Locus M (Merle)

Locus M (Merle)

The M locus affects the merle pattern by creating areas of diluted and fully pigmented coat.
Merle is caused by a SINE insertion in the PMEL gene.
The length of the polyA tail determines how strong the merle expression will be.

Alleles at the M locus

• m — Non-merle

• No merle pattern

• Safe in all combinations

• Mc / Mc+ — Cryptic merle

• Very short polyA tail

• Often looks like a normal dog

• Can unexpectedly produce merle puppies

• Ma / Ma+ — Atypical merle

• Mild or minimal merle expression

• Subtle diluted shading; sometimes almost invisible

• M — Classic merle

• Typical merle pattern with diluted patches

• Blue or partially blue eyes can occur

• Mh — Harlequin merle

• Strongest merle variant

• Very pale/white large patches

• Merle Mosaic — (multiple merle alleles in one dog)

• Dog carries more than two merle allele lengths due to early embryonic mutation

• Coat pattern can be irregular or atypical

• Different tissues (cheek swab vs. semen) may show different results

• Needs careful pairing due to hidden risky alleles

Inheritance and safety

• Merle is dominant.

• One allele is enough to show merle.

• Two merle alleles → high risk.

✓ Safe combinations

• m/m

• m/Mc

• m/Mc+

• m/Ma

• m/Ma+

• m/M

⚠️ High-risk combinations

May cause hearing or vision problems:

• M/M

• Mh/M

• Mh/Mh

• Ma+/M

• Ma+/Mh

• Mc+/Mh

• Mc/Mh

Why this test is important

• Detects cryptic merle carriers

• Prevents accidental double-merle litters

• Helps breeders plan safe, healthy pairings

• Determines whether a dog carries mild, classic, or harlequin merle variants

Test Results Preview