Worm Breeder's Gazette 9(2): 100

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Analysis of the age-1 Locus by Three-Factor Crosses

P. Fitzpatrick and T. Johnson

Figure 1

MK546 has the genotype age-1(hx546) 6) II unc-31(
e169) IV; age-1 is a mutation conferring extended life and a 70% 
reduction in brood size.  It is tightly linked to fer-15.  By this 
criterion the age-1 locus has been mapped to linkage group II.  MK546 
is male sterile, but reisolates from crosses to N2 are male fertile, 
albeit at a reduced level.  An age-1 reisolate, TJ401, carries fer-15 
and is Brd (has about 30% of the progeny of N2) as was true for all 
other long-lived reisolates of age-1.  We have performed a series of 
three-factor crosses both to precisely localize the position of age-1 
and to separate by recombination the Brd and Age phenotypes, if 
possible.
A three-factor cross using dpy-10(e128) 44) II 
was performed by crossing TJ401 males with the double mutant and 
cloning Unc non-Dpy and Dpy non-Unc F3 progeny; subsequently, assays 
for Brd, Age, and Fer were performed on their progeny.  Among the 
recombinants were 8 Fer  10 non-Fer Dpy non-
Unc, and 1 recombinant non-Fer Unc non-Dpy.
The recombinants were scored for Brd by assaying the number of 
progeny produced by 3 individuals.  Parents were allowed to lay on 
individual plates and were transferred every 2 days until sterile.  
The progeny were counted 1 day after the removal of the parents.  All 
Fer recombinants were Brd, and all non-Fer recombinants were non-Brd.  
This places the fer-15 and brd loci 0.5 to 1.5 map units to the right 
of dpy-10.  Scoring of Age proved difficult because unc-52 
significantly reduces life-span.
A second three-factor cross using dpy-10(e128) 0) 
II allows more precise mapping.  58 recombinants were analyzed: 25 
were Dpy non-Unc and 33 Unc non-Dpy.  Brd was scored as before and 
again showed complete linkage between fer-15 and brd.  The following 
data position brd and fer-15 0.6 map units to the right of dpy-10.[See 
Figure 1]
The dpy-10 and unc-4 loci affect life-span.  Since age-1 is 
recessive with regard to life-span, we have been trying to score life-
span on dpy-10 or unc-4 F1 heterozygote males obtained by backcrossing 
recombinants to TJ401.  Controls consisted of N2 males, F1 males of 
unc-4 by TJ401 males, F1 males of dpy-10 by TJ401 males, and TJ401 
males.  Our data currently suggests that the age-1 gene may be 
separable from the brd and fer-15 genes by as much as 0.5 map units, 
but we remain uncertain of the interpretations of the age-1 genotype 
derived from the analysis of heterozygotes.
A third three-factor cross is underway using a triple heterozygote (
dpy-10 unc-4) male, test-crossed to dpy-10 
odites.  Wild-type recombinants in the male 
can be identified and subsequently scored for Age and Brd without the 
interference of the dpy-10 and unc-4 mutant loci which make difficult 
the reliable scoring of the life-span phenotype of the age-1 locus.

Figure 1