Mutation

  1. MUTATION.                                                                                                                                   Is a sudden change in the gene or chromosome structure or the number of chromosomes In an organism (sudden change in the genetic make up of an organism) and such a change may lead to new characters appearing in organisms or the formation of a complete new specie of organisms. It may have undesirable effects especially on humans or it may have benefits to man e.g. production of crops with desirable characteristics. It can occur naturally but there are factors which can induce mutation and these include;

Use of chemicals e.g. mustard gas and colchicines.

Use of radioactive substances e.g. X rays, ultra violet radiations, etc.

Types of Mutation.

It’s grouped according to whether the change has occurred in the gene or the chromosome.

Therefore, there are two types of mutation;

Gene mutation and Chromosomal mutation.                                                                                           Chromosomal mutation is more common than gene mutation. The later is mainly concerned with D.N.A and it’s not common because D.N.A is very stable and can not easily be changed.                                                                                                               Chromosomal mutation;                                                                                                                       

Causes.

Deletion: vital genetic information may be deleted from the chromosome

A
B
C
D
E
A
B
C
D

 

Translocation: Part of the chromosome with vital information breaks off and joins another.

 

A
B
C
D
E
  1.                 Part F joins
A
B
C
D
E
F

 

Inversion: Genetic message is reversed or when a section of chromosome breaks off and turns through 180o and attaches its self.

 

 

 

A
 B
C
D
E
E
D
C
B
A

Duplication: it’s the doubling of the genetic information

 

A A
B B
 C C
D D
  A
  B
C
D

 

EXAMPLES OF CHARACTERISTICS RESULTING FROM MUTATION IN MAN

Albinism: This is a result of the recessive mutant gene which prevents formation of normal skin colour/pigmentation.

Sickle cell anaemia: Presence of a recessive gene responsible for formation of abnormal haemoglobin.

Mongolism: There is an extra chromosome in the cells of mongo people. They have no resistance to diseases and therefore hardly survive. They are mentally retarded and this condition is known as Down’s syndrome.

Turner’s syndrome: is when either the X chromosome or the Y chromosome is missing in the gametes and gives the genetic constitution of XO. They are normally females who are infertile and can not get pregnant. They have under developed sex characteristics.

Achondroplasia: is dwarfism due to a dominant mutant gene. It’s a rear condition since most homozygotes die off.

Cystis fibrisis: Mucus containing cells of the pancreas and other 0rgans do not function normally. Its due to a recessive mutant gene.

XXY: is acondition which occurs when a Y sperm fertilizes an XX diploid egg. Its referred to as Klinefelter’s syndrome. Externally, this person is a male but can not produce sperms (sterile) and has some feminine features.

XXX : is a female who is mentally retarded.

Its now possible to detect that the baby will be a mutant with extra/less chromosomes before its born by a process known as amniocentesis. Some amniotic fluid is examined since it has cells from which are peeled off from the skin of the embryo. Such cells will show any defects in the chromosomes. In case of mutant signs, the pregnancy may be terminated by abortion.

Haemophilia: Is as a result of a mutant recessive gene carried on the X chromosome which prevents easy clotting of blood from even a simple wound.

Other organisms

Resistance of mutant mosquitoes to DDT

Resistance of mutant bacteria to penicillin

Polyploidy

When a cell undergoes meiosis, complete separation of chromosomes may fail. This means that some gametes are diploid and others are empty. There at fertilization one gets conditions like, i) 2n + n = 3n (triploid)

ii) 2n + 2n = 4n (tetraploid)

After fertilization, in formation of new body cells by mitosis, the chromosome set doubles meaning that the cells will be tetraploid. Its common in plants and results into varieties with desirable characteristics eg resistance to diseases, resistance to bad environmental conditions, varieties which give off very high yield and varieties which mature fast.

Advertisements

One response to “Mutation

  1. Basil thompson

    thank you for the great assistance,,,

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s