Molecular Genetics

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The concept of the genetic chromosome evolved from studies of the behavior of genetic markers during the propagation of organisms.

The genetic chromosome is represented by a genetic map.

• Genetic maps are unbranched lines or circles with marks indicating the relative positions of genetic markers.
• Genetic markers are genetically determined traits or characters that are polymorphic in the population being studied. Polymorphic means that at least two forms of the trait occur in the population.
• If two markers are genetically linked, they are on the same genetic map, also called a linkage map. The set of all markers on the same linkage map is called a linkage group.
• If two markers are not genetically linked they are said to be unlinked markers and belong to different linkage groups.
• Phenotypic markers can be assigned to locations on molecularly marked genetic chromosomes.

Chromosomes can also be thought of as morphological entities or as DNA molecules.