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Reprinted with permission from:
Dr. Joanne
Norton
Freshwater And Marine Aquarium
magazine
Blushing
Half-Black Gold Marble Angelfish
Photos and
Text by Dr. Joanne Norton
FAMA: December 1993, Vol. 16,
#12
Fig. 1: Male #1: Blushing gold
marble half-black.
Heterozygous for gold marble.
Fig. 2: Male #2: Blushing gold
marble.
Homozygous for gold marble.
Blushing
Half-Black Gold Marble Angelfish
Gold marble
angelfish that are heterozygous
(single dose) for marble are
less extensively pigmented that
gold marbles that are homozygous
(double dose) for marble
(Norton, 1988). That article
contained photos of both types.
The half-black
pattern is due to a single
recessive gene (Norton, 1989).
In that article there were
photos of various half-blacks,
including ghost half-black,
blushing half-black, and marble
half-black.
There are
numerous genetic types of marble
angelfish (Norton, 1990). It is
not known whether or not an
identical gene for marble is
present in marbles and gold
marbles. Another possibility is
that the gold marble has either
one or two chromosomes carrying
closely-linked genes for gold
and marble. This linkage could
have arisen as the result of a
chromosome crossover whereby the
gene for gold and the gene for
marble, which are known to be
alleles or closely-linked
(Norton, 1988), would end up on
the same chromosome instead of
separate chromosomes of the
pair. In any case, a gold marble
angelfish having only one
marble-containing chromosome has
the gene for gold on the other
chromosome of that pair.
A distinctive
marble phenotype results when
one chromosome is gold marble
and the other chromosome of that
pair is wild-type. This fish has
the marble pattern along with
vertical body stripes like the
stripes in a silver angelfish
(Norton, 1990). However, these
stripes are eliminated in such a
fish that also has the gene for
stripeless, which is an
incomplete dominant (Norton,
1971).
Fig. 3. Male #3: Blushing gold
marble.
Homozygous for gold marble.
Fig. 4. Male #4: Blushing gold
marble.
Homozygous for gold marble.
Fig. 5. Male #5: Blushing gold
marble.
Homozygous for gold marble.
Fig. 6. Female #6: Blushing gold
marble half-black.
Heterozygous for gold marble.
To find out
whether blushing gold marble
angelfish have more widely
distributed black markings in
homozygous (for marble)
individuals than in heterozygous
(for marble) fish, I first made
a cross to obtain some of each.
Both fish that I used for this
cross had one gold marble
chromosome paired with a
wild-type chromosome. Also, both
fish that had one dose of the
gene for stripeless and two
doses of the gene for
half-black. Their phenotype was
gold marble half-black.
(Fig.8).
The offspring
from the above pair included
some blushing (double dose of
the gene for stripeless) gold
marbles. Some of these blushing
gold marbles also had the
half-black pattern and others
did not, even though all of them
were known to be homozygous for
half-black because both of their
parents were homozygous for
half-black. Only the sparsely
marbled ones (heterozygous for
gold marble?) had the half-black
pattern. The more heavily
marbled ones (homozygous for
gold marble?) fish did not have
the half-black pattern. I then
made crosses with seven of these
blushing gold marbles to find
out whether the darker
individuals (also without
half-black) were indeed
homozygous for gold marble and
the lighter ones (all with
half-black pattern) were
heterozygous for gold marble.
This turned out to be the case
in all seven fish. The three
lightly marbled blushing gold
marble half-blacks were found to
be heterozygous for gold marble.
The four darkly marbled blushing
gold marbles (without
half-black) were found to be
homozygous for gold marble.
Fig. 7. Female #7: Blushing gold
marble half-black.
Heterozygous for gold marble.
Fig. 8. This female (also a male
like her) has a
wild-type chromosome paired with
a chromosome having
gold marble. Also, she is
homozygous for half-black
(and has the half-black pattern)
and heterozygous for
stripeless. They produced the
fish in Figs. 1-7.
I then made
crosses with seven of these
blushing gold marbles to find
out whether the darker
individuals (also without
half-black) were indeed
homozygous for gold marble and
the lighter ones (all with
half-black pattern) were
heterozygous for gold marble.
This turned out to be the case
in all seven fish. The three
lightly marbled blushing fold
marble half-blacks were found to
be heterozygous for gold marble.
The four darkly marbled blushing
gold marbles (without
half-black) were found to be
homozygous for gold marble. The
progeny counts were:
-
Male #1 (Fig. 1). Sparsely
marbled, with half-black
pattern. Mated to silver
female.
Progeny: 50 with marble
pattern, 69 non-marble.
Conclusion: this male has
heterozygous for gold marble.
-
Male #2 (Fig. 2). Heavily
marbled, without half-black
pattern. Mated to a silver
female.
Progeny: 102 with marble
pattern.
Conclusion: this male was
homozygous for gold marble.
-
Male #3 (Fig. 3). Heavily
marbled, without half-black
pattern. Mated to a silver
female.
Progeny: 315 with marble
pattern.
Conclusion: this male was
homozygous for gold marble.
-
Male #4 (Fig. 4) Heavily
marbled, without half-black
pattern. Mated to a silver
female.
Progeny: 83 with marble
pattern.
Conclusion: this male was
homozygous for gold marble.
-
Male #5 (Fig. 5). Heavily
marbled, without half-black
pattern. Mated to a silver
female.
Progeny: 129 with marble
pattern.
Conclusion: this male was
homozygous for gold marble.
-
Female #6 (Fig. 6). Sparsely
marbled, with half-black
pattern. Mated to a ghost
(heterozygous for stripeless)
half-black male.
Progeny: 72, including some
with and some without the
marble pattern.
Conclusion: this female was
heterozygous for gold marble.
- Female #7
(Fig. 7). Sparsely marbled,
with half-black pattern. Mated
to a silver male.
Progeny: 27 with marble
pattern, 29 without marble
pattern.
Conclusion: this female was
heterozygous for gold marble.
For a number
of years the inheritance of
half-black was not understood.
Then it was discovered that the
half-black pattern does not
develop in genetic half-blacks
that are raised in below-optimum
conditions (Norton, 1985). Prior
to this discovery, many
aquarists and fish farmers were
puzzled when no half-blacks were
produced by half-black parents.
Unexpected
results also could come from a
cross involving one parent that
is a genetic half-black
(homozygous for half-black) in
which expression of the
half-black pattern is suppressed
if the fish is also a homozygous
gold marble. Then a cross in
which only one parent has the
half-black pattern might produce
offspring in which 100% have the
half-black pattern. This is an
example of the advantage to the
fish breeder of knowing how a
certain gene can affect the
expression of another gene.
References
Norton, Joanne. Angelfish ---
breeding and genetics. The
Aquarium 6(10):34-41. 1971.
Norton, Joanne.
Half-black angelfish.
Freshwater and Marine Aquarium
8(8):18-23. 1985.
Norton, Joanne.
Gold marble angelfish.
Freshwater and Marine Aquarium
11 (9):88-90. 1988
Norton, Joanne.
Half-black combinations in
angelfish. Freshwater and
Marine Aquarium 12(5):26-28,
134. 1989.
Norton, Joanne.
Seven kinds of marble angelfish.
Freshwater and Marine Aquarium
13(5):127-135. 1990.
Notched - An
Angelfish Deformity
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