Heterozygotes deposit
yellow
pignment along the entire length of hair shafts.
The wild type
agouti phenotype is caused by
yellow pigment deposited
in a band
on a
black hair shaft.
The AY mutation is a deletion in the yellow gene and extending into an adjacent gene (Merc), which is critical to embryonic development.
The "loss of function" in a Merc mutant causes AY/AY
homozygotes to die before birth.
Heterozygotes deposit
yellow
pignment along the entire length of hair shafts.