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Genetics is a hugely complicated subject, often made more so by the fact that it is rarely black or white, there are hundreds of shades of Gray or dominance in the middle. The well tried and tested rule that most casual chickens breeders seem to adhere to is “Like Begets Like”. They lump four hens and a cockerel and a cockerel into a breeding pen with little thought of what they are actually doing. Specimens that lack long and careful pedigree won’t give you decent results in the long run.
What determines the colour of chickens? Glossary and definition of terms used with poultry breeding:Allele -An allele is a gene that is a member of a set of genes that all belong to the same locus, or location, on a chromosome. One of a number of possible alternative forms of genetic information at a gene locus . A member of a set of genes that all have the same location on a given chromosome. Epistasis – suppression of the effect of a gene by a non-allelic gene .
A gene for trait A somehow having an effect on trait B is an example of epistasis. A piece of DNA in a chromosome that contains the coded information for a trait. A gene is a piece of DNA that carries information about a specific trait. Gene : An inheritable characteristic attached to the chromosome. Heterosis – The deviation between the cross and mid parent means . The difference in some property, for example rate of lay, between a cross bred line and the average for the parent lines.
Autosomal: An autosome is any of the numbered chromosomes, as opposed to the sex chromosomes. In general, the gamete has only half the chromosomes of a mature individual. Mitosis: There are two types of cell division processes. In the metaphase spindle fibres emminate from the centrioles and attach to the chromosomes. In the telophase the cell wall closes and new cells are evident. The cells that initiate meiosis contain the full set of chromosomes. Which chromosomes of the original ones find their way to the gamete cells is essentially a random process.
Dam: The Dam is the female chicken although this term is normally used only when describing hens used in a breeding program. Sire: The male chicken in a breeding program. Chromosome: A vehicle for carrying the birds genetic make-up. Chickens, like people, usually have two of every chromosome. The chromosomes in a chromosome pair are not identical, since one comes from each parent.
The sex chromosomes are unique in that there are two types, a long sex chromosome, the Z chromosome, and a short sex chromosome, the W chromosome. The female has one long and one short sex chromosome, she has ZW sex chromosomes. The male has two long sex chromosomes, he has ZZ sex chromosomes. For this reason, the female has only one copy of some genes that are on the long, Z, sex chromosome. Both male and female chickens have two of these genes.
An important point is that, when we talk about adding or removing a gene, say frizzle, F, we don’t intend that the chromosome is lengthened or shortened by the addition or deletion of that gene. I used the frizzle gene as an example here, but the statement applies to all genes. The first generation of progeny from the parental cross is referred to as the first filial generation, F1. In certain breeds the standard decrees that the characteristics of the male and female should be different, which necessitates double-mating, explained below. Where the standard for the two sexes is practically the same, then single mating is sufficient.