| T O P I C R E V I E W |
| eeji |
Posted - 09/02/2011 : 20:25:13
There seems to be lots of confusion around about the different modes of inheritance for morphs and also what heterozygous and homozygous is, so this will 'hopefully' explain it simply.
Each morph sits at its own locus (place) on the chromasome and each locus has a pair of alleles. An allele is a 'version' of a gene, either normal or mutated eg. at the anerythtristic locus there are two versions (normal and anerythristic) and at the amelanistic locus there are three (normal, amelanistic and ultra).
If a pair of alleles are identical (both normal or both the same mutation) this is homozygous, and if they are different (normal/mutation or mutation 1/mutation 2) then this is heterozygous.
In the examples below, each different letter represents an individual allele. Upper case is used for dominant or codominant and lower case for recessive. The + symbol represents a normal, unmodified allele.
Recessive to normal (eg. anerythristic cornsnakes):
++ - normal - looks normal
+n - heterozygous - looks the same as normal
nn - homozygous - looks different to normal and heterozygous
Codominant with normal (eg. mack/super snow leopard geckos):
++ - normal - looks normal
+M - heterozygous - looks different to normal
MM - homozygous - looks different to normal and different to heterozygous
Dominant over normal (eg. tessera cornsnakes):
++ - normal - looks normal
+T - heterozygous - looks different to normal
TT - homozygous - looks different to normal but the same as heterozygous
Where there are more than two possibilities for each allele things get interesting. If we take the amelanistic locus in cornsnakes as an example there are three possible alleles, normal amel or ultra. Amel and ultra are both recessive to normal but codominant to each other.
++ - normal - looks normal
+a - heterozygous amel - looks normal
+u - heterozygous ultra - looks normal
aa - homozygous amel - looks different to normal, het amel, het ultra
uu - homozygous ultra - looks different to normal, homo amel, het amel, het ultra
au - heterozygous amel/ultra - looks different to all the above (this is the 'ultramel' morph)
The motley cornsnake locus also has three different allele possibilities (normal=+, motley=m, stripe=s)but the dominance is slightly differnt to the above example. Both motley and stripe are recessive to normal, but motley is dominant over stripe. The outcomes therefore would be the same as above except for the very last pair. In this case ms (het motley/stripe) would look the same as mm (homozygous motley), and the stripe allele has no influence on the pattern whatsoever contrary to popular belief - ie. a motley that has some striping does not mean it is het stripe.
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| 5 L A T E S T R E P L I E S (Newest First) |
| simonw |
Posted - 10/02/2011 : 12:29:24
Thanks for presenting that. Very useful. |
| herriotfan |
Posted - 10/02/2011 : 10:05:08
I quite agree Newbie....sticky mods please!!  |
| Newbie |
Posted - 09/02/2011 : 23:02:37
That would be fantastic, I love genetics but no so hot on it all really! Much more for me to learn  this should be a sticky because the guides really concise |
| eeji |
Posted - 09/02/2011 : 22:01:48
there aren't that many in corns, some morphs have some degree of sexual dimorphism in their colours (eg. male lavenders are often pinker than females, but not always). The comlete genome hasn't been mapped, so theres lots of things unknown yet.
There is a project in the planning stages at Bangor University to map a snake, hot favourites at the moment are corn or royal so fingers crossed they choose corns! :D The only problem they'll have with corns seems to be the amount of inbreeding and inter species breeding may give false results so will need doing again with a wild caught individual from the USA to compare results (or do this first if they can scrape enough cash) |
| Newbie |
Posted - 09/02/2011 : 21:16:11
This is a great guide! I have a basic understanding of human genetics, but where there are several mutations and the allele's interact differently with co-dominance things can get really complex!
I know humans often show sex-linked genetic traits but not sure whether this happens with snakes, what gender defining chromosomes do they have? |
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