Dominant Genes, Recessive Genes
How does that work?

The most common types of inheritance of budgie varieties are dominant genes and recessive genes, incomplete dominance and sex-linked genes. Here we are going to discuss a few of the simple dominant and recessive ones.  Lets start with a very brief recap of the information from the Budgie Genetics page. If this doesn't make sense to you please go back and read that page before you continue...budgie genetics can be confusing enough without missing half the information you need!

Basic Information Recap

- a budgie has two copies of each gene, one from each parent.
- each gene can have the original form (the wild type) and one or more mutated forms.
- if a budgie has two different forms of a gene it is called heterozygous for that gene, if it has two the same it is called homozygous.
- if a budgie is heterozygous for a particular gene, the one that the budgie looks like is said to be dominant, whilst the other one (which you can't see) is recessive.
- a heterozygous bird is usually referred to as 'dominant gene' split 'recessive gene'. ie. green split blue, which is written as green/blue.
- each gene is named after the effect of the mutated gene (eg. blue).
- each gene is represented by a symbol, usually the first letters of the genes name (eg. bl). The dominant form of the gene is is written in upper case, the recessive one is written in lower case.

Varieties With a Simple Dominant-Recessive Inheritance

Here is a list of the more common varieties with simple dominant - recessive inheritance.

* green - Bl

* Blue - bl1

* yellowface 1 - bl2

* yellow face 2 - blyf2

* goldenface - blgf

* grey - G

* recessive pied - r

* fallow (english) - f

* fallow (german) - g

So How Does Dominant - Recessive Inheritance Work?

Lets use punnett squares and the information we have learned so far to do some examples of dominant genes interacting with recessive genes.

I am going to use our trusty 'green budgie mated with a blue budgie' example again. It does not matter what shade of green or blue they are as we will cover that latter on the page about incomplete dominance.

punnet square for green x blue

So we will start with two birds, a homozygous green bird and a homozygous blue bird:

- Green = Bl/Bl
- Blue = bl1/bl1

Possible alleles: the green can only pass on 'Bl' to its offspring, and the blue can only pass on 'bl1'

The punnett square on the right shows the possible outcomes:

- 100% Bl/bl1 (green/blue), which will look green, of course, because green is dominant and blue recessive.... with me so far?

punnett square for green/blue x green/blue

So, can you ever get a blue bird from crossing two green birds? Yes! The next punnett square will show how. Lets do a cross between two green/blue budgies:

- Bl/bl1 (green/blue) x Bl/bl1 (green/blue)

Possible alleles:
- each green/blue bird can only pass on 'Bl' or 'bl1' to its offspring

The outcomes:

- 25% Bl/Bl = homozygous green (looks green)
- 50% Bl/bl1 = green/blue (looks green)
- 25% bl1/bl1 = homozygous blue (looks blue)

So you end up with 3/4 green and 1/4 blue offspring.

Lastly, what would happen if you pair a green/blue budgie with a blue budgie? Get out a pen and paper and see if you can work it out for yourself.... then check it with the punnett square on the right.

punnett square for green/blue x blue

The results would be:

- 50% Bl/bl1 = green/blue (looks green)
- 50% bl1/bl1 = homozygous blue (looks blue)

So if you cross a green budgie with a blue budgie and only ever get green chicks then you can be sure the green is homozygous. If you get some blue chicks then the green bird must be green/blue, carrying the blue gene.

What Now?

Now that you can do a basic punnet square, and understand the difference between dominant and recessive genes you can work out results for many matings. Lets do another example, a trickier one! How do we do a punnett square for two different genes at once? Like this...

grey green/blue x blue budgie:

Remember that a grey green budgie is a green one with the grey gene, adding a wash over the green.

So the genotypes are as follows:
- grey green/blue = Bl/bl1 G/g
- blue = bl1/bl1 g/g

At this point I should introduce a new piece of terminology that applies to dominant genes only. When a budgie has a dominant gene it shows as its phenotype, but you can't see if it has one or two copies of the gene.

double factor refers to a bird that has two copies of a dominant gene.
single factor refers to a bird that has only one copy of a dominant gene.

So in our example the grey green budgie is a single factor grey green.

Each parent needs to pass on one allele for each gene, the gene for body color and the gene for the presence of grey.

The possible allele combinations are:

- grey green/blue = Bl/bl1 G/g
- can pass on Bl G, or Bl g, or bl1 G, or bl1 g.

- blue = bl1/bl1 g/g
- can only pass on bl1 g.

So the punnett square looks like this:

Note that this punnett square is a different shape from the previous ones. The shape and size is controlled by how many combinations of alleles you have to work out. It is common to have 4 x 4 punnett squares giving 16 possible outcomes! However, for our example we get:

25% Bl/bl1 G/g - Grey Green/Blue
25% Bl/bl1 g/g - Green/Blue
25% bl1/bl1 G/g - Grey
25% bl1/bl1 g/g - Blue

So from this mating you have four possible phenotypes. If you had no understanding of budgie genetics this would be very confusing, and seemingly random! However, with a little knowledge it becomes much clearer....I hope. You can see how this understanding can help breed for the varieties and colours you like, for example from this mating you produced greys without using a grey parent!

I think that's enough examples of how dominant genes and recessive genes work. If you need more help, feel free to contact me!

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