Marker assisted breeding involves using genetic markers associated with traits of interest to assist plant breeders in selecting desirable plants. There are two main types of genetic markers - allozymes and isozymes. Allozymes are multiple alleles of the same gene that code for similar but structurally different enzymes, while isozymes are encoded by different genes and may differ more substantially in sequence and structure. Both can be detected using electrophoresis techniques that separate proteins by charge and size. Genetic markers provide a quicker way to select plants with desired traits compared to phenotypic selection alone.
4. Some important
terms and
concepts of
marker
Allozymes and Isozymes
protein molecules are coded by genes.
Some enzymes are coded by different alleles of the same gene
present at the same locus,They are known as allozymes.
some enzymes are coded by different genes located at different
loci. These enzymes are known as isozymes.
Therefore, multiple alleles at one locus code for allozymes.
They show a small difference in their amino acid sequences or
structure. However, they carry out a very similar function.
The small differences existing among allozymes is due to
the mutations, or random changes occurred in DNA sequences.
5. These tiny differences
can be detected by
capillary electrophoresis
based on the molecular
sizes and electrical
charges.
If the organisms are
closely related, there
would be fewer changes
between allozymes.
isozymes are multiple
forms of an enzyme
coded by different
genes.
Structurally, isozymes
slightly differ from their
amino acid sequences.
Hence, they consist of
different shapes and
sizes. But they catalyze
the same biochemical
reaction
6. What is the Difference
Between Allozymes and
Isozymes?
• A single gene produces multiple forms of an
enzyme
called allozymes
• Different genes produce multiple forms of an
enzyme called isozymes.
7. Allozyme and isozyme as
marker
• Isoenzyme and alloenzyme differ in their physical and chemical
property such as,protein structure , amino acid
sequence, electrophoretic mobility.
• Marker are based on capillary electrophoresis techniques
• C.E.T are performed in a liquid rather than generally gel , they are
based on molecular mass.
• When a mutation in the DNA results in an amino acid being replaced, the
net electric charge of the protein may be modified, and the overall shape
(conformation) of the molecule change.
• Because of changes in electric charge and conformation can affect the
migration rate of proteins in an electric field
• allelic variation can be detected by gel electrophoresis and subsequent
enzyme-specific stains that contain substrate for the enzyme,
8. Advantage Disadvantage
Doesn’t require DNA extraction or the
availability of sequence information, primers
or probes
relatively low abundance and low level of
polymorphism.
Simple analytical procedures, allow some
allozymes to be applied at relatively low
costs,
. Like phenotypic markers they may be
affected by environmental conditions
Allozymes are codominant markers that have
high reproducibility
Stage and tissue specific.
they are quick and easy to use.
9. Dna polymorphism
• Polymorphism, as related to
genomics, refers to the
presence of two or more
variant forms of a specific
DNA sequence that can
occur among different
individuals or populations.
The most common type of
polymorphism involves
variation at a single
nucleotide (also called a
single-nucleotide
polymorphism, or SNP).
10. D.N.A MARKER & IT`S TYPE
Hybridisation
based
• R.F.L.P(restriction
fragment length
polymorphism)
P.C.R based
D.N.A Marker
• R.A.P.D (restriction
amplified polymorphic
D.N.A)
• A.F.L.P(Amplified
Fragment length
polymorphism )
Sequence
based D.N.A.
Marker
• S.N.P(single Nucleotide
Polymorphism)
• S.S.R(simple sequence
repeat)
• I.S.S.R(inter simple
sequence repeat)
Types of D.N.A
Markers:-
