heterozygous

A little history

As we know today, Gregor Mendel, best known for his experiments with peas, was the basis of genetics. He demonstrated through his experiments that if he crossed two peas (F1) with different characteristics such as flower color, leaf size ... Then the offspring (F2) kept the characteristics of a single parent. All the flowers of these young peas had the same color and size of leaves.
It’s as if they “lost” one of the properties. When he crossed these young F2 peas with each other, the F1 characteristics reappeared among the offspring of the F3 generation. Mendel called these characteristics shown by F2: Dominant. And the characteristics hidden in the F2 have been called recessive.

Currently we still call it dominant and recessive. However we do know that Mendel discovered "complete dominance". There are indeed other forms of dominance. We already know these forms so we will mainly bring a few provisions to remember.

Some concepts

We know that genes carry characteristics and that these genes are located on chromosomes. There are genes that deal with the color of the eyes, the color of the legs, the size of the beak… Chromosomes are found in the cells of the body: They are stored in the nucleus of each cell. In each nucleus of each cell are the genes for the color of the eyes, the color of the legs, the size of the beak ... However, the functioning of the “color of the eyes” genes is manifested only in the eyes. In the paws, the "eye color" genes do not show up. Each cell therefore “knows” where it is located in the body and which genes it must activate.
Chromosomes go in pairs, all genes are found in pairs. So for the eye color gene, we have two genes. This also applies to the color of the legs, the size of the beak ... These two genes for the color of the eyes can cause a color of the eyes blue. It is also possible that one gene is responsible for the color blue and the other for the color brown. (which does not mean that the being will have one blue eye and the other brown, the brown of the eyes is dominant over the blue, so both eyes will be brown).

1. Introduction

The breeding and competition of zebrafinch has grown considerably over the past fifteen years. In order to improve the size of the new mutations, breeders also have recourse to conventional "split" birds.
Some manage to combine several mutations. All this made it essential to know a minimum of applied genetics. It is this minimum that I would like to present to novice breeders.
This is not a complete course in genetics, but a simple presentation of the method I use preceded by some basics.

2. The zebrafinch and its mutations

A zebrafinch has a number of visible characters (size, shape, designs, color, sex) that constitute its phenotype. It can have, in addition to other unexpressed traits (it is said to be a split). The set of traits, expressed or not, is called the genotype.

A young zebrafinch grows out of an egg cell, the result of the fusion of the nucleus of a father's sperm and the nucleus of the female's egg. The bird's genetic program is already there: A series of cell divisions and coded information will (or not) trigger the appearance of the characters. The encoded information is carried by genes located on long filaments contained in the nucleus: chromosomes.
All chromosomes go in pairs: each chromosome therefore has its counterpart.

There are two categories of chromosomes :

- Sex chromosomes :
• XX in the male
• XY in the female

- Autosome chromosomes.

The gray zebrafinch living in Australia is the source of all of our farmed zebra finches. It has a whole set of genes distributed in its chromosomes.Whenever a new mutation has appeared, there has been a change in an original gene (and it has been shown to be hereditary). The original gene and the mutated gene are located in the same place called a locus on each of the homologous chromosomes.
Both genes are alleles.



A bird is pure (homozygous) when all of its alleles carry identical information.
A bird is heterozygous when at least one pair of alleles carries different information about the same trait.

We currently know about twenty different mutations of the gray zebrafinch.