4.3 The Grey Gene

The Grey Gene
We will now talk about the grey gene. The grey gene effects the appearance of melanin (blue/black pigment) in the feathers and gives the bird a grey appearance. This gene is dominant to the normal and therefore only a single gene is enough to cause a change in the visual appearance. We will use the symbol G to denote the grey gene. G+/G means that the bird has one grey gene and one Normal (G+) gene. Such a bird would appear grey green. A bird with two copies of the grey gene will be denoted by G/G. This bird also appears grey green and looks exactly the same as the bird with only one grey gene. When only one copy of the gene is sufficient to affect the appearance of the bird and a second copy has no further effect it is called complete dominance. A bird with one copy of the dominant gene is called a single factor (SF) and a bird with two copies of the dominant gene is called a double factor (DF) bird.

Let us go back to the Punnett squares method of calculating genetic outcome and look at some examples.
Normal Cock X grey green Hen

Here we see that 2/4 or ½ the birds are G+/G+ or Normal Green and the other half are G+/G or Grey Green. Since the grey gene is dominant the bird shows grey even though there is only one copy of the gene present.

Now let us look at a double factor grey green paired to a normal
Double factor Grey Green (G/G) X Normal (G+/G+)
Here we see that all chicks produced are G+/G or single factor grey green.

If you have absorbed the above you are probably wondering that if G+/G is grey green and G/G is also grey green what genes does a visual grey bird (not green) have? A blue bird with the grey gene is a visual grey. We write this in the genetic notation as bl/bl, G+/G. We will discuss this further in the next episode.

What do we get if we pair up two birds both single factor grey green?


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