Marker assisted selection (MAS) in racing pigeons

Genetics explained simply:

Imagine each pigeon carrying a unique cookbook. This cookbook contains chapters we call chromosomes . Each chapter contains specific recipes called genes . Each recipe consists of special letters called nucleotides : adenine (A), thymine (T), cytosine (C) and guanine (G). These nucleotides form the basis of the DNA and are the basic ingredients of every recipe in the cookbook. These recipes determine everything about the pigeon: the colour of its feathers, the colour of its eyes, its physique, and so on.

There are always different variations of the same recipe: there are blue pigeons, white pigeons, scalloped pigeons, black pigeons, etc. These variations in the gene for feather colour are called alleles. In pigeons, for example, there may be one allele that causes white feathers and another allele that causes blue feathers. The specific pair of alleles that a pigeon has for a particular gene, for example for feather colour, is called the genotype of that pigeon. So the genotype is the exact version of the recipe in the pigeon cookbook. But the actual characteristics of the pigeon, such as the colour of its feathers, are called the phenotype . This depends, among other things, on the combination of alleles and gene expression. So, while the genotype describes the instructions in the recipe, the phenotype is the actual cake baked according to the recipe. 

An example:

Most pigeons in the wild have the LDHA(GG) genotype. We call this common, typical recipe for the LDHA gene the wild type. The other allele occurring at this locus, LDHA(A), can be considered a variation or mutation of the wild type. Whether this mutation affects the pigeon should always be carefully investigated.

The influence of lineage:

Pigeons, like humans, have 2 copies of each chromosome (or chapter in the cookbook). That means they have two alleles of each gene, which forms their genotype. This double set of chromosomes makes the pigeon diploid. When pigeons reproduce and lay eggs, they pass on only half of their chromosomes to their young. This means that for each chapter in the cookbook, the youngster gets 1 chromosome from the father and 1 chromosome from the mother. So the young will get a mix of genes (or recipes) from both parents. Depending on the mix of alleles it gets, it will have its own unique genotype, and this genotype will eventually influence the phenotype of the young.