Nan's No-Tech Genetics

page two

There is one pair of chromosomes that is different from the others. This pair is the sex chromosomes. Sex chromosomes come in two types: One type is the regular length and the other type is really short.

In birds, the females have one regular length sex chromosome and one of the short ones. Males have a pair of the regular-length ones.

You can see that a lot of the genes on the regular length sex chromosome aren't going to have a partner on that little short chromosome. That means nobody to disagree with. So the genes on the regular length chromosome (I'm going to call it the X chromosome) with no partner on the short chromosome will get to have their way.

But that's only in the girls. The boy birds have two X chromosomes that have to argue it out like always. It's just the girl birds who get a break, and only on that one chromosome pair. But it's REALLY useful to know which genes live on that X chromosome!

In budgies, here are some of the genes that live on the X chromosome: the genes for ino (lutino and albino), cinnamon, and opaline.

Cinnamon is when the (normally black) markings on the bird are brown instead of black. Opaline is when those markings are on the bird's wings, but not on the head or back.

In cockatiels, the genes for ino, cinnamon, and pearl are on the X chromosome. (We will use budgies for our examples, though.)

So what? Ok, let's see what happens if a female bird has one gene for lutino: there's no gene to disagree with it, and so the lutino gene wins. So if a female HAS a lutino gene, you will see she's lutino.

If a male has one lutino gene, what happens? It is recessive, disagrees with its dominant partner-gene, and loses. So a male can HAVE a lutino gene and still look normal green. He has to have two lutino genes before he can look yellow. Some of those green males running around out there have a "hidden" lutino gene.

The same thing goes for cinnamon and opaline.

When people argue, we say they are split on an issue. When a pair of genes disagree with each other, we say the bird is "split". In the example above, the poppa with one lutino gene and one green gene is "split to lutino".

So how does a baby bird get its genes? (This is why the chromosomes come in pairs.) To make a baby, the parents' chromosome pairs split up. Momma gives the baby one chromosome from each pair. Poppa give the baby one chromosome from each of his pairs. That makes the new pairs of chromosomes in Baby.

In Baby, there are new gene pairs... To make each pair of genes, Baby got one gene from Momma and one gene from Poppa. These new gene pairs argue it out to decide what Baby should look like.

Now, lets look at those sex chromosomes again. Momma bird has to give one of her pair of sex chromosomes to Baby. Which one? She can give Baby the long one or the short one. Poppa bird has two long X chromosomes. So whichever one Poppa gives, it will be long. If Momma also gives an X chromosome, Baby will have two long ones. Gee... that would make him a boy. If Momma gives the short chromosome, then Baby will have one long and one short, so she'll be a girl.

Ok, so the baby girls always get their X chromosome (the long one), from Poppa. Well, the information about lutino, opaline, and cinnamon is on that X chromosome. If a baby girl bird is (or isn't) lutino, opaline, or cinnamon, it's because of the X chromosome her poppa gave her. Does it matter if the momma is lutino? Not to the daughters. Or opaline, or cinnamon? Not to the daughters.

Well, lets suppose Poppa has one lutino gene. His genes on the X chromosomes would have the following disagreement:

Poppa would look green.

Now suppose it's breeding time and Poppa is giving out his X chromosomes to his kids. Sometime babies will receive a lutino gene and some won't. Then Momma gives them another X chromosome and they become boys, or she gives them a little short chromosome and they become girls. (Hey, can we call that little short chromosome a "y" chromosome? It's quicker than always having to type "little short chromosome").

If Momma is green, that means the gene on her X chromosome is like this:

So she gives her sons the X chromosome and they get either a lutino gene or no lutino gene from Poppa:

Momma gives her daughters the y chromosome and they get either a lutino gene or no lutino gene from Poppa:

So we just showed that a green Momma and a green Poppa can have a lutino baby girl, but not a lutino baby boy. This can happen when the green Poppa is split to lutino.

Remember that in budgies, the cinnamon and opaline genes behave exactly the same way as the lutino gene:

Cinnamon daughters only get a cinnamon gene from their dads.
Two non-cinnamon parents can still create a cinnamon daughter if the dad has one cinnamon gene.

Opaline daughters only get an opaline gene from their dads.
Two non-opaline parents can still create an opaline daughter if the dad has one opaline gene.

Yes! I want more no-tech genetics!


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