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).

Practical Manual B.Voc

Fresh water fishes
Catla catla










1. Catla (Catla catla), also known as the major (Indian) carp.
2. Catla is a fish with large and broad head, a large protruding lower jaw and upturned mouth. It has large, greyish scales on dorsal side and whitish on belly.
3. Body short and deep, somewhat laterally compressed, its depth more than head length;
4. head very large, its depth exceeding half the head length;
5. body with conspicuously large cycloid scales,


Kingdom: Animalia

Phylum: Chordata

Class: Actinopterygii

Order: Cypriniformes

Family: Cyprinidae

Genus: Labeo

Species: L. rohita

Labeo rohita






1. Body bilaterally symmetrical, moderately elongate, its dorsal profile more arched than the ventral profile;
2. Body with cycloid scales, head without scale; snout fairly depressed, projecting beyond mouth, without lateral lobe; eyes dorsolateral in position, not visible from outside of head;
3. Mouth small and inferior; lips thick and fringed with a distinct inner fold to each lip, lobate or entire;
4. A pair of small maxillary barbels concealed in lateral groove; no teeth on jaws; pharyngeal teeth in three rows; upper jaw not extending to front edge of eye;
5. Simple (unbranched) dorsal fin rays three or four, branched dorsal fin rays 12 to 14; dorsal fin inserted midway between snout tip and base of caudal fin;
6. Pectoral and pelvic fins laterally inserted; pectoral fin devoid of an osseous spine; caudal fin deeply forked
7. Colour bluish on back, silvery on flanks and belly.













Kingdom: Animalia

Phylum: Chordata

Class: Actinopterygii

Order: Cypriniformes

Family: Cyprinidae

Subfamily: Labeoninae

Genus: Cirrhinus
Cirrhinus mrigala

1. Body bilaterally symmetrical and streamlined, its depth about equal to length
2. of head; body with cycloid scales,
3. Head without scales; snout blunt, often with pores; mouth broad, transverse; upper lip entire and not continuous with lower lip, lower lip most indistinct;
4. Single pair of short rostral barbels; pharyngeal teeth in three rows, 5.4.2/2.4.5 pattern; lower jaw with a small post-symphysial knob or tubercle;
5. Origin of dorsal fin nearer to end of snout than base of caudal; dorsal fin as high as body with 12 or 13 branched rays;
6. Unbranched ray of dorsal fin non-osseous and non-serrated; pectoral fins shorter than head; caudal fin deeply forked; anal fin not extending to caudal fin; lateral line with 40-45 scales;
7. Lateral transverse scale rows 6-7/5½-6 between lateral line and pelvic fin base; usually dark grey above, silvery beneath; dorsal fin greyish; pectoral, pelvic and anal fins orange-tipped