Frameshift mutations

1. FRAME SHIFT MUTATIONS
Submitted By :
Submitted To: Amit Kumar
Dr. Ruchi Seth Mam
Reg.No.:15BBIC018

2. FRAME SHIFT MUTATIONS
> A frame shift mutations also called a framing error or reading frame shift.
>It is a genetic mutations caused by the addition or deletion of nitrogenous base
in DNA or MRNA are known as frame shift mutations.
>Because these shifts the reading frame of codons from the site of change
onward on deletion may be neutralized by one addition or vice versa.

3. TYPES OF FRAME SHIFT MUTATIONS
There are two types of frame shift mutations
1.Deletions mutations:- These mutations are caused due to the loss or deletion of
one or more nucleotides.
2.Insertion mutations: These mutations are caused by the addition of one or more
extra nucleotides in a DNA molecule at one or more places.

4. MECHANISM OF ORIGIN OF FRAME SHIFT
MUTATIONS
>Acridine dyes have been found to cause deletion or insertion of a single base
pair.Acridines like 5-aminoacridine and proflavin become intecalated between two
adjacent purinces and increase the distance between them from 3.4A to 6.8A.At
the time of DNA replication,either a nitrogenous base pair is introduced in the gap
or a nitrogenous base pair is lost.
>Frame shift mutations caused by the deletions are also introduced by the
removal of ethylated bases.

5. MUTATIONS DUE TO CHROMOSOME
ABERRATION
>The occasional breaks in the chromosomes and fusion of the broken ends
causes many changes in the chromosomes called chromosomal aberrations.
>Likewise chromosomal aberrrations are also the kinds of mutations produced as
a result of segmental change in the chromosome.
>These were observed of C.B Bridges and A.H Sturtevant in Drosophila as early as
1923.The Breaks may occur either in single chromosome,in a pair or in non-
homologous chromosomes.

6. >The structural changes in the chromosomes are of various types these changes
may involve either the loss of broken fragments of chromosome or addition of
same fragment.
>In more complicated changes segments get exchanged between two different
chromosomes being termed as translocatons.Thus,in brief stuctural changes may
be of following types:
1.Translocations.
2.Deletions.
3.Duplications(repeats).
4.Inversions

7. 1.Translocations:- Translocations is the transfer of a portion of one chromosome to
a non-homologous chromosome.At present,a variety of translocations are
recognized which fall among the following three categories.
(i)Simple translocation:-These involve a single break in the chromosomes and the
transfer of broken piece of this chromosome to the end of another.since the terms of
unbroken chromosomes are nonsticky,such terminals chromosome attachment are
rarely,if ever found

8. (ii)Shift:- These involve three breaks and the transfer of a two break section of one
chromosome within the break produced in a nonhomologous chromosomes.Shift
are more common than simple translocations.

9. (iii)Reciprocal translocation or inter changes:- These are produced by single breaks
in two homologous chromosoe an exchange of chromosome section between
them,these are the most frequent and best studied translocation.

10. 2.Deletion
>Deletion is the loss of a chromosomal segment from any chromosome.Depending
upon the length of the lost chromosomal segment,the loss of genes involved may very
from sigle genes to block containing several gennes.
>The loss of chromosomal segment occurs when a portion of chromosome gets
detached due to certain reasons and the lost segment does not survive because it
lacks the centromere.
>The portion of the chromosome carrying the centromere fucntion as a genetically
defficient chromosome.

11. TYPES OF DELETIONS
1.Terminal deletions:- To the loss of segment from one or the other end of
chromosomes.The terminal acentric part of the chromosome is unable to survive and
causes terminal deletion.The terminal deletion is,caused by a single breks in a
chromosome.
2.Intercalary or Intestitial deletion: It denotes the loss of an intercalary segment of the
chromosomes with the reunion of terminal segments.The intercalary deletion is
characterised by two point breaks and the reunion of terminal parts.

12. 3.Duplication
>Sometimes a segment or a part of the chromosomes becomes repeated in the same
chromosomes.These additional duplicated segments are called duplications.
>They arise as a result of unequal crossing over between chromosomal segments.
>In Drosophila mutant bar eyes which are narrow and constricted are due to small
duplicated genes.
>It was observed that each additional duplicate segments made the eye smaller and
smaller.Sometimes duplications when act in opposite direction serve as supressors.

13. 4.Inversion
>Inversion is a kind of chromosomes aberration in which a chromosomal segment
exist in reverse relationship to the rest of its chromosomes.
>Inversions are beleived to arise by breakages at the point of intersection of a
chromosome loop and reunion with new partners.
>Any organism may be homozygous or heterozygous for an inversion.During
meiosis,inversion heterozygotes synapse by forming a looped configuration.
>In salivary gland chromosomes and other favourable material,an material,an inversion
loop makes it possible to determine with precision the extent of the aberration.

14. Types of Inversion
1.Paracentric inversion:- A single crossing over or an odd number of crossovers in the
inverted region will result into the formation of a dicentric chromosome(having two
centromeres) and an acentric chromosome(with no centromere).Of remaining two
chromatids one will be normal and the other will carry the inverison.
2.Pericentric inversion:- In a pericentric inversion(where centromere is present within
the inverted segment),although at pachytene,the configuration observed is similar to to
those describedabove for paracentric inversion,the products of crossing over the
configuraions at subsequent stages of meiosis differ,In the case,two of four
chromatids resulting after meiosis will have deficiencies and
duplications.However,unlike paracentric inversion,no dicentric bridge or acentric
fragment will be observed.

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