4.4 The Visual Grey

We have talked about the grey gene and its effect on a green bird. A single grey gene gives a green bird a grayish tone and changes the color to grey-green. Two grey genes have the same effect and the bird shows the same grey-green color as with a single grey gene. If a blue bird (two copies of the blue gene) also carries one or two copies of the grey gene it shows a grey color instead of blue and is called a visual grey. A visual grey is therefore not a primary mutation but actually a combination of the grey and blue mutations.

We will now look at how we may express this in standard genetic notation and use this notation to predict outcomes of birds carrying one or two copies of these genes. When dealing with multiple mutations in a single bird we must express all relevant genes in the standard notation. Following are some examples

A visual single factor (SF) Grey bl/bl, G+/G
A visual double factor (DF) Grey bl/bl, G/G
A grey green (SF) split to blue bl+/bl, G+/G
A grey green (DF) bl+/bl+, G/G

As shown above when a bird carries multiple mutations we simple list all the pairs of genes separated by a comma. Let’s move one step further and see how we can construct a Punnett square for a pair of birds carrying two mutations. Our sample pairing is a grey-green (SF) split to blue (bl+/bl, G+/G) paired to a SF visual grey (bl/bl G+/G). Each bird must contribute one gene from the two pairs of genes blue and grey. There are 2 possibilities for the mother she can give bl and G+ or bl and G. There are 4 possibilities for the father. He may give bl+ and G+ or bl+ and G or bl and G+ orbl and G. We put these values in the Punnett square. Combining the genes gives us the following table.




To summarize, we get 
12.5% Green split Blue
25% Grey-Green (SF) split Blue
12.5% Grey-Green (SF) split Blue
12.5% Blue
25% Visual Grey (SF)
12.5% Visual Grey (DF)

Don’t get scared by the apparently complicated diagram. You will not need to make many of these by hand. There are calculators that will do the calculation for you (Chapter 5). However, you must understand how multiple genes come together to give different outcomes.

Homework
Try this pairing
SF Grey Green split blue X DF Visual Grey

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