In 1922 R. A. Fisher introduced the method of maximum likelihood. He first presented the numerical procedure in 1912. This paper considers Fisher's changing justifications for the method, the Ž concepts he developed around it including likelihood, sufficiency, effi-. Ž ciency and information and the approaches he discarded including . inverse probability .

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Ribosomal RNA gene (rDNA) copy number variation modulates heterochromatin formation and influences the expression of a large fraction of the Drosophila ge-nome. This discovery, along with the link between rDNA, aging, and disease, high-lights the importance of understanding how natural rDNA copy number variation arises. Pursuing the relationship between rDNA expression and stability, we have discovered that increased dietary yeast concentration, emulating periods of dietary excess during life, results in somatic rDNA instability and copy number reduction. Modulation of Insulin/TOR signaling produces similar results, indicating a role for known nutrient sensing signaling pathways in this process. Furthermore, adults fed elevated dietary yeast concentrations produce offspring with fewer rDNA copies demonstrating that these effects also occur in the germline, and are transgenera-tionally heritable. This finding explains one source of natural rDNA copy number variation revealing a clear long-term consequence of diet.

Intragenomic conflict describes a phenomenon in which genetic elements act ‘selfishly’ to gain a transmission advantage at the expense of the whole genome. A non-essential, selfish B chromosome known as Paternal Sex Ratio (PSR) induces complete elimination of the sperm-derived hereditary material in the jewel wasp Nasonia vitripennis. PSR prevents the paternal chromatin from forming chromosomes during the first embryonic mitosis, leading to its loss. Although paternally transmitted, PSR evades self-elimination in order to be inherited. We examined important post-translational modifications to the DNA packaging histones on the normal genome and the PSR chromosome in the fertilized embryo. Three histone marks – H3K9me2,3, H3K27me1, and H4K20me1 – became abnormally enriched and spread to ectopic positions on the sperm’s chromatin before entry into mitosis. In contrast, other histone marks and DNA methylation were not affected by PSR, suggesting that its effect on the paternal genome is specific to a subset of histone marks. Contrary to the paternally derived genome, the PSR chromosome was visibly devoid of the H3K27me1 and H4K20me1 marks. These findings strongly suggest that PSR causes paternal genome elimination by disrupting at least three histone marks following fertilization, while PSR avoids self-elimination by evading two of these marks.