Cytology is defined as the scientific study of cells, particularly their microscopic characteristics and functions. It is often used in medical diagnostics to identify diseases, especially cancer
Cytology, the study of cells, plays a crucial role in plant taxonomy, particularly through the emerging field of cytotaxonomy, which utilizes cytological data to resolve taxonomic issues. Here are the key taxonomic evidences derived from cytology:
1. Chromosome Number
The chromosome number is a fundamental taxonomic character, often remaining constant within a species but varying significantly between species. This constancy can be used to distinguish species, as seen in:
Polyploidy: Polyploid species are recognized as distinct only if they exhibit morphological differences. For example, in the genus Saxifraga, Saxifraga hyperborean (2n = 26) and Saxifraga rivularis (2n = 52) are identified as separate species due to their differing chromosome counts.
Aneuploidy: Changes in chromosome number can occur due to aneuploidy (addition or deletion of chromosomes) or polyploidy (addition of complete sets of chromosomes), which can also inform taxonomic classifications. For instance, Tephrosia constricta (2n = 16) was separated into a new genus based on its unique chromosome number compared to other species in the Tephrosia genus, which have 2n = 22.
2. Chromosome Morphology
Chromosome morphology, including karyotype structure, is critical for taxonomic classification. Key aspects include:
Karyotype Analysis: The karyotype is a representation of the chromosome set of a species. Symmetrical karyotypes (similar chromosomes) are considered primitive, while asymmetrical karyotypes (varied chromosome types) are viewed as advanced. For example, the family Agavaceae displays a bimodal karyotype that supports its classification based on chromosomal similarities.
Chromosome Size and Structure: Changes in chromosome size and structure, such as the presence of secondary constrictions or satellites, can provide insights into evolutionary relationships and aid in the classification of families like Ranunculaceae.
3. Chromosomal Behavior
The behavior of chromosomes during meiosis is significant for understanding phylogenetic relationships:
Meiotic Behavior: Observations of chromosomal pairing and separation during meiosis can reveal relationships among species. For example, the hexaploid Senecio cambrensis has been identified as an allohexaploid resulting from hybridization between Senecio vulgaris and Senecio squalidus.
Genome Analysis: Cytological studies have confirmed relationships among species through genomic analysis, such as the derivation of hexaploid bread wheat (Triticum aestivum) from its diploid and tetraploid ancestors.
Cytological evidence, including chromosome number, morphology, and behavior, provides essential insights for plant taxonomy, helping to resolve taxonomic ambiguities and clarify evolutionary relationships among plant species.