Abstract
This second lecture dealt with the subject of biodiversity within species, i.e. phenotypic variation when the same genotype can lead to several phenotypes. The notion of diversity within a species might seem contrary to genetic determinism, but past studies have often ignored environmental and stochastic changes.
The example of chromosome inactivation X, a process that leads to cellular mosaicism in females, and the random monoallelic regulation of certain genes on autosomes, have been cited. In these cases, differential expression of one or other of the two alleles of a gene is triggered either by programmed or developmental signals, or stochastically, and then stably maintained by epigenetic mechanisms.
