Unequal crossover

Besides unequal crossover and transposition, a third mechanism can effect rapid changes in the genetic material. Similar sequences on homologous or nonhomol-ogous chromosomes may occasionally pair up and eliminate any mismatched sequences between them. This may lead to the accidental fixation of one variant or another throughout a family of repeated sequences and thereby homogenize the sequences of the members of repetitive DNA families. This latter process is referred to as gene conversion. 

Large segment deletion (unequal crossover in meiosis) Loss of fimrtion shorter than normal or entirely missing... 

Frameshift mutations may be produced by various mechanisms. For instance, intercalation of planar molecules, such as acridine within the DNA molecule, allows base insertions at replication. Acridine-type compounds may also induce mutations of the frameshift type by interfering with the excision and repair processes, which correct errors occurring during unequal crossover between homologous chromosomes at meiosis. Such unequal crossover gives rise to errors of the frameshift type. 

Nunoya K, Yokoi T, Takahashi Y, Kimura K, Kinoshita M, Kamataki T. Homologous unequal crossover within the human CYP2A gene cluster as a mechanism for the deletion of the entire CYP2A6 gene associated with the poor metabolizer phenotype. J Biochem (Tokyo) 1999 126(2) 402-407. 

Gene duplication clearly plays an important role in the evolution of LDH as it does in the evolution of dehydrogenases in general. It may be caused either by unequal crossover of chromosomes or by chromosomal duplication. 

Many mutations are known because of the relationship of the gene with congenital adrenal hyperplasia". These include a 5-base duplication and clusters of mutations in exons 6-8 (ref [1175]). The high similarity and proximity of the CYPllBl and CYPllBl genes appear to lead to mutant generated by unequal crossover and inactive chimeric product" " . Splice donor site mutations are also known" ". 

Pascoe, L., K.M. Curnow, L. Slutsker, J.M. Connell, P.W. Speiser, M.I. New etal. (1992). Glucocorticoid-suppressible hyperaldosteronism results from hybrid genes created by unequal crossovers between CYPllBl and CYP11B2, Proc. Natl. Acad. Sci. USA 89, 8327-8331. 

This apparent variation in the efficiency of concerted evolution within gene families and between families whose members presumably experience the same types of evolutionary constraints suggests that it is dangerous to assume that the question of orthoiogy can be ignored in families in which concerted evolution is thought to be the rule. In addition to this problem, the process of concerted evolution may itself result in a loss of cladistic information. The primary mechanisms of concerted evolution, such as unequal crossover and gene conversion, involve recombinational... 

Paseoe L, Curnow K, Slutsker L, Connel JMC, peiser PW, New MI, White PW (1992) Glucocor-ticoid-suppressible hyperaldosteronism results from hybrid genes created by unequal crossover between CYPl 1B1 and CYPl 1B2. Proc Natl Acad Sci U S A 89 8327-8331... 

---