Symbols to Know for Crosses

• a/a – a is the allele and / represents the two chromatids – there are two alleles for a diploid organism

• a b/a b – two different genes on the same chromosome

• a/a ; b/b – two different genes on different chromosomes ; designated separate chromosomes

• X – symbolizes mating between two different individuals

• X - symbolizes a self cross – when the hermaphrodite worms fertilize their own eggs

• + is the wild type or non-mutant form of a gene

Creating a heterozygous male

Hermaphrodite Parent genotype

Male Parent genotype X

Male gametesFemale gametes

Progeny genotype

Which progeny are you continuing with? Why?

Progeny phenotypesand ratios

+/+ dpy/dpy

Hermaphrodite Parent genotype

Male Parent genotype X

Male gametesFemale gametes

F1 Progeny genotype and ratios

F1 Progeny phenotypes

Linkage 1: Cross with Unlinked unc

+/+ ; unc/unc

Linkage 2: Selfing of hermaphrodite from unlinked cross

hermaphrodite

X self cross

gametes

Progeny genotype

Progeny phenotypes and ratios

Hermaphrodite Parent genotype

Male Parent genotype X

Male gametesFemale gametes

Progeny genotype

Progeny phenotypesand ratios

Linkage 1: Crossing with Linked unc

Which progeny are you continuing with? Why?

+ unc/ + unc

Linkage 2: Selfing of hermaphrodite from linked cross

hermaphrodite

X self cross

gametes

Progeny genotype

Progeny phenotypes and ratios