3. Introduction
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Taxonomy
▰ It is a biological discipline producing the classification of the diversity found in the
biological domain.
▰ The classical taxonomy is dependent on morphological characters.
▰ These morphological characters have provided the foundation and framework for
taxonomy and are still indispensable to the systematists.
▻ However , taxonomists believe that morphological characters are not
sufficient for systematic classification of plants.
4. Taxonomic data sources
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Modern trends in taxonomy
▰ Taxonomists now accept that the morphological characters alone should not be
considered in systematic classification of plants.
▰ The complete knowledge of taxonomy is possible with the principles of various
disciplines such as cytology, genetics, anatomy, physiology etc.
▰ It has changed the face of classification from alpha to omega form
5. Taxonomic data sources
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Cytology (cyto-taxonomy)
▰ Study of cell is referred as cytology
▰ According to Solbrig et al.
▻ only the details of chromosomes have been used in resolving many taxonomic
problems
▰ The characteristics of the chromosome which have proved to be of taxonomic value
include:
1. Chromosome number 3. chromosome Morphology
2. Chromosome size 4. Chromosome behaviour at meiosis
6. Taxonomic data sources
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Cytology (cyto-taxonomy)
Chromosome number
▰ chromosome number, precise number of chromosomes typical for a given species.
▰ In sexually reproducing organisms, the number of chromosomes in the body (somatic) cells
typically is diploid (2n; a pair of each chromosome), twice the haploid (1n) number found in
the sex cells, or gametes.
Chromosome size
▰ The individual chromosomes of some taxa show marked differences in shape and size at
mitotic metaphase.
▰ The size of chromosome varies greatly in different families and also amongst members of
the same family. The monocotyledons usually have larger chromosomes than the
dicotyledons.
7. Taxonomic data sources-Contd..
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Cytology (cyto-taxonomy)
chromosome Morphology
▰ Usually the chromosomes are charaterized as median, sub-median, sub-terminal or terminal
with reference to their length and the position of centromere.
▰ Relative length of the arms of the chromosomes, position of centromere are some
characters of taxonomic significance
Chromosome behaviour at meiosis
▰ Significant taxonomic information may be obtained by the study of the behaviour of the
chromosomes during meiosis.
▰ Abnormalities in meiosis such as non-pairing, crossing-over, un-equal interchange etc. have
all proved to be systematic value
8. Taxonomic data sources-Contd..
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Molecular taxonomy
▰ Molecular taxonomy is the branch of science that deals with the presence of chemicals
inside our body.
▰ It is the method of identifying and distinguishing the specimens in a fast and exact manner
which is based on the interspecific variations.
▰ Molecular taxonomy helps in establishing the relationship of different plant groups at DNA
level.
▰ It unlocks the treasure chest of information on evolutionary history of organisms
▰ Over the past two decades, the use of molecular methods especially DNA sequence data
has had a profound influence on taxonomy.
▰ Molecular data have significant differences from traditional morphological data.
9. Taxonomic data sources-Contd..
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Molecular methods used in taxonomy
▰ Allozymes
▰ DNA Hybridization
▰ Restriction fragment length polymorphism ( RFLP)
Allozymes
▰ Allozymes are enzymes with identical function but distinct electrophoretic migration
patterns that are encoded by different alleles of the same locus.
▰ Allozymes ( also called alloenzymes) differ structurally but not functionally from other
allozymes coded for by different alleles at the same locus (Bader et al, 2016).
▰ Allozymes have traditionally been used to assess genetic variation within a population or
species, but they can also be used as data in phylogenetic analyses of closely related
species, e.g., species within a monophyletic genus (Annalisa Berta et al, 2015)
10. Taxonomic data sources-Contd..
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Molecular methods used in taxonomy
▰ Allozymes
▰ DNA Hybridization
▰ Restriction fragment length polymorphism ( RFLP)
DNA-DNA Hybridization
▰ DNA–DNA hybridization is a molecular biology technique that measures the degree of
genetic similarity between pools of DNA sequences.
▰ It is usually used to determine the genetic distance between two organisms and has been
used extensively in phylogeny and taxonomy.
11. Taxonomic data sources-Contd..
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Molecular methods used in taxonomy
▰ Allozymes
▰ DNA Hybridization
▰ Restriction fragment length polymorphism ( RFLP)
DNA-DNA Hybridization methods
▰ DNA–DNA hybridization methods used to identify genomic species have included
▻ nitrocellulose filter method
▻ the S1 endonuclease method
▻ the hydroxyapatite method
▻ and a quantitative bacterial dot filter method.
12. Taxonomic data sources-Contd..
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Molecular methods used in taxonomy
▰ Allozymes
▰ DNA Hybridization
▰ Restriction fragment length polymorphism ( RFLP)
Restriction fragment length polymorphism (RFLP)
▰ RFLP was developed by Botstein et al. (1980)
▰ In molecular biology, restriction fragment length polymorphism
(RFLP) is a technique that exploits variations in homologous
DNA sequences, known as polymorphisms, in order to
distinguish individuals, populations, or species or to pinpoint
the locations of genes within a sequence.
Working Principle
Notas do Editor
All these methods are time-consuming and laborious and can be applied only in special situations..
All these methods are time-consuming and laborious and can be applied only in special situations..
