Biology as Poetry: Genetics

Bacteriophage Ecology Group

Genomic Equivalence

The consistency of the DNA content of most of the cells found within multicellular organisms despite the often profound differentiation of the cells making up these organisms.

Genomic equivalence is simply shorthand for the idea that cells can change phenotypically without also changing genotypically. There are exceptions, however.

For example, some genotypic change does occur in the course of maturation of the B cell and T cells that underlie adaptive immunity in vertebrate animals. In addition, liver cells of mammals can be polyploid while erythrocytes (red blood cells) along with platelets are cell-like forms (formed elements) that lack genotype altogether.

The greatest exception of all, though one that technically is not an exception, are the products of meisosis, i.e., eggs, sperm, spores, and zoospores. These cells are both all haploid (versus diploid for somatic as well as germline cells) and have been subject to genetic recombination, thus "scrambling" the DNA that had been found in their parental cells.

These cells, however, literally represent new individuals, i.e., the next generation, and therefore, technically, are not expected to display genomic equivalence with the parental organism that produced them.

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