GENETIC SELECTION

Genetic selection

Selection is the stage of a genetic algorithm in which individual genomes are chosen from a population for later breeding (using the crossover operator).

Genetic selection is the process by which certain traits become more prevalent in a species than other traits. The traits seen in an organism are due to the genes found on their chromosomes. The genes code for the traits that we are able to observe.

Genes have more than one version or allele. We inherit one allele for every gene from each of our parents as shown in Figure 1. Some alleles are seen more frequently in a population because there are factors that select these genes.

In natural selection, natural forces determine the traits seen in an organism. A variation or allele of a trait makes some individuals more suited to survive in the environment. Mating behavior that leads to a sexual preference for a trait is also natural selection.

Natural selection also occurs when a species has a preference for certain traits for sexual reasons. Male peafowl (peacocks) have elaborate tail feathers because female peacocks are attracted to really nice tails. This is called sexual selection since traits are being selected for sexual reasons.


















Artificial selection involves human interference. Humans have been selecting various traits in other organisms for thousands of years. It is how we have developed a huge variety in the colors and flavors of apples. It is also the reason we have little tiny dogs and extremely large dogs. We select traits in plants and animals to use them to our advantage. Artificial selection in plants and animals is not seen as being as controversial, as it is with humans. Genetic selection in humans raises ethical questions, such as who gets Syndrome, Sickle Cell Anemia, Cystic Fibrosis, and Tay-Sachs disease, especially in cases where the mother is at risk.


Mass selection
Mass selection is a common plant breeding practice and effective when traits are highly heritable and easily identified.

Genotypic selection
Genotypic selection' is a term that refers to the. DNA-based enrichment of a particular allele.




Family selection
Family selection refers to mating of organisms from the same ancestral stock that are not directly related to each other. Pure-line selectioninvolves selecting and breeding progeny from superior.

Sib selection
Sib selection is a method of sequential fractionation of a heterogeneous sample that can be applied to isolation of a sequence, gene, or gene family from a complete library.

Progeny testing
Progeny testing is a process by which a sire's genetic merit is measured through the performance of his progeny. Progeny testing is relevant in sheep when meat yield and meat quality traits are important selection criteria.

Combined selection
Combined selection is a technique used to identify individuals with better additive genetic value in a population under selection, using information from the individual itself and its relatives. Such procedure should increase the efficiency of the selection process, maximizing the expected genetic gain. This selection procedure was discussed first by Lush (1947a,b) and can be used successfully in both animal and plant breeding (Bueno Filho, 1992 and Morais, 1992). Its main limitation may be a marked reduction in the genetic variability in the population, with one or few selection cycles, because of the great decrease in its effective size resulting from the selection of many related individuals (Morais, 1992). However, this can be overcome by defining a maximum number of individuals to be selected in the same family (Morais, 1992).