Why is Pinkie possible

[LucasB 196]

You probably wondered how a bright pink pony came from a family of dull, gray ponies. I think this is due to a recessive gene in the family. A recessive gene is expressed only when both alleles (pair of corresponding genes) are recessive. When a recessive gene is paired with a dominant gene, only the dominant gene is expressed. 

Let's call the pink pony gene a (lower case for recessive), and the gray pony gene A (upper case for dominant)

Therefore, Pinkie must have the genotype aa to have a pink phenotype. That means both parents have the genotype Aa since that is the only way the parents can both produce an offspring with aa and also not express the a gene themselves. Pinkie's sisters would have either Aa or AA, but it is impossible to know which one.

It is also possible that the coat color is sex linked, meaning the gene for coat color exists in the sex specific chromosome of each pony. The mother contains two X chromosomes while the father contains an X and a Y. The mother passes one of her two X chromosomes, while the father pass on their Y to sons and X to daughters. This means that if a certain recessive gene exists on one of the X chromosome on the mother and the X chromosome of the father, there is a 50% chance it is passed onto an offspring. The possible genotypes of the offspring would be Aa with 50% chance and aa with 50% chance.

Since the sample size is too small, it is impractical to run a Chi Square goodness of fit test on these two scenarios, and would produce a statistically insignificant result, so based on the percentages, it is safe to say that both are likely to be the reason Pinkie is pink. 

[Scrubbed user 3,416]

Or a genetic mutation.

Edited June 7, 2018 by Vulon Bii

[SharpWit 2,614]

As much as I love this sort of stuff, when something regards Pinkie Pie, one question is already too many.

[Venomboa 7]

Because show. I don't question it that much, but if you want a similar example...Ty Lee from Avatar the Last Airbender, she wanted to be different.