Worm Breeder's Gazette 7(1): 82
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The pleiotropic suppressors sup 5 III and sup 7 X (Waterston,1981) have been used by several worm breeders as a means of identifying null alleles ( = amorphs ), because they appear to act only on a subset of null alleles, and not on missense alleles. Also, the extent and efficiency of suppression ( i.e., whether suppression is dominant or recessive) have been used as an indication of whether a particular gene product is needed in catalytic or stoichiometric amounts. While these indications are probably fairly reliable in general, it is possible to find exceptions. I have identified eight sup-7 suppressible alleles of tra-1 III : one (e1781) was derived from a general screen for tra mutants and seven were obtained by reversion of the dominant feminizing allele e1575 ( 'her-2'). Six of these have similar properties: they appear to be null alleles causing XX animals to develop into phenotypic XX males instead of hermaphrodites ) and suppression is recessive. The other two alleles are anomalous. One, e1825, is a weaker allele (i.e., not a complete null) because e1825 XX animals often have abnormal male tails, and they are never fertile males, nor are e1825/e1781 XX heterozygotes. The other anomalous allele, e1835, appears to be a null allele but it is unusual in that suppression is dominant rather than recessive. Since six out of eight alleles exhibit a consistent pattern, it is reasonable to regard the other two as exceptional. Precedents for such exceptions can be found among microbial amber mutations. However, the existence of the exceptions shows that, as usual, genetic data can sometimes be misleading.