Linkage, centromere

Several of the mannan mutants have been placed on the genetic map (Figure 8), and it is notable that the first two mapped were centromere-linked (23> O). Centromere linkage is postulated to favor retention of a gene by minimizing recombination. 

FIGURE 4, Duplication strains of A. nidulans. Linkage groups I and II are shown by unbroken and broken lines, respectively. Symbols O, centromere y, recessive mutant allele determining yellow conidia ad, bi, recessive mutant alleles determining requirements, respectively, for adenine and biotin. Deletion of dominant alleles produces sectors differing from the parent in conidial color or nutritional requirements. 

Fig. 16.9 The genetic map of S. cerevisiae [74]. Centromeres are represented as circles, the left arm of each chromosome being drawn above the centromere. Dashed and dotted lines represent linkages established other than by tetrad analysis. Parentheses enclose genes where exact orientation is unknown. (Published by kind permission of Dr R. K. Mortimer.)...

Class E. Mutants with long flagella. Two mutants with abnormally long flagella have been isolated. The first, If 1, is located on linkage group II between the centromere and one of the center tubule loci, pf 18. The second. If 2, is not linked to If 1 and has not yet been mapped. 

---