Cytotaxonomy plant taxonomy

Cytotaxonomy
Prepared By-
Dr. Sangeeta Das
Assistant Professor
Department of Botany
Bahona College, Jorhat, Assam, India.

Cytotaxonomy
Cytology in Relation to Taxonomy:
It is the application of cytological data in solving
taxonomic problems.

Chromosome number:
The chromosome number is constant and same in
all individuals of a species.
It is used as a confirmative property to distinguish
a species from members of other specie

Example 1:
Separation at species level:
Monotropa hypopitys and Monotropa
hypophegea are two different species looks
like morphologically.
But they are separated on the basis of
chromosome numbers.
M. hypopitys is a hexaploid: 2n = 48
M. hypophegea is a diploid: 2n = 16

Example 2:
Separation at Interspecific level:
There are two cytotypes of the species
Veronica prostrata
On the basis of chromosome number, these
two cytotypes are raised to subspecies level
and named as
V. prostrata prostrata (n=8) and V. prostrata
scheerei (n=16).

Example 3:
Separation at Generic level:
Cicendia filiformis and Microcala pusilla are
placed in genus Cicendia
Separated based on chromosome number C.
filiformis (n =13); M. pusilla (n=10).
All species of the genus Tephrosia in
Fabaceae have 2n = 22, except T. constricta
having 2n = 16.
Therefore, the later is raised to a level of the
genus Sphinctospermum.

Example 4:
In the tribe Boranieae of Rutaceae,
the chromosomal base number
varies from 7 to 19.
Therefore, the members are
rearranged to have a unique system
of classification.

It is usually seen that closely related
plants, like the different species of a
genus, show chromosome numbers
which reveal an arithmetic relation with
one another
For example,
The different species of Piper show chromosome
numbers in multiples of 26, like 2n = 52 in P.
nigrum, 2n = 78 in P. betle, and 2n = 104 in wild
species of Piper (Mathew, 1958).

Separation at Family level:
Families are rearranged on the basis of
number and size of chromosomes.
For example,
Heleboreae and Anemoneae of
Ranunculaceae – chromosome number 7, 8
and 9
Both have large and small chromosome
Therefore, both the genera are rearranged.

Aneuploids:
Aneuploids are plants with basic number of
chromosome with some addition and
deletion of few chromosomes.
Monosomics have 2n – 1,eg., Datura.
Nullisomics have 2n -2, eg., Triticum
Trisomics have 2n + 2.
Tetrasomics have 2n + 2 chromosome.

Chromosome Size:
It has already been discovered that
evolutionary development involves in
addition to alterations in chromosome
number.
For example,
Cytologically Cyclea and Cissampelos are
seen to be based on 12, while Stephania
shows n = 13. It is seen that the number n =
13 is characteristic of the tribe Cocculeae,
which further shows chromosomes of small
size.

Large chromosomes, low
chromosome number and
symmetrical karyotype represent a
primitive status.
While small chromosomes, high
number and extreme asymmetry
indicate advancement.

Chromosome morphology:
Karyotype of plants is now very useful for the
classification of some plants.
Monocotyledons have larger chromosome number
than dicot.
Woody plants have smaller chromosome number than
herbs.

The position of centromere and satellite is considered
for classification.
For example,

 The shape of metaphase chromosome is
considered for classification.

Chromosomal behaviour:
It provides clues about the cause of sterility and
fertility among populations.
Structural difference in the parental chromosome
is the main cause for the sterility.
If the two sets of parental chromosomes are
homologous, the plants seem to be fertile.

Cytotaxonomy plant taxonomy