic diseases such as thalassemia, cystic fibrosis, sickle cell anemia, albinism and hemophilia.
- Sickle cell anemia:
  - Sickle cell anaemia is caused by a gene responsible for the synthesis of haemoglobin.
  - The red blood cells of a patient are in the shape of a crescent.
  - This is because the red blood cells are not properly formed.
  - Some red blood cells are normal whereas the rest are crescent shape.
- Albinism:
  - An individual who experiences albinism is an albino.
  - Albinism is due to the mutation of a gene which is responsible for producing pigments of skin, hair and eyes.
  - Hence, the pigments are not produced in the albino.
Example of genetic disease is as shown below:

Types of Gene Mutation	Examples of Disease
Base substituition	Sickle cell anaemia
Base insertion	Cystic fibrosis
Base deletion	Thalasemia

Chromosomal Mutation

Chromosomal mutations involve changes in the structure of chromosomes or changes in the number of chromosomes.
Chromosomal mutations can cause characteristic changes in an organism.
Changes in chromosomal structure involve changes in the arrangement of genes on a chromosome.
Changes in the structure of chromosomes cause abnormalities in those chromosomes.
This condition of abnormality is called chromosomal aberration.
Types of chromosomal aberration:
- Deletion:
  - A part or a segment of chromosome is deleted or lost (loss of a few genes).
- DuplicationPenggandaan:
  - A part of a chromosome is copied which causes repetition of gene sequence.
- Inversion:
  - A segment of chromosome is reversed end to end at 180o then rejoin (change in DNA sequence of chromosome).
- Translocation:
  - Part of the chromosome is cut, then join to another non-homologous chromosome.
A change in chromosomal number causes a diploid organism to lose one or more chromosomes, or gain one or more chromosomes.
The change occurs when homologous chromosomes fail to separate during anaphase I in meiosis or sister-chromatids fail to separate during anaphase II in meiosis.
This is probably because the normal spindle fibres fail to form during meiosis.
Abnormality in the number of chromosomes can be due to nondisjunction during spermatogenesis or oogenesis.
Fertilisation that involves abnormal gametes will produce a zygote that develops into an individual with abnormal characteristics.
The individual experiences change in phenotype

Characteristics of Diseases Caused by Chromosome Mutation
Abnormalities in Autosomes
Diseases	Chromosome Number	Characteristics of Diseases
Down Syndrome	(2n + 1) = 47. Has three number 21 chromosomes.	An individual (male or female) has slant eyes, flat nose, protruding tongue, broad forehead and is usually mentally retarded.
Cri du chat syndrome	The structure of chromosome changes due to a partial deletion on the short arm of chromosome number 5.	The cry of affected infants is similar to that of a meowing kitten. Affected individual shows delayed development with mental and physical retardation. Most patients die during childhood.
Abnormalities in Sex Chromosomes
Klinefelter Syndrome	(2n + 1) = 47 44 + XXY	A sterile man with small testes that fail to produce sperms. Possesses voice and chest similar to those of a woman. Has long legs and hands
Jacob Syndrome	(2n + 1) = 47 44 + XXY	Male who is taller than normal and has problem with pimples on his face. Slow in acquiring speech and has learning disability. Possesses weak muscles (hypotonia).
Turner Syndrome	(2n + 1) = 45 44 + XO	Sterile female with lack of secondary female characteristics, undeveloped breasts and ovaries. Weblike neck and low IQ.

Mutation of Somatic Cells and Gametes

Mutation can occur in somatic cells and gametes to produce variation in a population.
The table below shows the differences between mutation in somatic cells and gametes.

Mutation in Somatic Cells	Mutation in Gametes
Involves somatic cells such as skin cell and eye cell.	Involves germ cell that produces gamete (secondary oocyte or sperm).
Cannot be inherited by the next generation.	Can be inherited by the next generation.
Disease is present only in the individual with the mutation.	Disease is present in the individual with the mutation and is also inherited by his/her descendants.
Example: Disease related to nervous system.	Example: All inherited diseases such as thalassemia.

Mutation

12.3

Mutation

Definition of Mutation

A spontaneous and random change of genetic material, namely DNA of the cell in an organism.

Mutagen

A substance which causes mutation or increases the mutation rate to a dangerous level.

Process of Mutation

Mutation occurs spontaneously in natural conditions.

Mutant

New genetic material produced by mutation is called a mutant.
A mutant can exist as mutant gene, mutant cell, mutant organelle or mutant individual.

Types of Mutagen

Physical Agents

Ultraviolet from the sun.
Ionising rays such as X-ray, alpha ray and beta ray.

Chemical Agents

Carcinogen in cigarette smoke.
Food preservatives.
Formaldehyde.
Benzene.

Biological Agents

Virus.
Bacteria.

Types of Mutations

Gene Mutation

Gene mutations occur when there is a change in the nucleotide base sequence in a gene.
Gene mutations are also known as point mutations.
These changes alter the genetic code used for amino acid synthesis.
As a result, the structure of the produced protein changes and the new protein synthesized is unable to function.
Gene mutations occur through base replacement, base deletion and base insertion.
Gene mutations cause genetic diseases such as thalassemia, cystic fibrosis, sickle cell anemia, albinism and hemophilia.
- Sickle cell anemia:
  - Sickle cell anaemia is caused by a gene responsible for the synthesis of haemoglobin.
  - The red blood cells of a patient are in the shape of a crescent.
  - This is because the red blood cells are not properly formed.
  - Some red blood cells are normal whereas the rest are crescent shape.
- Albinism:
  - An individual who experiences albinism is an albino.
  - Albinism is due to the mutation of a gene which is responsible for producing pigments of skin, hair and eyes.
  - Hence, the pigments are not produced in the albino.
Example of genetic disease is as shown below:

Types of Gene Mutation	Examples of Disease
Base substituition	Sickle cell anaemia
Base insertion	Cystic fibrosis
Base deletion	Thalasemia

Chromosomal Mutation

Chromosomal mutations involve changes in the structure of chromosomes or changes in the number of chromosomes.
Chromosomal mutations can cause characteristic changes in an organism.
Changes in chromosomal structure involve changes in the arrangement of genes on a chromosome.
Changes in the structure of chromosomes cause abnormalities in those chromosomes.
This condition of abnormality is called chromosomal aberration.
Types of chromosomal aberration:
- Deletion:
  - A part or a segment of chromosome is deleted or lost (loss of a few genes).
- DuplicationPenggandaan:
  - A part of a chromosome is copied which causes repetition of gene sequence.
- Inversion:
  - A segment of chromosome is reversed end to end at 180o then rejoin (change in DNA sequence of chromosome).
- Translocation:
  - Part of the chromosome is cut, then join to another non-homologous chromosome.
A change in chromosomal number causes a diploid organism to lose one or more chromosomes, or gain one or more chromosomes.
The change occurs when homologous chromosomes fail to separate during anaphase I in meiosis or sister-chromatids fail to separate during anaphase II in meiosis.
This is probably because the normal spindle fibres fail to form during meiosis.
Abnormality in the number of chromosomes can be due to nondisjunction during spermatogenesis or oogenesis.
Fertilisation that involves abnormal gametes will produce a zygote that develops into an individual with abnormal characteristics.
The individual experiences change in phenotype

Characteristics of Diseases Caused by Chromosome Mutation
Abnormalities in Autosomes
Diseases	Chromosome Number	Characteristics of Diseases
Down Syndrome	(2n + 1) = 47. Has three number 21 chromosomes.	An individual (male or female) has slant eyes, flat nose, protruding tongue, broad forehead and is usually mentally retarded.
Cri du chat syndrome	The structure of chromosome changes due to a partial deletion on the short arm of chromosome number 5.	The cry of affected infants is similar to that of a meowing kitten. Affected individual shows delayed development with mental and physical retardation. Most patients die during childhood.
Abnormalities in Sex Chromosomes
Klinefelter Syndrome	(2n + 1) = 47 44 + XXY	A sterile man with small testes that fail to produce sperms. Possesses voice and chest similar to those of a woman. Has long legs and hands
Jacob Syndrome	(2n + 1) = 47 44 + XXY	Male who is taller than normal and has problem with pimples on his face. Slow in acquiring speech and has learning disability. Possesses weak muscles (hypotonia).
Turner Syndrome	(2n + 1) = 45 44 + XO	Sterile female with lack of secondary female characteristics, undeveloped breasts and ovaries. Weblike neck and low IQ.

Mutation of Somatic Cells and Gametes

Mutation can occur in somatic cells and gametes to produce variation in a population.
The table below shows the differences between mutation in somatic cells and gametes.

Mutation in Somatic Cells	Mutation in Gametes
Involves somatic cells such as skin cell and eye cell.	Involves germ cell that produces gamete (secondary oocyte or sperm).
Cannot be inherited by the next generation.	Can be inherited by the next generation.
Disease is present only in the individual with the mutation.	Disease is present in the individual with the mutation and is also inherited by his/her descendants.
Example: Disease related to nervous system.	Example: All inherited diseases such as thalassemia.

Mutation

Mutation

Chapter : Variation

Topic : Mutation

Related notes