The genetics of comb type of chickens is historically significant. GENETICS OF COMB TYPEĬhickens have a variety of comb types, as shown in Figure 2.
#Silkie chicken blue skin
These traits include comb type, feather color, shank/foot color, and skin color. When breeding chickens, it is helpful to understand why certain significant observable traits exist in certain chickens. GENETICS OF SIGNIFICANT OBSERVABLE TRAITS IN CHICKENS The result is the range of brown color observed in eggs laid by different breeds of chickens. Brown shell color in eggs, for example, is controlled by as many as 13 genes. Such traits are called quantitative traits. A particular trait can be controlled by numerous gene pairs. To confuse things further, not every trait is controlled by a single pair of genes. The contribution from each gene in the pair can be equal, or the contribution can be dominated more by one gene than the other. This phenomenon is referred to as codominance. In some gene pairs, however, each gene is capable of some degree of expression in the heterozygous condition. Typically, in the heterozygous condition, the dominant gene is expressed over the recessive gene. (The two variant forms of the gene in such a gene pair are called alleles.) The heterozygous condition occurs when one gene present is the dominant gene and the other is the recessive gene. The homozygous recessive condition occurs when both genes present are the recessive gene. When dealing with a trait for which there is a dominant gene and a recessive gene, three conditions (combinations of the genes in the gene pair) can occur. The homozygous dominant condition occurs when both genes present are the dominant gene. A gene that can express itself only in the homozygous state is referred to as a recessive factor. A gene that can express itself in the homozygous state or the heterozygous state is referred to as a dominant factor. If the genes are different, the genetic state is referred to as heterozygous. If the genes are the same, the genetic state is referred to as homozygous. The phenotype for a specific trait in a chicken depends on the makeup of the gene pair for that trait. Each parent contributes one gene in each pair of genes. Jacquie Jacob, University of Kentucky).īecause chromosomes come in pairs, genes also come in pairs. Sex chromosomes of mammals and birds (Image created by Dr. Autosomes are all the chromosomes except the sex chromosomes.įigure 1.
The sex chromosomes of mammals and birds are illustrated in Figure 1. In chickens, the sex chromosomes are referred to as Z and W. A chicken having the sex chromosomes ZW is female, and a chicken having the sex chromosomes ZZ is male. A human having the sex chromosomes XX is female, and a human having the sex chromosomes XY is male. In humans, the sex chromosomes are referred to as X and Y. The sex chromosomes carry the genetic material that determines the sex of an offspring. The two categories of chromosomes are sex chromosomes and autosomes. Examples of aspects of a chicken’s phenotype include body shape, feather color, eye color, comb type, and so on. Phenotype-The observable physical or biochemical characteristics of an organism resulting from its genotype.Genotype-The genetic makeup of an organism.Chromosomes typically come in pairs, with one set donated from the mother and one from the father. Chromosomes function in the transmission of hereditary material from one generation to the next. Chromosome-A structure containing a complete strand of DNA.Gene-A segment of DNA that carries a blueprint for the function of a cell and, ultimately, a particular characteristic of an organism.DNA is arranged in the double helix–shaped strands. DNA (short for deoxyribonucleic acid)-The material containing the genetic instructions used in the development and function of an organism.In particular, it is useful to understand the key elements of genetics and to know why certain traits exist in certain chickens.Ī basic knowledge of poultry genetics begins with understanding the following key terms: If you breed poultry or are considering breeding poultry, a basic knowledge of poultry genetics is important.
0 kommentar(er)
