Origin of the Coral Trait

We believe that the available data indicate that the coral trait is not the result of selective breeding. The coral trait first appeared in one of Peter Kahl's earliest albino litters, and its appearance was sudden – not the result of two, three, four generations of purposeful breeding toward a desired look. This information appears to, by definition, rule out selective breeding as a primary element of the genetics behind the coral trait.

It appears that the coral trait is not recessive. Breeding trials of coral albino to regular albino and to het albino have produced coral albinos. This outcome would not be possible with a recessive trait (except in the case of a sex-linked trait, but this does not appear to be the case with the coral trait as explained below). Note that this does not imply that the coral trait is necessarily some form of simple single-gene-mutation dominance.

It has been shown that het albino boas can possess and express the coral trait. Breeding trials of boas thought to be coral het albino to regular albino or het albino have produced coral albinos (the terminology “coral het albino” is used here based on our own nomenclature convention, which is explained in detail on our "The BoaMorph Approach to Coral Nomenclature" page).

Thus far, the coral trait has been observed and proven to occur only in boas that are Kahl-strain albino or het albino. The coral trait has not been observed in Sharp-strain albinos or het albinos. Also, to the best of our knowledge, the coral trait has not been proven to occur in “normal” boas (in boas that are not albino or het albino). For example, with a cross of two coral het albinos (the parental or P generation cross), 25 percent of the offspring will be normal (75 percent of the litter will exhibit the wt phenotype with respect to albinism; one in three of these will have the wt genotype with respect to albinism), but if the coral trait is independent of albinism, then regardless of the mode of inheritance one would expect at least some of those normal offspring to be coral. The proof would require breeding several of the wt phenotype offspring from this cross (the first filial, or F1 generation) to regular (not coral) albino boas and obtaining at least one litter in which no albinos were produced (indicating that the non-albino parent from the original litter is of the wt genotype with respect to albinism); these offspring (F2) would all be het albino “hypothetically-possible” corals. Many of these offspring would then have to be crossed back to each other and if a coral albino was produced (F3), then the coral trait would be proven to occur in the “normal” P1 boa (at least, the “normal” P1 boa would be the only known potential source of the coral trait). Also remember, of course, that after the birth of the F3 generation it could be as long as another year to 18 months before expression of the coral trait (if present) would begin, and even then one could end up with a large number of boas that look like they could be coral albinos, but in the absence of an obvious high‑expression coral albino it might be impossible to know for certain. It would require extreme dedication for anyone to expend the cage space, time and energy needed to complete such breeding trials.

It appears that the coral trait is not sex-linked. In mammals, the sex of an offspring depends on whether the sperm cell that fertilized the ovum contained an X or a Y sex chromosome (females XX, males XY). This XY system of sex determination is referred to as male heterogameity. The genes of a sex‑linked trait reside on the sex chromosomes, and recessive sex-linked traits will be expressed more frequently in males because the recessive allele needs only to be present on the X chromosome and not the Y chromosome (hemizygous). One example of such a trait is a particular form of color blindness in humans that is sex-linked recessive, and thus is far more common in men. Also, Thomas Hunt Morgan’s recessive white-eyed male fruit flies, when crossed with female homozygous dominant red-eyed fruit flies, yielded a 3:1 ratio of red:white eyes in the offspring, and all of the flies with white eyes were male (half the offspring are male, and half of those have white eyes, hence the 3:1 ratio of red:white eyes). All snakes use a similar system of chromosomal sex determination, except that the roles are reversed. In this system of female heterogameity, the sex chromosomes are designated Z and W, and the sex of an offspring is determined by which sex chromosome is present in the ovum rather than in the sperm that fertilized it (females ZW, males ZZ). Regardless, there does not appear to be any connection between the inheritance or expression of the coral trait and the sex of the offspring.

Dominance, incomplete dominance, co-dominance, and polygenic phenotype theory are all plausible as the mode of inheritance for the coral trait, though some of these appear more reasonable than others. However, it would be pointless to delve into any deeper a discussion of these possibilities without clear examples and definitions of these terms that are so often misunderstood and misused. So, unfortunately, further discussion will have to wait until we are able to complete and post our upcoming Genetics Glossary.

A high-yellow Groovy-Line Coral Albino born here at BoaMorph on New Year's Day, 2004.

Multiple alleles will also be discussed further after our Genetics Glossary is completed. As a sneak preview into this subject, consider the example of the ABO system of human blood type. This system involves three alleles: A, B and O. O is recessive with respect to both A and B, whereas A and B exhibit co‑dominance. So, a person who is AA or AO exhibits the blood Type A phenotype. Similarly, a person who is BB or BO exhibits the Type B phenotype. A person who is double recessive OO exhibits the Type O phenotype. Finally, a person who is AB exhibits the Type AB phenotype, in which both A and B antigens are produced (with co-dominance, both alleles of a gene are expressed; both alleles produce an effective product).

Another interesting consideration with regard to the coral trait is linkage. Linkage refers to genes that are inherited together on the same chromosome, which is not known to be the case with albinism and the coral trait, but it is interesting to consider nonetheless. Three inheritance patterns are possible: non‑linkage, partial linkage, and complete linkage. Given two loci on one chromosome, a typical deviation from expected ratios is the occurrence of less than expected numbers of recombinants . Linkage occurs because two loci found on the same chromosome may be separated only via molecular recombination, and molecular recombination is not as efficient a means of genetic recombination as independent assortment. That’s a mouthful. For now, we’ll simply note that linked alleles do not obey Mendel’s laws (i.e., they do not produce the familiar Mendelian genotype and phenotype ratios). We’ll save the rest of this discussion until after our Genetics Glossary is completed.