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STEPWISE EVOLUTION. "Throughout mammalian evolution, recombination between the two sex chromosomes was suppressed in a stepwise manner. It is thought that the suppression of recombination led to an accumulation of deleterious mutations and frequent genomic rearrangements on the Y chromosome." https://lnkd.in/d5x7tBt View in LinkedIn

SPREAD BY CREEP. "Can recombination decrease without chromosome rearrangements, just by spread of recombination modifiers with small effects?" http://www.nature.com/hdy/journal/v95/n2/full/6800697a.html View in LinkedIn

GRADUAL OR DISCONTINUOUS. "Was recombination suppression in mammals a discontinuous process (due to successive inversions or translocations), or did it evolve gradually?" http://www.nature.com/hdy/journal/v95/n2/full/6800697a.html View in LinkedIn

NO CROSSOVER. "There is now evidence from several taxa (mammal, birds and plants) for more than a single event of cessation of recombination between X and Y chromosomes. The extent of DNA sequence divergence between homologous X/Y gene pairs of a single species has been found to vary greatly among genes, suggesting that different regions of the sex chromosomes have been nonrecombining for very different amounts of time, given that sequence divergence begins once crossing over between X and Y stops." http://www.nature.com/hdy/journal/v95/n2/full/6800697a.html View in LinkedIn

SINGLE LOCUS. "By this type of process, a single locus takes control of sex determination, that is, derived states with a single sex-determining gene can evolve. Single locus sex determination, such as that of mammals, with a single Y-linked gene, SRY, controlling sex, might also be able to evolve directly, but no detailed model has yet been worked out to show how this could occur." http://www.nature.com/hdy/journal/v95/n2/full/6800697a.html View in LinkedIn

NEW SEX GENES. "Another possible type of change is the emergence of a new sex-determining gene, epistatic to the previous sex determiner, so that the original genes no longer control sex development, as in the fly Musca domestica, and probably also in the medaka fish, Oryzias latipes. The sex-determining region of the fly, Megaselia scalaris, appears to transpose between chromosomes, creating new potential sex chromosomes." http://www.nature.com/hdy/journal/v95/n2/full/6800697a.html View in LinkedIn

GUT MICROBIOME EXAMPLE. “For instance, as recently reviewed, the role of the gut microflora community is becoming increasingly recognized as a key factor in the onset of inflammatory diseases.” https://lnkd.in/gEfVGaC View in LinkedIn

REDUCED EXPRESSION. "It is possible that a build-up of transposable elements on a proto-Y or neo-Y could reduce gene expression on these chromosomes, through chromatin modification due to dsRNA interference, which is known to be associated with the presence of transposable elements." http://www.nature.com/hdy/journal/v95/n2/full/6800697a.html View in LinkedIn

NEW PARADIGM NEEDED. “The transition to a broader pathobiome perspective involves revisiting the Koch and Hill's postulates at the level of microbial communities, and raises the question of the nature and diversity of the microbiota present in a healthy individual, and of factors promoting the emergence of potentially disease-causing pathobiomes.” https://lnkd.in/gEfVGaC View in LinkedIn

"GENETIC DEGENERATION may be partly driven by this accumulation, or may occur independently later on. In the D. miranda neo-Y, transposable elements appear to be inserted either into introns or intergenic sequences, and hence do not directly disrupt gene function (although one insertion causes downregulation of a gene." https://lnkd.in/gCh5RAX View in LinkedIn