# How do you represent a co-dominant gene in a punnet square?



## tom12349333 (Sep 30, 2009)

Just doing some homework on genetics and I'm confused as to whether or not there's a specific way to represent a co-dom gene? 

eg with leo's - 

Normal - Dominant (N)
Albino - Recessive (a)

N N
a Na Na
a Na Na

So if a dominant gene is represented with a single capital letter, a recessive with a single lower case and a het a combination of the two how do you write a co dom gene? 
Thanks!


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## ilovecornsnakes (Apr 4, 2008)

wouldn't it just be 2 different capital letters?
if i've understood what your asking

. . A . b
C. CA Cb
d. Ad bd

with CA being co-dominant, Cb & Ad being dominant with recessive het, and bd being a double recessive gene

if i've made a mess sorry and hope someone else with more understanding can help (i can follow maths, not genetics)


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## paulh (Sep 19, 2007)

Codominant mutant genes are represented by an upper case letter. Same as for dominant mutant genes. Unfortunately, there are only two cases. It would help if there were three cases.

Internationally accepted symbol for wild type or normal gene is +. Most herpers use an N character for normal, though. The + character is better because then we can use "N" for a mutant gene.

P = pastel in royal pythons. Codominant to normal gene
+ = normal alternative to pastel mutant gene

a = albino in royal pythons. Recessive to normal gene
+ = normal alternative to pastel mutant gene

Ps = pinstripe in royal pythons. (Can't use P because that is already in use. So we use two characters to make a unique symbol for pinstripe.) Dominant to normal gene
+ = normal alternative to pinstripe mutant gene

// = a pair of chromosomes. One member of a gene pair is in one chromosome, the other member of the gene pair is in the same location in the other chromosome. (// is optional. It helps make a long genotype readable but is seldom used in genetics texts.)

Codominant mutant gene:
P//P = two pastel genes = homozygous pastel genotype, which produces the super pastel phenotype (appearance)
P//+ = pastel and normal genes = heterozygous pastel genotype, which produces the pastel phenotype (appearance)
+//+ = normal genotype, normal phenotype

Recessive mutant gene:
a//a = two albino genes = homozygous albino genotype, which produces the albino phenotype (appearance)
+//a = normal and albino gene = heterozygous albino genotype, which produces the normal phenotype (appearance)
+//+ = normal genotype, normal phenotype

Dominant mutant gene:
Ps//Ps = two pinstripe genes = homozygous pinstripe genotype, which produces the pinstripe phenotype (appearance)
Ps//+ = pinstripe and normal gene = heterozygous pinstripe genotype, which produces the pinstripe phenotype (appearance)
+//+ = normal genotype, normal phenotype


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## bothrops (Jan 7, 2007)

As Paul has shown, it can get a little tricky. What I tend to do is use a capital letter to code for the gene and then a superscript letter to define it. This isnt easy to show on these 'text only' forums, so I've done it in word and screen grabbed it!

The advantage of using this is you can also cover multiple alleles.






























You can write the same thing in plain text but it makes it more complicated. The lesser for example would be coded as " C^+//C^L "

Hope this helps!


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## paulh (Sep 19, 2007)

Tonight's connection is too slow for graphics. I can't see what Bothrops posted. 

For your own private use, any symbolism is acceptable as long as you make a key of definitions. Various bodies have more or less standardized genetic symbolism for their own particular species. For easiest communication with others, it helps to follow the symbolism rules for one of the more commonly studied species. I mostly follow the rules for rats and mice. Because I learned genetics while working with mice, and there are more geneticists working with mice and rats than working with all other nonhuman vertebrates put together.

MGI-Guidelines for Nomenclature of Genes, Genetic Markers, Alleles, & Mutations in Mouse & Rat
See section 3.1 for the parts herpers would use most.


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## eeji (Feb 22, 2006)

I use the same method as Bothrops with a locus identifier then either + or letter(s) in superscript to define which allele, using lower case for recessive and upper for codominant and dominant.


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