Cytotaxonomy

Cytotaxonomy deals with classification of plants using cytological characters. This PPT will help the students for better understanding of the topic

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.

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