Basic genetics 2
Basic genetics 2
by morelia on Mon 2 Mar - 23:11
2. Co-dominance
Most traits in reptiles that are said to be inherited in a co-dominant (or co-dom) way are incorrectly labelled as such; they are actually inherited in a slightly different way, known as 'incomplete dominance'. Most people call it co-dom anyway and know to what traits it refers, and most people don't care about the fine details of the genetics, which is understandable as most don't have the inclination to learn more genetics than they have to!
Below is how incomplete dominance works, as this is actually the mode of inheritance for traits such as salmon hypo boas, arabesque boas, hypo Sonoran boas, Jaguar carpet pythons, tiger retics etc. At the very end of the post, I'll mention briefly (for the more patient, analytical people) the way in which true co-dominant inheritance works and how it differs from incomplete dominance.
If you breed an animal that displays an incompletely dominant (inco-dom) trait visually to a normal-looking animal, 50% of the offspring will display the inco-dom trait and the other 50% will appear normal. Note that this differs from the simple recessive trait where such a breeding would produce all normal animals that are 100% het for the trait. Because of this, inco-dom traits can propagate more of the same much faster (i.e. in one generation, whereas with the above breeding scenario and a simple recessive trait in would take 2 generations to produce more of the aberrant morph). Also notice how MORE offpsring will show the aberrant morph after one breeding (50%) than with simple recessive genetics after generations of breeding (25%).
A good example of this mode of inheritance is the Jaguar carpet python, a colour and pattern mutation of the Coastal carpet python. Breed one of these guys to a normal Coastal carpet and you will produce 50% Jags and 50% normal-looking offspring. As with most inco-dom traits, the 50% of offspring that do not show the aberrancy / morph are called 'normal siblings' (or 'sibs' for short) to denote that they are normal in appearance. Unlike hets in the simple recessive mode of inheritance, these normals will never be able to produce the inco-dom trait (Jags) if you breed two together; they do not carry any genes to produce it. HOWEVER, very often with inco-dom traits these normal-looking siblings are slightly brighter and more contrasting in appearance than true normal Coastals, and so the Jag influence does have a very slight influence on their appearance, but they do not inherit any ability to propagate the Jaguar morph.
'Super' animals
The inco-dom trait is interesting in that if you breed two visual animals together, you get a 'super' form which seems to acquire a 'double dose' of the abberant colours and / or patterning that the parents display. If you breed 2 Jaguar carpets together, you will produce 50% Jaguars, 25% normal sibs, and 25% of the super form, which is the Leucistic Jaguar carpet python. Such 'super' forms of inco-dom traits can be breath-taking - google super tiger retic or super salmon hypo boa and see for yourself!
How incomplete dominance resembles and differs from simple recessive traits
Because inco-dom traits have a super form, they are comparable to the simple recessive condition in that the super form (leucistic Jag) would be the equivalent to the 'homozygous recessive' condition i.e. very different to the wild type or normal snake, and the Jaguar form would be equivalent to the 'het' condition, because when you breed 2 together you produce something very different from the wild type. So a Jaguar carpet could be said to be a visual het for the leucistic carpet python, which would be the dominant form of the Jaguar gene. The main difference here is that the 'het' form (the Jag) is visually different from both the normal / wild type and also the super / homozygous recessive form, so there are therefore 3 different visual appearances here; with simple recessive genetics, hets are identical to normal animals (although there are a few exceptions to this). The ratios of offspring displaying the aberrant trait are also different from what you would get with a simple recessive trait.
Ratios
- breeding a visual het animal with a wild-type animal will produce 50% visuals and 50% normal siblings
- breeding 2 visual het animals together will produce 50% visual hets, 25% normal siblings and 25% of the 'super' form
- breeding the super form to a wild-type animal will produce all visual hets. No normal siblings are produced, hence why the 'super' form is called the 'dominant' form of the inco-dom gene.
.....note how these ratios differ from those of simple recessive traits. These ratios are how breeders determine the mode of inheritance of a new trait / morph through breeding trials.
What does all this mean in the real World?
If you want to acquire a morph that is inherited in this way, the best thing you can do is wait a few years! This is because inco-dom traits can be reproduced in one breeding and you get a higher %age of them per clutch / litter. This means that they will go from rare to common in a much shorter time-frame than simple recessive traits, so waiting a few years will allow the price to drop into an affordable range.
It also means that if you want to breed your own morphs without the hassle of working with normal-looking hets, inco-dom morphs offer a solution.
Co-dominance
To differentiate between this and incomplete dominance, you would have to breed the 'super' / dominant form with a wild-type animaland look at the offspring.
With incomplete dominance, breeding a dominant animal to a wild-type animal produces all visual hets.....so if you breed a super salmon hypo boa to a normal boa, you will produce all salmon hypos and no normal-looking boas. The offspring have an appearance that shows the influence of both parents, i.e. the genetics of both parents have been BLENDED to create the appearance of the offspring in this breeding.
With co-dominance, breeding a dominant animal to a wild-type animal produces offspring which exhibit traits from both their parents - not the 'blending' effect but rather some areas will resemble one parent and other areas the other parent.
Very few reptile traits are inherited in a true co-dom fashion, and so a clear example to use here involves flower colours.....with incomplete dominance, crossing a red flower to a white flower produces pink flowers (i.e. a blend of both parents); with co-dominance, crossing a red flower to a white flower will produce a red flower with white spots or stripes.
Most traits in reptiles that are said to be inherited in a co-dominant (or co-dom) way are incorrectly labelled as such; they are actually inherited in a slightly different way, known as 'incomplete dominance'. Most people call it co-dom anyway and know to what traits it refers, and most people don't care about the fine details of the genetics, which is understandable as most don't have the inclination to learn more genetics than they have to!
Below is how incomplete dominance works, as this is actually the mode of inheritance for traits such as salmon hypo boas, arabesque boas, hypo Sonoran boas, Jaguar carpet pythons, tiger retics etc. At the very end of the post, I'll mention briefly (for the more patient, analytical people) the way in which true co-dominant inheritance works and how it differs from incomplete dominance.
If you breed an animal that displays an incompletely dominant (inco-dom) trait visually to a normal-looking animal, 50% of the offspring will display the inco-dom trait and the other 50% will appear normal. Note that this differs from the simple recessive trait where such a breeding would produce all normal animals that are 100% het for the trait. Because of this, inco-dom traits can propagate more of the same much faster (i.e. in one generation, whereas with the above breeding scenario and a simple recessive trait in would take 2 generations to produce more of the aberrant morph). Also notice how MORE offpsring will show the aberrant morph after one breeding (50%) than with simple recessive genetics after generations of breeding (25%).
A good example of this mode of inheritance is the Jaguar carpet python, a colour and pattern mutation of the Coastal carpet python. Breed one of these guys to a normal Coastal carpet and you will produce 50% Jags and 50% normal-looking offspring. As with most inco-dom traits, the 50% of offspring that do not show the aberrancy / morph are called 'normal siblings' (or 'sibs' for short) to denote that they are normal in appearance. Unlike hets in the simple recessive mode of inheritance, these normals will never be able to produce the inco-dom trait (Jags) if you breed two together; they do not carry any genes to produce it. HOWEVER, very often with inco-dom traits these normal-looking siblings are slightly brighter and more contrasting in appearance than true normal Coastals, and so the Jag influence does have a very slight influence on their appearance, but they do not inherit any ability to propagate the Jaguar morph.
'Super' animals
The inco-dom trait is interesting in that if you breed two visual animals together, you get a 'super' form which seems to acquire a 'double dose' of the abberant colours and / or patterning that the parents display. If you breed 2 Jaguar carpets together, you will produce 50% Jaguars, 25% normal sibs, and 25% of the super form, which is the Leucistic Jaguar carpet python. Such 'super' forms of inco-dom traits can be breath-taking - google super tiger retic or super salmon hypo boa and see for yourself!
How incomplete dominance resembles and differs from simple recessive traits
Because inco-dom traits have a super form, they are comparable to the simple recessive condition in that the super form (leucistic Jag) would be the equivalent to the 'homozygous recessive' condition i.e. very different to the wild type or normal snake, and the Jaguar form would be equivalent to the 'het' condition, because when you breed 2 together you produce something very different from the wild type. So a Jaguar carpet could be said to be a visual het for the leucistic carpet python, which would be the dominant form of the Jaguar gene. The main difference here is that the 'het' form (the Jag) is visually different from both the normal / wild type and also the super / homozygous recessive form, so there are therefore 3 different visual appearances here; with simple recessive genetics, hets are identical to normal animals (although there are a few exceptions to this). The ratios of offspring displaying the aberrant trait are also different from what you would get with a simple recessive trait.
Ratios
- breeding a visual het animal with a wild-type animal will produce 50% visuals and 50% normal siblings
- breeding 2 visual het animals together will produce 50% visual hets, 25% normal siblings and 25% of the 'super' form
- breeding the super form to a wild-type animal will produce all visual hets. No normal siblings are produced, hence why the 'super' form is called the 'dominant' form of the inco-dom gene.
.....note how these ratios differ from those of simple recessive traits. These ratios are how breeders determine the mode of inheritance of a new trait / morph through breeding trials.
What does all this mean in the real World?
If you want to acquire a morph that is inherited in this way, the best thing you can do is wait a few years! This is because inco-dom traits can be reproduced in one breeding and you get a higher %age of them per clutch / litter. This means that they will go from rare to common in a much shorter time-frame than simple recessive traits, so waiting a few years will allow the price to drop into an affordable range.
It also means that if you want to breed your own morphs without the hassle of working with normal-looking hets, inco-dom morphs offer a solution.
Co-dominance
To differentiate between this and incomplete dominance, you would have to breed the 'super' / dominant form with a wild-type animaland look at the offspring.
With incomplete dominance, breeding a dominant animal to a wild-type animal produces all visual hets.....so if you breed a super salmon hypo boa to a normal boa, you will produce all salmon hypos and no normal-looking boas. The offspring have an appearance that shows the influence of both parents, i.e. the genetics of both parents have been BLENDED to create the appearance of the offspring in this breeding.
With co-dominance, breeding a dominant animal to a wild-type animal produces offspring which exhibit traits from both their parents - not the 'blending' effect but rather some areas will resemble one parent and other areas the other parent.
Very few reptile traits are inherited in a true co-dom fashion, and so a clear example to use here involves flower colours.....with incomplete dominance, crossing a red flower to a white flower produces pink flowers (i.e. a blend of both parents); with co-dominance, crossing a red flower to a white flower will produce a red flower with white spots or stripes.
morelia-
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Location: Norn Irn
Registration date: 2009-03-02
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