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Normal Greys and Splits
Bird Tracks


   Now you'll learn all about the most common cockatiel mutation, the normal grey, and its splits.

   Normal grey Punnet Squares are exactly what you've already been doing. The female is just XY, and the male XX. This is the "normal" genotype, meaning that when you strip away all the glitz and glamour of a tiel, you're left with XY and XX, the "normal" mutation. So, as you already know, when you cross a normal grey cock with a normal grey hen, you get:

X X X Y
X X X X
X Y X Y


   100% of the males will be normal greys, and 100% of the females will be normal greys. This square does not mean you'll get an equal number of males and females in every clutch, it simply supplies you with the ratio of mutations to sexes.

   That's all there is to normal greys! It's been pretty painless so far. Now we look at splits. Normal Greys can look like normal greys, and yet be split to something else. Half of that bird's genes are not the "normal grey" gene. In these cases, you can wind up with birds that are not normal greys in the nest. We'll start by explaining the Pearl mutation.

   We indicate the Pearl mutation by substituting the "normal" X with XP. This tells us that on the X chromosome, there is Pearl. So in a Punnett Square:

X XP X Y
   
   


   The above square tells us that the male is split to Pearl. Females can never be split to pearl. There are other mutations that females also cannot be split to, which we will go into later. Working out the above square:

X XP X Y
X X XP X
X Y XP Y


   This tells us that 50% of the males (XX) will be split to pearl, and that 50% of the females (XY) will be pearls. Again, the females can never be split to pearl. They will either display it, meaning they carry it, or they will not. They don't have another X chromosome that will outdo the XP, so the XP one is displayed. The normal X is always dominant over any split. The gene being carried on the X chromosome is referred to as a sex-linked mutation.

   So what if the female is a pearl, and the male is a normal grey? The female will be XPY, and the male will be XX. Let's see it in the Punnett Square:

X X XP Y
X XP X XP
X Y X Y


   So you can see that the females will all be normal greys, and the males will all be split to pearl.

   You can use the above examples with any sex-linked mutation (remember, these are the ones where the gene is carried on the X chromosome!). Sex-linked mutations are: pearl, cinnamon, lutino, and yellowcheek. Here's an example with lutino (we'll use XL as the lutino gene):

X XL X Y
X X XL X
X Y XL Y


   See how it is exactly like the first pearl example? All sex-linked mutations will follow that pattern.

   Now it's going to get tricky. How about crossing a pearl hen with a cock that is split to lutino? Remember FOIL (first, outside, inside, last!)!

X XL XP Y
X XP XL XP
X Y XL Y


   So we see that from this crossing, 50% of the males are split to pearl, and the other half are split to pearl and lutino. For females, 50% will be normal greys, and 50% will be lutinos.

Next Step: Sex Linked Mutations