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SIGNIFICANCE: Parthenogenesis is unisexual reproduction through the development of unfertilized eggs, which produces offspring that are genetically alike. This clonal reproduction strategy is used by a number of species, especially for rapid reproduction under favorable conditions, and it appears to offer a selective advantage to creatures living in disturbed habitats.

SIGNIFICANCE: In sexual reproduction, parents produce specialized cells (eggs and sperm) that fuse to produce a new individual. Each of these cells contains one copy of each of the required units of information, or genes, which provide the blueprint necessary for the offspring to develop into individual, functioning organisms. Transmission genetics refers to the passing of the information needed for the proper function of an organism from parents to their offspring as a result of reproduction.

The development of the microscope made it possible to study what became recognized as the central unit of living organisms, the cell. One of the most obvious structures within the cell is the nucleus. As study continued, dyes were used to stain cell structures to make them more visible. It became possible to see colored structures called chromosomes (“color bodies”) within the nucleus that became visible when they condensed as the cell prepared to divide.

SIGNIFICANCE: Complete dominance represents one of the classic Mendelian forms of inheritance. In an individual that is heterozygous for a trait, the allele that displays complete dominance will determine the phenotype of the individual. Knowing whether the pattern of expression of a trait is dominant or recessive helps in making predictions concerning the inheritance of a particular genetic condition or disorder in a family’s history.