This document discusses how cytology, the study of cells, is used in taxonomic studies of plants. Chromosome number, morphology, and behavior during meiosis provide clues about genetic relationships. Species are distinguished based on consistent chromosome numbers. Examples show how different species and genera of plants have been separated or reclassified based on differences in their chromosome numbers, sizes, shapes, and behavior during cell division. Aneuploid plants with extra or missing chromosomes are also discussed.

1. CYTOTAXONOMY

2. Taxonomy in relation to Cytology
• The cytological characters of
chromosome number, morphology and
chromosomal behavior during meiosis
are used in taxonomic studies
• They provide an idea of genetic
relationships between plant populations

3. Based on 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 species

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

5. Interspecific separation
Ex: 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
• V. prostrata prostrata : n = 8
• V. prostrata scheerei : n = 16

6. Separation at Generic level
Ex - 1
• Cicendia filiformis and Microcala pusilla –
placed in genus Cicendia
• Separated based on chromosome number
C. filiformis : n = 13; M. pusilla : n = 10
Ex – 2
• All species of the genus Tephrosia in
Fabaceae have 2n = 22, except T. constricta
having 2n = 16
• So the later is raised to a level of the genus
Sphinctospermum

7. Ex – 3
• In the tribe Boranieae of Rutaceae, the
chromosomal base number varies from
7 to 19.
• So the members are rearranged to have
a unique system

8. Separation at Family level
• Families are rearranged on the basis of number and
size of chromosomes
Ex 1:
• Heleboreae and Anemoneae of Ranunculaceae –
chromosome number 7, 8 and 9
• Both have large and small chromosome
• So the genera are rearranged
Ex 2
• Ranunculaceae – n = 7 and small chromosome
placed in Thalictreae
• n = 9 and large chromosome placed in Coptodeae

9. 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 Eg: Wheat
Tetrasomics have 2n + 2
chromosomes

10. Based on 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 shape of metaphase chromosome is
considered for classification
• The position of centromere and satellite
is considered for classification

11. Eg:
• Acrocentric – centromere at one end
• Acentric – No centromere
• Metacentric – centromere at the middle
• Telocentric – centromere near one end

12. Based on 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.

13. THANK YOU