As breeders of utility poultry we are interested in the factors which affect features such as : egg colour; egg numbers; meat production; viability; start of lay; length of lay; sexing chicks

I hope through this site - from information sent in and articles / books we can all find we can create a pool of knowledge to help us all restore our pure breeds to the best of our ability.

In many organisms, sex of the individual is determined genetically by the presence or absence of particular sex-chromosomes. For example: in humans, XX is female, XY is male; in chickens, ZW is female, ZZ is male (ie the male is homogametic not the female).

Definitions:
autosomal trait :- a gene carried on a non-sex chromosome and present in two copies in both sexes.
sex-linked trait - a gene carried on the sex chromosome that is present in both sexes; one copy in one sex, two in the other. In mammals, this is the X chromosome (one copy in males, two in females).
In birds, this is the Z chromosome (one copy in females, two in males).

Interactions among genes
While one gene may make only one protein, the effects of those proteins usually interact. Novel phenotypes often result from the interactions of two genes, as in the case of the comb in chickens. The single comb is produced only by the rrpp genotype. Rose comb (b) results from R_pp. (_ can be either R or r). Pea comb (c) results from rrP_. Walnut comb, a novel phenotype, is produced when the genotype has at least one dominant of each gene (R_P_).

Pleiotropy is the effect of a single gene on more than one characteristic. An example is the "frizzle-trait" in chickens. The primary result of this gene is the production of defective feathers. Secondary results are both good and bad; good include increased adaptation to warm temperatures, bad include increased metabolic rate, decreased egg-laying, changes in heart, kidney and spleen.

Purebred stocks:
Linkage complicates the calculations but can be accommodated by the arithmetic method. Consider this simple example in chickens (for example :Araucanas). The dominant mutant controlling pea comb (P) and that controlling blue egg shell (O, the presence of oöporphyrin) are approximately five crossover units apart on an autosome (Bitgood 1985). The dominant mutant rose comb (R) is independent of the other two. What fraction of the female offspring would be normal from the mating of a parent heterozygous for P, O, and R and a parent heterozygous only for R?

The probability of getting the wild-type allele at the P locus is 1/2, and the probability of getting it with the wild-type allele for the O locus by crossover is 1/20. The probability of getting the wild-type allele at the R locus from both parents is 1/4. The product of these probabilities is the answer, 1/160.

LETHAL GENES
- some combinations of alleles produce lethal combination
In Chickens this trait is called creeper - shortened legs in heterozygous condition and is shown in the (scots dumpy)
Cross of 2 long legged (homozygous) chickens ---> all offspring live and are long legged
Creeper x creeper : 1/3 normal, 2/3 creeper
1:2 ratio - like 1:2:1 except that last one is missing as the homozygous creeper gene results in chicks dying in the shell or just after hatching

So the short legged Creeper bird is heterozygous Cc
Cc x Cc
1/4 CC normal
1/2 Cc: creeper
1/4 cc :lethal before birth
This is a lethal recessive – only fatal in homozygous condition

Chicken genetics

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