Cytotaxonomy

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Cell in anaphase the chromosomes having split and the kinetochore microtubules shrinking Anaphase IF.jpg
Cell in anaphase the chromosomes having split and the kinetochore microtubules shrinking

Cytotaxonomy is the classification of organisms using comparative studies of chromosomes during mitosis.

Description

Cytotaxonomy is a branch of taxonomy that uses the characteristics of cellular structures to classify organisms. In cytotaxonomy, the chromosomal configuration of an organism is the most widely used parameter to infer the relationship between two organisms. The inference of species relationships is based on the assumption that closely related species share similar characteristics in their chromosomal setup (referred to as karyotype). [1] [2] By analysing the similarities and differences in the chromosomes, karyotype evolution and species evolution can be reconstructed.

The number, structure, and behaviour of chromosomes is of great value in taxonomy, with chromosome number being the most widely used and quoted character. Chromosome numbers are usually determined at the metaphase stage during mitosis. Usually, the diploid chromosome number (2n) is referenced, unless dealing with a polyploid series in which case the base number or number of chromosomes in the genome of the original haploid is quoted. Another useful taxonomic character is the position of the centromere. Meiotic behaviour may show the heterozygosity of inversions. This may be constant for a taxon, offering further taxonomic evidence.

Often, cytological evidence is accompanied and strengthened by other analyses, including genomics and DNA-based phylogenies.

Cytology has contributed to tracking the evolutionary history of many organisms, especially primates and flowering plants. As example, karyotype comparisons have largely clarified the evolution of Arabidopsis thaliana [3] and of saffron crocus, [4] though there are many more studies that deserve highlighting.

Related Research Articles

<span class="mw-page-title-main">Chromosome</span> DNA molecule containing genetic material of a cell

A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by chaperone proteins, bind to and condense the DNA molecule to maintain its integrity. These chromosomes display a complex three-dimensional structure, which plays a significant role in transcriptional regulation.

<span class="mw-page-title-main">Centromere</span> Specialized DNA sequence of a chromosome that links a pair of sister chromatids

The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers attach to the centromere via the kinetochore.

<span class="mw-page-title-main">Genome</span> All genetic material of an organism

In the fields of molecular biology and genetics, a genome is all genetic information of an organism. It consists of nucleotide sequences of DNA. The nuclear genome includes protein-coding genes and non-coding genes, the other functional regions of the genome, and any junk DNA if it is present. Algae and plants contain chloroplasts with a chloroplast genome and almost all eukaryotes have mitochondria and a mitochondrial genome.

<span class="mw-page-title-main">Ploidy</span> Number of sets of chromosomes in a cell

Ploidy is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively, in each homologous chromosome pair, which chromosomes naturally exist as. Somatic cells, tissues, and individual organisms can be described according to the number of sets of chromosomes present : monoploid, diploid, triploid, tetraploid, pentaploid, hexaploid, heptaploid or septaploid, etc. The generic term polyploid is often used to describe cells with three or more chromosome sets.

<i>Arabidopsis</i> Genus of flowering plants

Arabidopsis (rockcress) is a genus in the family Brassicaceae. They are small flowering plants related to cabbage and mustard. This genus is of great interest since it contains thale cress, one of the model organisms used for studying plant biology and the first plant to have its entire genome sequenced. Changes in thale cress are easily observed, making it a very useful model.

<i>Arabidopsis thaliana</i> Model plant species in the family Brassicaceae

Arabidopsis thaliana, the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. A. thaliana is considered a weed; it is found along the shoulders of roads and in disturbed land.

<span class="mw-page-title-main">Polyploidy</span> Condition where cells of an organism have more than two paired sets of chromosomes

Polyploidy is a condition in which the cells of an organism have more than one pair of (homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains one or more chromosomes and comes from each of two parents, resulting in pairs of homologous chromosomes between sets. However, some organisms are polyploid. Polyploidy is especially common in plants. Most eukaryotes have diploid somatic cells, but produce haploid gametes by meiosis. A monoploid has only one set of chromosomes, and the term is usually only applied to cells or organisms that are normally diploid. Males of bees and other Hymenoptera, for example, are monoploid. Unlike animals, plants and multicellular algae have life cycles with two alternating multicellular generations. The gametophyte generation is haploid, and produces gametes by mitosis, the sporophyte generation is diploid and produces spores by meiosis.

<span class="mw-page-title-main">Karyotype</span> Photographic display of total chromosome complement in a cell

A karyotype is a preparation of the complete set of metaphase chromosomes in the cells of a species or in an individual organism, sorted by length, centromere location and other features and for a test that detects this complement or counts the number of chromosomes. Karyotyping is the process by which a karyotype is prepared from photographs of chromosomes, in order to determine the chromosome complement of an individual, including the number of chromosomes and any abnormalities.

<span class="mw-page-title-main">Cytogenetics</span> Branch of genetics

Cytogenetics is essentially a branch of genetics, but is also a part of cell biology/cytology, that is concerned with how the chromosomes relate to cell behaviour, particularly to their behaviour during mitosis and meiosis. Techniques used include karyotyping, analysis of G-banded chromosomes, other cytogenetic banding techniques, as well as molecular cytogenetics such as fluorescent in situ hybridization (FISH) and comparative genomic hybridization (CGH).

<span class="mw-page-title-main">GC-content</span> The percentage of guanine and cytosine in DNA or RNA molecules

In molecular biology and genetics, GC-content is the percentage of nitrogenous bases in a DNA or RNA molecule that are either guanine (G) or cytosine (C). This measure indicates the proportion of G and C bases out of an implied four total bases, also including adenine and thymine in DNA and adenine and uracil in RNA.

<span class="mw-page-title-main">Paleopolyploidy</span> State of having undergone whole genome duplication in deep evolutionary time

Paleopolyploidy is the result of genome duplications which occurred at least several million years ago (MYA). Such an event could either double the genome of a single species (autopolyploidy) or combine those of two species (allopolyploidy). Because of functional redundancy, genes are rapidly silenced or lost from the duplicated genomes. Most paleopolyploids, through evolutionary time, have lost their polyploid status through a process called diploidization, and are currently considered diploids e.g. baker's yeast, Arabidopsis thaliana, and perhaps humans.

<i>Crocus sativus</i> Species of plant, saffron crocus

Crocus sativus, commonly known as saffron crocus, or autumn crocus, is a species of flowering plant of the Crocus genus in the iris family Iridaceae. It is best known for producing the spice saffron from the filaments that grow inside the flower. The term "autumn crocus" is also used for species in the Colchicum genus, which strongly resemble crocuses. However, crocuses have three stamens and three styles, while colchicums have six stamens and one style, and belong to a different family, Colchicaceae. Colchicums are also toxic.

<i>Crocus cartwrightianus</i> Species of flowering plant

Crocus cartwrightianus is a species of flowering plant in the family Iridaceae, native to mainland Greece and Crete. It is a cormous perennial growing to 5 cm (2 in). The flowers, in shades of lilac or white with purple veins and prominent red stigmas, appear with the leaves in autumn and winter.

Evolutionary developmental biology (evo-devo) is the study of developmental programs and patterns from an evolutionary perspective. It seeks to understand the various influences shaping the form and nature of life on the planet. Evo-devo arose as a separate branch of science rather recently. An early sign of this occurred in 1999.

<span class="mw-page-title-main">LTR retrotransposon</span> Class I transposable element

LTR retrotransposons are class I transposable element characterized by the presence of long terminal repeats (LTRs) directly flanking an internal coding region. As retrotransposons, they mobilize through reverse transcription of their mRNA and integration of the newly created cDNA into another location. Their mechanism of retrotransposition is shared with retroviruses, with the difference that most LTR-retrotransposons do not form infectious particles that leave the cells and therefore only replicate inside their genome of origin. Those that do (occasionally) form virus-like particles are classified under Ortervirales.

<span class="mw-page-title-main">Plant genetics</span> Study of genes and heredity in plants

Plant genetics is the study of genes, genetic variation, and heredity specifically in plants. It is generally considered a field of biology and botany, but intersects frequently with many other life sciences and is strongly linked with the study of information systems. Plant genetics is similar in many ways to animal genetics but differs in a few key areas.

Arabidopsis thaliana is a first class model organism and the single most important species for fundamental research in plant molecular genetics.

Holocentric chromosomes are chromosomes that possess multiple kinetochores along their length rather than the single centromere typical of other chromosomes. They were first described in cytogenetic experiments in 1935. Since this first observation, the term holocentric chromosome has referred to chromosomes that: i) lack the primary constriction corresponding to the centromere observed in monocentric chromosomes; and ii) possess multiple kinetochores dispersed along the entire chromosomal axis, such that microtubules bind to the chromosome along its entire length and move broadside to the pole from the metaphase plate. Holocentric chromosomes are also termed holokinetic, because, during cell division, the sister chromatids move apart in parallel and do not form the classical V-shaped figures typical of monocentric chromosomes.

<span class="mw-page-title-main">Sexual selection in Arabidopsis thaliana</span>

Sexual selection in Arabidopsis thaliana is a mode of natural selection by which the flowering plant Arabidopsis thaliana selects mates to maximize reproductive success.

References

  1. Guerra, M. (2012-09-01). "Cytotaxonomy: The end of childhood". Plant Biosystems. 146 (3): 703–710. doi:10.1080/11263504.2012.717973. ISSN   1126-3504. S2CID   81999232.
  2. Guerra, M. (2008). "Chromosome numbers in plant cytotaxonomy: concepts and implications". Cytogenetic and Genome Research. 120 (3–4): 339–350. doi:10.1159/000121083. ISSN   1424-8581. PMID   18504363. S2CID   41944235.
  3. Lysak, Martin A.; Berr, Alexandre; Pecinka, Ales; Schmidt, Renate; McBreen, Kim; Schubert, Ingo (2006-03-28). "Mechanisms of chromosome number reduction in Arabidopsis thaliana and related Brassicaceae species". Proceedings of the National Academy of Sciences. 103 (13): 5224–5229. doi: 10.1073/pnas.0510791103 . ISSN   0027-8424. PMC   1458822 . PMID   16549785.
  4. Schmidt, Thomas; Heitkam, Tony; Liedtke, Susan; Schubert, Veit; Menzel, Gerhard (2019). "Adding color to a century-old enigma: multi-color chromosome identification unravels the autotriploid nature of saffron (Crocus sativus) as a hybrid of wild Crocus cartwrightianus cytotypes". New Phytologist. 222 (4): 1965–1980. doi:10.1111/nph.15715. ISSN   1469-8137. PMID   30690735. S2CID   59338870.