MEDEA = Maternal-Effect
Dominant Embryonic Arrest
 Medea
factors all share several characteristics:
- They breed true through the female line.
- They segregate in the male.
When a heterozygous Medea female (M/+) is crossed to a wild
type male (+/+), the M gene and its homolog segregate normally.
However, all progeny that do not inherit the Medea allele
die at or shortly after egg hatch. The lethality is maternal,
but the "rescue" is zygotic. The rescuing M allele
can be inherited from either parent.
There have been four well-studied Medea factors.
Of these, two (M-1 and M-4) are currently maintained at the
Tribolium Stock Center. Almost all M strains in the field
carry M-4. Of these, about a third also carry M-1. M-4 is
the only Medea factor present in North American and European
strains, being found in about half of them. Australian and
Indian strains are almost devoid of Medea factors. South American,
Asian, and African strains often have 2 or more M factors.
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