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genetic resources for (budgerigar) breeders
Genes & Traits
A gene is a piece of a DNA molecule. It has a start and an end and it contains the codes for a specific protein. A protein in its basic form is a sequence of amino acids. Three bases of DNA code for one amino acid. The three bases are called a codon. So the DNA of the gene codes for a sequence of amino acids in a protein.
These proteins are really the work horses of a cell: they do all the work. Some proteins are catalysts for biochemical reactions like converting sugar into energy. Other proteins act as gateways on the cell membrane to allow nutrients in. Some are building blocks for other structurs like for instance feathers.
Since proteins do all the work they are responsible for most traits. Take for instance a protein that helps in the production of the yellow pigmentation in the feathers. Suppose this protein suddenly wasn't produced anymore? Then the feather won't have yellow pigments. In case of budgerigars you would get a skyblue in stead of a lightgreen.
Genes, Proteins & Traits
Imagine a base pair gets changed in a gene. It will then code for a different protein. Sometimes these difference don't influence the workings of the protein but quite often they do. Suppose this was the gene coding for the proteins involved in the production of the yellow pigmentation. You already guessed it: a skyblue bird.
More genes and more traits
Please note that mostly multiple genes are involve in a trait. Take for instance size. You will understand that not just one gene will influence this. But also 'simple' traits like eye colour are almost always determined by different genes.
On the other hand, one gene can also influence multiple traits.
On a final note: also environmental influences can influence traits. Imagine the influence of malnutrition on size.