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The Location of the Genes
July1982: Vol.5, # 7-Part III

Published with permission from BowTie Inc., publisher of FishChannel.com.

 

In Parts 1 and 2, I discussed the inheritance of mutant genes that affect the color of aquarium-bred angelfish. In this article I shall add information on the location of these genes. This additional knowledge is essential in order to know which gene combinations are possible and also to enable you to predict correctly the outcome of crosses involving more than one mutant gene.

The angelfish's chromosomes (containing the genetic material) are in pairs, one chromosome of each pair having come from each parent. Each gene occurs at a specific location, called locus (plural, loci), on the chromosome. Variations of a gene are called alleles. Only one allele occurs at a locus; another allele of that gene can occur at the same locus on another chromosome.

Tests for Allelism

Black Angel (1 dose of dark and 1 dose of marble.)

Black Angel. (1 dose of dark and 1 dose of marble.)

A marble female (having two doses of marble), mated to a black lace male (one dose of dark), produced 23 marble and 22 black (one dose of marble and one dose of dark). This type of black angelfish, called marble lace (Norton, 1971), has a marbled pattern on the body that can be seen by shining a flashlight on the fish. A true black (two doses of dark) has faint vertical body stripes that can be seen by using a flashlight.

When a wild-type (silver) female was mated to a marble lace male, the offspring were 48 black lace and 46 marble. Since there were no wild-type offspring, I concluded that the genes for dark (D) and marble (Dm) act as alleles. In other words, these genes are at the same locus.

A wild-type female and zebra lace male (one dose each of dark and zebra) produced 9 wild-type, 6 black lace, 4 zebra, 5 zebra lace. It is concluded that the genes for dark (D) and zebra (Sze) are not alleles since the above cross produced some wild-type.

Black Angel. (1 dose of dark and 1 dose of new gold.)

A new gold female and true black male (D/D) produced 100% black, which were not as deeply pigmented as the true black. This type of black (one dose of new gold and one dose of dark) has a slight bronze cast on the body and evident vertical bars. Crossing two of these blacks resulted in an F2 consisting of 62 new gold and 200 black, no black lace or wild-type. Also a new gold female and black male (whose parents were new gold and true black) gave 214 black and 207 new gold offspring. Thus the gene for dark (D) and new gold (dng) behave as alleles.

Black lace were obtained by mating true black and Hong Kong gold. These black lace, which carried the recessive gene for Hong Kong gold (see Part 2), produced an F2 of 29 wild-type, 49 black lace, 12 black, 4 Hong Kong gold. It is concluded that the genes for dark (D) and Hong Kong gold (hg) are not alleles since some wild-type offspring were produced.

Numerous blushing marble were obtained from a blushing crossed with a fish that had one dose each of stripeless and marble (having come from a blushing x marble cross). Since a blushing marble would have to have one gene for marble and two genes for stripeless, it is deduced that the genes for stripeless (S) and marble (Dm) are not alleles.

A smokey female, crossed with a male having one dose of marble, produced 79 wild-type, 157 marble, 86 smokey. Some of the marbles were suspected of having one dose of smokey because they exhibited one or more of these smokey features: (1) black mouth, (2) black-tipped dorsal fin, (3) gray in the white streaks in the outer part of the caudal fin. Two such males were tested for smokey by mating them to wild-type females. This produced: male #1: 126 wild-type, 269 marble, 123 smokey; male #2: 27 wild-type, 47 marble, 21 smokey. Not only was smokey present in the tested marble males but the genes for marble (Dm) and smokey (Sm) did not act as alleles since the crosses produced some wild-type offspring.

A male having one dose each of marble, zebra and smokey was mated to a wild-type female, producing 37 wild-type, 136 marble (including marble with zebra and/or smokey), 34 zebra, and 59 smokey (including zebra-smokey). Zebra-smokey looks like zebra until the stripes disappear as the smokey pattern develops. Since there were wild-type offspring, it is concluded that the genes for marble (Dm) and zebra (Sze) are not alleles.

1 dose of marble and 1 dose of new gold.

A marble female was mated to a new gold male, producing 241 wild-type and 217 marble. One of the marble F1 males, mated to a new gold female, produced 105 marble and 111 new gold. Since no wild-type offspring were produced, it is concluded that the genes for marble (Dm) and new gold (dng) act as alleles.

Since (1) the genes for dark and marble behave as alleles, and (2) the genes for dark and Hong Kong gold do not act as alleles, it follows that the genes for marble (Dm) and Hong Kong gold (hg) are not alleles.

A smokey male was tested and found to have one does of stripeless since, when mated to a wild-type female, he produced wild –type, smokey and stripeless offspring. Since there were some wild-type offspring, it is concluded that the genes for smokey (Sm) and stripeless (S) are not alleles.

1 dose of Zebra and 1 dose of stripeless.

A female with one dose of zebra, mated to a blushing male, produced all stripeless offspring, some of which had more black blotches on the body than I had ever seen on fish with one does of stripeless but without zebra. When the ones with increased splotching matured, their dorsal fins had an increased number of light-colored horizontal bars (compared with wild-type), a zebra characteristic. One of these that was suspected of having one dose each of zebra and stripeless was tested by mating him to a wild-type female. From the results, 188 stripeless and 220 zebra, it is concluded that the tested fish did have one dose each of stripeless (S) and zebra (Sze) and that these genes behave as alleles.

A blushing female, mated to a Hong Kong gold male, produced 100% stripeless, non-gold offspring. The F2 included some each of blushing, Hong Kong gold blushing, stripeless, Hong Kong gold and wild-type. It is concluded that the genes for stripeless (S) and Hong Kong gold (hg) are not alleles, since wild-type appeared in the F2 and since Hong Kong gold blushing would have to have two doses of each of Hong Kong gold and stripeless.

Naja gold beginning to lose the black pigment on its mouth.

Since (1) stripeless and zebra act as alleles and (2) stripeless and smokey are not alleles, then it follows that the genes for smokey (Sm) and zebra (Zse) are not alleles.

A smokey female x new gold male produced smokey and wild-type offspring. One of the F1 smokey males was mated to a new gold female, giving 91 wild-type, 80 smokey, and 156 new gold. This fits the expected ratio (1 wild-type: 1 smokey: 2 new gold), if the smokey pattern is not expressed in a fish having two doses of new gold. Therefore, half of the 156 new golds were assumed to carry the gene for smokey. Further evidence that new gold, in double dose, blocks development of the smokey pattern was obtained by mating smokey parents, both of which came from smokey female and new gold male. These produced 71 smokey, 33 chocolate (double dose smokey, see Part 1), 42 new gold, 32 wild-type. These numbers fit the expected ratio (6 smokey: 3 chocolate: 4 new gold: 3 wild-type), if the smokey pattern is not expressed in the presence of double-dose new gold. Since each of the spawns (from smokey male carrying new gold x new gold female, and from smokey parents each having one dose of new gold) produced some wild-type offspring, it is concluded that the genes for smokey (Sm) and new gold (dng) are not alleles.

Since (1) zebra and stripeless behave as alleles and (2) stripeless and Hong Kong gold are not alleles, is is deduced that the genes for zebra (Sze) and Hong Kong gold (hg) are not alleles.

It has already been stated that new gold in double dose blocks expression of the smokey pattern. The same is true for new gold zebra, which also has no black body pattern. A zebra female that had one dose of new gold was mated to a new gold male, producing 103 new gold (including new gold zebra), 57 zebra, and 73 wild-type. The genes for zebra (Sze) and new gold (dng) are not alleles, since numerous wild-type were produced. Although new gold zebra has no black pattern on the body and fins, in juveniles it can be distinguished from new gold by its three very faint vertical body stripes (paler than the rest of the body) instead of two pale stripes in new gold without zebra. An adult gold zebra has approximately 12 light-colored horizontal bands in the dorsal fin, while a new gold has about 7 or 8.

Since (1) new gold behaves as an allele of dark and (2) Hong Kong gold is not an allele of dark, it follows that the genes for Hong Kong gold (hg) and new gold (dng) are not alleles.

Summary of the Genes
All of the major color patterns in today’s aquarium-bred angelfish are due to seven mutant genes if we eliminate from discussion the Naja gold, which is no longer of commercial importance and is difficult, if not impossible, to locate. These seven genes occur at four loci, as follows:
Locus #1: Hong Kong gold (hg), recessive to wild-type
Locus #2: smokey (Sm), dominant to wild-type
Locus #3: stripeless (S), dominant to wild-type; zebra (Sze) dominant to wild-type
Locus #4: dark (D), dominant to wild-type; Marble (Dm), dominant to wild-type; new gold (dng), recessive to wild-type

Practical Applications
Since in most cases in angelfish has only two doses of a set of alleles, certain limitation exist in gene combination. For example, there is no advantage in trying to get an angelfish with one dose of marble and two doses of new gold, since and individual has only two doses, not three, of this set of alleles. The possible combinations of the multiple alleles dark, marble and new gold are:
(1) one dose of dark
(2) one dose of marble
(3) one dose of new gold
(4) two doses of dark
(5) two doses of marble
(6) two doses of new gold
(7) one dose of dark and one dose of marble
(8) one dose of dark and one dose of new gold
(9) one dose of marble and one dose of new gold

The gene for new gold, in double dose, blocks expression of smokey and zebra. In contrast, one dose of new gold enhances the expression of both dark and marble, resulting in an increased black pigmentation.
There are three genotypes of marble angelfish:
(1) two doses of marble (Dm/Dm)
(2) one dose of marble (Dm/d+)
(3) one dose of marble and and one dose of new gold (Dm/dng).
As was discussed earlier (Part 1), the double-dose marble breeds true but is slow growing and less vigorous than the single-dose marble. I also explained in that article how to obtain spawns of 100% single-dose marble, by crossing wild-type with double-dose marble

An angelfish with one dose of marble and one dose of new gold, which also is a good commercial type (perhaps better than single-dose marble because of it jet black markings), is also vigorous. Because of individual variation, double-dose marble may be difficult to distinguish from the marble-new gold type. However, if you can observe an entire spawn of only one type you can tell them apart because most double-dose marbles are mostly black and have very little white area (the dark areas are jet black as in the marble-new gold type). In comparison, most fish with one dose each of marble and new gold have larger white areas. The dark pattern of a single dose marble is a mixture of black and gray, not as striking as the pattern of the marble-new gold type.

To raise 100% marbles of either single-dose marble or the marble-new gold type, you need a double-dose marble for one parent. See Part 1 for instructions to obtain double-dose marble. The two crosses to obtain 100% of the best commercial marbles are:
(1) double-dose marble x wild-type (silver): 100% single-dose marbles
(2) double-dose marble x new gold: 100% marbles with jet black pattern

The true black (double-dose dark) angelfish breeds true but is slow-growing and unsatisfactory for commercial production. A fish that is just as black but that is much more vigorous is the one that has one dose of dark and one dose of marble (D/Dm). To get 100% of this type of black, which has a faint marbled body pattern under strong light, cross a double-dose marble female with a true black male.

Another satisfactory black, as far as vigor is concerned, is that one that has one dose of dark and one dose of new gold (D/dng). The body of this fish is somewhat brassy and the body stripes are more obvious than in a true black. To get 100% of this type, cross a new gold female with a true black male.

An aquarist is likely to buy whatever type of black angelfish is available, which today in most cases will be either marble lace (D/Dm), or dark-new gold (D/dng), and raise them for breeders. Using marble lace parents, you will get about 75% black (including 25% true black and 50% marble lace), and about 25% double-dose marble. If dark-new gold parents are used, you will get about 75% black (including 25% true black and 50% dark-new gold), and about 25% new gold. There are disadvantages in using these crosses to obtain black angelfish. (1) You will not get 100% blacks and you will need to sort. (2) The true blacks will grow more slowly than the other blacks and will reach selling age later. If you happen to buy black angelfish that are different genetically but not true black, you could own breeders in which one is the dark-marble type and the other is the dark-new gold type. If these types are crossed, they would produce 25% true black, 25% black (dark-new gold), 25% black (marble lace), and 25% marble. This spawn also would require sorting.

As was discussed in Part 1, crossing a true black with a wild-type (silver), produces 100% black lace offspring. You will not get this result if the black parent is not true black (two doses of dark). Crossing a wild-type with a black that has one dose each of dark and marble will produce 50% black lace and 50% marble. Or, if you cross wild-type with a black that has one dose each of dark and new gold, you will get 50% black lace and 50% wild-type.

A blushing angelfish (two doses of stripeless) has very little black pattern on the body. Yet, the marble pattern develops when present with blushing, so a blushing marble angelfish (having the marble pattern along with red gill areas in juveniles), is possible (Norton, 1971). Knowing that the genes for stripeless and zebra act as alleles, you can save yourself the trouble of trying to get a blushing zebra angelfish. The possible combinations of these two genes are:
(1) one dose of stripeless
(2) two doses of stripeless
(3) one dose of zebra
(4) two doses of zebra
(5) one dose of stripeless and one dose of zebra

Number 5 above differs from number 1 by having more black markings, and also more green body color in the adult.

Genotypes
The genotypes listed below are for the angelfish discussed to date:

Hong Kong gold = hg/hg
Smokey = Sm/+
Chocolate = Sm/Sm
Stripeless (Ghost) = S/+
Blushing = S/S
Zebra = Sze/+ or Sze/Sze
Zebra, one dose stripeless = Sze/S
True black = D/D
Black lace = D/+
New gold-dark = (black) (D/dng)
Light marble = Dm/+
Dark marble = Dm/Dm
Marble with jet black pattern = Dm/dng)
New gold = dng/dng
Zebra lace = Sze/+ D/+

 

Literature Cited
Norton, Joanne, Angelfish – breeding and genetics.
The Aquarium 6 (No. 10) 34-41. 1971

 
 
 
 
 
 
 
 
 
 
 
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