Deficiency of recombinant genotypes in a trans test cross
With respect to the arrangement of linked
loci in dihybrid individuals (AaBb), a trans arrangement
refers to the presence of the alternate dominant and
recessive alleles at either locus on either chromosome, (Ab/)
and (aB/). The genotype of the dihybrid
individual is written as (Ab//aB). Because crossover
between loci is more or less uncommon, the offspring of a
cross between a trans dihybrid
and an ab//ab
tester will produce a larger fraction of the parental
phases (Ab//ab
and aB//ab)
than of the recombinant types (AB//ab and ab//ab). Note that the
recombinant types are in cis,
with the dominant alleles at both loci on the same
chromatid.