what is the definition of "homogeneous chromosomes" and ''heterologous chromosomes''
Answers
Soybean (Glycine max [L.] Merr.) is a major crop species and, therefore, a major target of genomic and genetic research. However, in contrast to other plant species, relatively few chromosomal aberrations have been identified and characterized in soybean. This is due in part to the difficulty of cytogenetic analysis of its small, morphologically homogeneous chromosomes. The recent development of a fluorescence in situ hybridization –based karyotyping system for soybean has enabled our characterization of most of the chromosomal translocation lines identified to date. Utilizing genetic data from existing translocation studies in soybean, we identified the chromosomes and approximate breakpoints involved in five translocation lines.
Keywords: soybean, chromosome translocation, FISH, karyotype, cytogenetics
Domesticated soybean (Glycine max [L.] Merr.) is a major crop species and the target of substantial investment of resources toward development of genetic and molecular maps, including the recently completed soybean genome sequencing project (Schmutz et al. 2010). However, the study of both classical and molecular cytogenetics of soybean has been relatively difficult and thus slower to develop. Very few large-scale structural aberrations have been characterized in soybean chromosomes (reviewed by Chung and Singh 2008): a few chromosomal inversion lines have been identified (reviewed by Palmer et al. 2000), and only seven accessions are known to involve the exchange of fragments between nonhomologous chromosomes (Palmer and Kilen 1987; Sellner, 1990; Mahama et al. 1999). The difficulty in characterizing even large-scale chromosomal aberrations in soybean can be attributed to their relatively large number (2n = 40; Veatch 1934), small size (∼2 µm), and morphological homogeneity (Ahmad et al. 1984; Singh and Hymowitz 1988). The inability to directly distinguish between different soybean chromosomes has meant that aberrations had to be characterized primarily by genetics, in combination with cytogenetics, to detect alterations in patterns of meiotic chromosome pairing. The best characterized reciprocal translocation line in soybean is Glycine soja P.I. 101404B, originally identified by Williams (Williams 1948) and genetically characterized by Palmer and Heer (1984). One breakpoint was positioned with respect to genetic markers on one of the two chromosomes involved (Sadanaga and Grindeland 1984; Mahama and Palmer 2003), chromosome 13 (Cregan et al. 1999; Cregan et al. 2001). This translocation appears to predominate in Chinese G. soja accessions (Palmer et al. 1987) and is indistinguishable from the exchange characterized in G. soja P.I. 464890B (Findley et al. 2010, discussed below).
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Answer:
A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization.
Genetic heterogeneity can be defined as mutations at two or more genetic loci that produce the same or similar phenotypes (either biochemical or clinical). This is relevant since genetic heterogeneity can present problems for heterozygote detection.
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