Define meta centric chromosome???
Answers
Answer:
Joan Vallès, ... Teresa Garnatje, in Advances in Botanical Research, 2011
B Karyotype Morphology
Artemisia karyotypes have most metacentric or submetacentric chromosomes, belonging to the m and sm categories according to Levan et al. (1964), and basically included in the 1A, 2A and 2B symmetry classes (Stebbins, 1971). This indicates that karyotypes are rather symmetrical. This is a common feature of the genus (Ehrendorfer, 1964; Korobkov, 1981; McArthur and Pope, 1979; McArthur and Sanderson, 1999; Persson, 1974; Vallès, 1987b; Vallès and Siljak-Yakovlev, 1997) and in tribe Anthemideae as a whole (Schweizer and Ehrendorfer, 1983). Chromosomes are not very long, ranging from 2 to 10 μm, with a mean length of around 4–6 μm. In dysploid x = 8 taxa, one or two clearly longer chromosome pairs confer to the karyotype a bigger degree of interchromosomal asymmetry, but, being almost perfectly metacentric, at the same time, they give a higher degree of intrachromosomal symmetry.
Following the widespread assumption that within angiosperms, asymmetrical karyotypes are derived from more symmetrical ones (Stace, 1989; Stebbins, 1971), it is perfectly plausible that in a genus such as Artemisia, belonging to a derived plant family, successive increases and decreases in karyotype symmetry could have occurred. The two major basic chromosome numbers (x = 9, x = 8) and the relationships between them are clear (see the above comments on descending dysploidy, which provided an increase in interchromosomal asymmetry), and given the high degree of karyotype symmetry dominating in the genus, it is to be assumed that most Artemisia karyotypes are secondarily symmetrical, following a mechanism considered usual by Stebbins (1971). The degree of karyotype symmetry in the genus is mostly useful at low taxonomic levels, basically concerning the relationships of closely related taxa, where a detailed karyotype analysis may indicate evolutionary trends. In this respect, asymmetrical karyotypes have been reported in representatives of the subgenera Dracunculus (Filatova, 1971) and Seriphidium (Filatova, 1974a,b), which appear as derived clades in molecular phylogenetic analyses (Garcia et al., 2011a; Pellicer et al., 2011). The karyotype of the tetraploid A. umbelliformis is more asymmetrical than that of diploid A. eriantha, suggesting a derived condition in the former, with the latter being at least one of the likely ancestors, and a similar situation is reported in the A. campestris complex (Oliva and Vallès, 1994; Vallès and Siljak-Yakovlev, 1997).
Explanation:
Normal chromosomes each have a single centromere. Its position along the chromosome can vary. Metacentric chromosomes have the centromere located midway between the ends of the chromosome, separating the two arms of the chromosome (Figure 1).
Explanation:
Metacentric chromosomes have the centromere located midway between the ends of the chromosome, separating the two arms of the chromosome (Figure 1). Chromosomes with centromeres positioned visibly off-center are called submetacentric.