Homologous chromosomes

How can different distribution patterns within the same species be reconciled This seeming paradox is resolvable in a variety of ways, all of which are experimentally testable. For example, variants that are homogenized and restricted to specific chromosomes might be relatively young such that insufficient time has elapsed to allow for the transfer of the mutation in question to other relevant chromosomes (homologous or... 

Morescalchi M.A., Schempp W., Consigliere S., Bigoni F., Wienberg J., Stanyon R. (1997). Mapping chromosomal homology between humans and the black-handed spider monkey by fluorescence in situ hybridization. Chromosome Res. 5 527-536. 

Chromosomal homology between the human and the bovine DMRTl genes. Folia biologica (Krakow), Vol.57, No.1-2, pp. 29-32, ISSN 0015-5497... 

Fig. 3. Homologous chromosomes having evenly spaced genetic markers (1 9). The segregation of the or quantitative trait loci (QTL) can be followed using marker 2. Polymorphisms within marker 2 can be used to foUow the segregation of the genes within the QTL, even though the exact location or...

All phosphoinositides are found in the cytosolic half of the lipid bilayer of the plasma or intracellular compartment membranes (left part). The different kinases acting on phosphoinositides in mammalian cells are shown in solid lines and the phosphoinositide 3-kinases, in bold. The phosphoinositides counterpart pathways catalysed by known phosphatases are represented by dashed lines. The best known phosphatases are PTEN (Phosphatase and tensin homolog deleted on chromosome 10) and SHIP (SH2 domain-containing inositol 5-phosphatase). 

Phospholipid phosphatases are enzymes such as SHIP (SH2-domain containing inositide-5-phosphatase) or PTEN (phosphatase and tensin homolog deleted on chromosome 10) which dephosphorylate phosphoino-sitides. Whereas SHIP removes phosphate from the 5 ... 

Figure 36-9. The process of crossing-over between homologous metaphase chromosomes to generate recombinant chromosomes. See also Figure 36-12.

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. 

Gene knockouts were performed by homologous recombination in mice. The enzymes are characterized as neuronal, inducible (macrophage), and endothelial because these were the sites in which they were first identified. However, all three enzymes have been found in other sites, and the neuronal enzyme is also inducible. Each gene has been cloned, and its chromosomal location in humans has been determined. 

The discovery that MAO has two isoenzymes with different distributions, substrate specificity and inhibitor sensitivity has helped to rehabilitate the MAOIs to some extent. These isoenzymes are the products of different genes on the X-chromosome and share about 70% sequence homology. Whereas noradrenaline and 5-HT are metabolised preferentially by MAOa, tyramine and dopamine can be metabolised by either isoenzyme. Selective inhibitors of MAOa (e-g- moclobemide Da Prada et al. 1989) should therefore be safe and effective antidepressants whereas the selective MAOb inhibitor, selegiline, should not have any appreciable antidepressant activity (Table 20.5). 

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