Sex linked usually refers to a gene that is carried on the X or Y chromosomes - the so called sex chromosomes. In humans, males have an X and a Y gene, females have two X genes. In BUDGIES, its the other way around. Females are XY and males are XX.
Without going into great detail, the Y gene is basically non-functional when we talk about genetic traits. So sex linked genes are carried on the X gene. A new baby ALWAYS gets an X chromosome from the father (could be any one of his two X chromosomes). If it gets another X from its mother, it will be a boy. If it gets a Y chromosome, it will be a girl.
Thats why for a female to display a sex linked gene, it only needs one X chromosome carrying the gene - since it only HAS one X chromosome. So if a father is an albino which is sex linked - lets call it XaXa (to represent albino), and the mother is NORMAL (lets say XnY) then we can work out the odds of a particular baby getting the genes and who might DISPLAY it. Below is a rough punnet square showing mum and dads genes, and all possible variations for the kids.
Mom --- Xn / Y
Dad - Xa XaXn XaY
----- Xa XaXn XaY
As you can see, all the BOYS will be XaXn - meaning they are normal appearing birds (Xn) SPLIT for albino (Xa). ALL the females are XaY - they are visual albinos.
Hope this makes sense for a basic intro to sex linkage!
Does sex-linked mean? Is it that only the male carries the gene? Even if the female shows the gene she doesn't carry it?
Just in case you find Xs & Ys confusing I'll try to explain without them.
The male can carry a sex linked gene either in a visual form or in a split form. A female can only carry it in a visual form.
If a sex-linked male is mated to a normal female his daughters will all be visually the sex-linked mutation and his sons will all only carry the gene as split.
If a sex-linked female is mated to a normal male all the male chicks will carry the gene as split but the females won't have the gene in any form
If a normal male that is split for the mutation is mated to a female that is the mutation visually about half of the chicks of both sexes will be the mutation visually, the other half of the male chicks will carry the mutation as split and the second half of the females will not have the mutation in any form