Worm Breeder's Gazette 17(1): 38 (October 1, 2001)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Identifying male fertility genes by recombinant inbred mapping

Marc Hammarlund, Erik M. Jorgensen

Department of Biology, University of Utah, Salt Lake City UT 84112-0840

We have found that the Hawaiian race CB4856 exhibits much higher male fertility than N2 Bristol.  We initially observed that a CB4856 mating plate can be maintained indefinitely by repeated chunking, while an N2 mating plate becomes dominated by hermaphrodites after a few generations. Since CB4856 hermaphrodites are not Him (1), the sustained presence of males must be due to more efficient mating.


Increased mating efficiency is a property of CB4856 males rather than hermaphrodites. We tested the four possible matings between males and hermaphrodites of both races.  Single L4 males were mated to three adult hermaphrodites and transferred daily to new hermaphrodites, and successful matings were scored by the presence of males.  Strikingly, by the fourth day of mating N2 males were almost completely sterile (1/19 successful) while CB4856 males mated well (10/15 successful).  The race  of the hermaphrodite played no role in increased mating.  Moreover, when we tested heterozygous males, CB4856 male fertility was dominant to N2 infertility.


The npr-1 locus is a source of behavioral differences between N2 and CB4856 (2). Thus, we tested N2 males that carry the EMS-induced npr-1(n1353) allele.  npr-1(n1353)animals, like CB4856, border and clump on bacterial lawns.  However, npr-1(n1353) males did not have increased fertility compared to N2, suggesting that the npr-1 pathway does not control male fertility.


Hodgkin and Doniach (1) described extended male fertility in the Stanford race CB4855. The increase in fertility was dominant over N2, and loci on LGIV, LGX, and possibly LGV contributed to this behavior.  Our data suggest that at least some of the loci governing male fertility are similar in the Hawaiian and Stanford races.


To determine the molecular basis of this difference in male fertility we are cloning the relevant genes.  As a first step in cloning, we are using recombinant inbred mapping to locate the genes that determine male fertility differences between N2 and CB4856.  In recombinant inbred mapping a large number of self-progeny are cloned from a heterozygote between the two strains of interest.  Single self-progeny are cloned from each animal, and this is repeated for 10 generations.  Each line thus generated is homozygous for a random sample of parental alleles, approximately half of each.  The phenotype and genotype of each line is then determined. Recombinant inbred mapping is ideal for potentially complex phenotypes because it can identify multiple genes simultaneously, including modifiers.


We have generated a large number of inbred lines from N2/CB4856 heterozygotes and are currently characterizing them for male fertility and genotype.  Thanks to the very large number of SNP markers between N2 and CB4856 (3), we will be able to quickly construct maps for each strain.  In addition to male mating, these lines are useful for mapping any other phenotypic difference between the N2 and the Hawaiian race. 


1.  Hodgkin, J and Doniach, T, Genetics 146, 1997.

2.  de Bono, M and Bargmann, C, Cell 94, 1998.

3.  Wicks, S et al., Nature Genetics 28, 2001.