Dark Locus: Marble Phenotypes
The allele for marble is on the dark locus
and is designated with the symbol M.
The
non-wild
alleles at this locus
at this
locus that appear in marble phenotypes are:
Marble (M), Gold Marble (Gm), Gold (g)
Marble (M) is
co-dominant with the wild type allele (+). It is recessive to the
dark allele (D) and is dominant to gold marble (Gm) and gold (g)
alleles.
Two distinct
phenotypes of marble occur: marble and silver marble. The table
below summarizes how the allele for marble interacts with other
alleles at this locus to form the marble phenotypes.
|
MARBLE PHENOTYPES |
|
Phenotype: |
Marble |
Silver Marble
(Barred Marble) |
|
Genotype: |
M/M, M/Gm, or
M/g |
M/+ |
|
Pattern of inheritance: |
Marble is
dominant to Gold Marble and Gold. |
Marble is
co-dominant with wild type (blending of traits) |
Marble
Marble may be homozygous, with two alleles for the marble trait (M/M),
or it may be heterozygous with one marble allele paired with either a
gold marble allele (M/Gm) or with a gold allele (M/g).
A homozygous marble is mostly black with a small amount of white
marbling. Some marbles will also exhibit orange on the crown. The
tail, dorsal and anal fins will typically exhibit some combination of
black and white bands or stripes running the length of the tail or
fin. Occasionally an entire fin or tail may be completely white or
completely black. Both of the ventral fins may be black, both white,
or one may be black and the other white.
A heterozygous
marble has a similar appearance to M/M, except that a larger area of
the body will be white. Generally, the amount of white increases some
in M/Gm, and increases further in M/g. However, there is not a
distinct demarcation between the amount of white for each genotype.
As
a result of selective breeding, some strains of marble will tend to
have more white than others. It is impossible to accurately
identify the genotype without either knowing the genetics of the
parents or doing a test cross. A test cross with a gold
angelfish can be used to verify the genotype of a marble. The
phenotypes of the offspring will identify whether one marble allele is
paired with another marble allele, a gold marble allele, or a gold
allele.
|
Test Cross with Gold to Determine Genotype of
a Marble |
|
If the parents have these genotypes: |
The offspring will have these phenotypes: |
|
M/M x g/g |
100% M/g (marble)
|
|
M/Gm x g/g |
50% M/g (marble)
50% Gm/g (gold marble) |
|
M/g x g/g |
50% M/g (marble)
50% g/g (gold) |
Silver Marble
A silver marble
is a heterozygous marble in which one marble allele is paired with one
wild type allele. The genotype is shown as M/+. The marble
and wild type alleles are co-dominant; the silver marble shows a
blending of the two traits. The angelfish will have a marbled
appearance. However, the coloration will be more muted, with
grayish silver instead of white. This phenotype is sometimes
also referred to as a barred marble because the stripes of the wild
type can sometimes be seen.
Factors
that Affect Expression of the Marble Phenotypes
Marble
is constant in its expression. Environmental conditions do not
change the phenotype. Marbles raised under a variety of
environmental conditions including different lengths of daily light
will always show the marble phenotype. The black coloration does
not fade when the fish is stressed, as it does in the stripes of a
wild type. In a silver marble, when the fish is stressed, the
stripes, if present, may fade, much as they do in a silver angelfish.
However, the black marbled areas will not fade.
Changes
in the Phenotype as the Angelfish Matures
The marble pattern
and coloration is evident in young fry.
Although the black and white
coloration is established in very young juvenile marbles, some subtler
but distinct changes occur as a juvenile matures into an adult.
The most obvious change is the development of horizontal striations in
any white stripes in the dorsal fin; these striations have blue
iridescent bands. The iridescence shows most intensely when the
angelfish is either exhibiting a territorial behavior or is preparing
to spawn. Some adult marbles may exhibit blue iridescence on
other parts of the body, such as a strip of blue iridescence on the
caudal peduncle, or small iridescent spangles on random parts of the
body. When an orange crown is present, it may be very light in
color or not apparent in a young juvenile, but the color will develop
and deepen as the angelfish matures.
Additional
angelfish phenotypes are formed from the blending of the effects of
non-wild alleles at two or more loci.
However all of the effects are generally subtle and the marble trait
will be the primary expression of each phenotype.
Interactions of Marble with Non-Wild Alleles at other Loci
The table below shows phenotypes that are formed from interactions
between marble and non-wild alleles at other loci.
|
Phenotypes resulting from Marble + Alleles at
other Loci |
|
Alleles: |
M/M, M/Gm, M/g |
M/+ |
|
Z/+, Z/Z |
[1] |
Zebra Marble [1] |
|
S/+ |
Marble Ghost
 |
(Silver) Marble Ghost |
|
S/S |
Marble Blushing
 |
(Silver) Marble Blushing |
|
Z/S |
[1] |
[1] |
|
Sm/+ |
Smokey Marble |
Smokey Marble |
|
Sm/Sm |
Chocolate Marble |
Chocolate Marble |
|
h/h |
Marble Halfblack [1] |
Marble Halfblack [1] |
|
a/a |
Albino Marble |
Albino Marble |
|
p/p |
Marble Pearlscale |
(Silver) Marble Pearlscale |
|
V/+ |
Marble Veil Tail |
(Silver) Marble Veil Tail |
|
V/V |
Marble Super Veil Tail |
(Silver) Marble Veil Tail |
Table Notes: [1]
Information not available on phenotypic expression of these
genotypes.
Authors
of this page have no information on the expression of marble genotypes
with zebra.
A marble
ghost will be virtually indistinguishable from a marble. A
marble blushing will exhibit pink blushing in the gill area as a fry
and young juvenile. The blushing may not be visible in the adult as
the gill cover become opaque. However, the fins will be devoid of any
horizontal striations and the tail will not show any lacey pattern.
Albino
and halfblack are recessive traits that only express when the allele
is present in double dose. Halfblack (h/h) is believed to express
when combined with marble genotypes, but no information is available
to confirm this.
Pearlscale is recessive and will only express when present in double
dose (p/p). Pearlscale does not modify the color or pattern of a
marble, but alters the shape of the scales so they are more reflective
of light, resulting in a silvery shine to the non-black areas of the
body.
Veil
is a partially dominant allele that results in a veil tail marble in single dose
(V/+), and a superveil in double dose (V/V).
Links
to additional information about the marble allele
Dr. Joanne Norton, FAMA: September 1988, Vol. 11, #9
Dr. Joanne Norton, FAMA: May 1989, Vol.12, #5
Dr. Joanne Norton, FAMA: May 1990, Vol. 13, #5
Dr. Joanne Norton, FAMA: December 1993, Vol. 16, #12
Approved by The Angelfish Society
Standards Committee on February 11, 2007.
W
