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NO COMBINATION. "It is well understood that the idea that sex-determining genes should not recombine can explain the lack of recombination between X and Y chromosomes of animals such as Drosophila and mammals with male heterogamety (or Z and W in taxa with female heterogamety such as birds and Lepidoptera." https://lnkd.in/gCh5RAX View in LinkedIn

ANCIENT SILENCING MODULES. "These dosage systems cannot be identical by descent but were probably constructed from elements of ancient silencing mechanisms that are ubiquitous among vertebrates and shared throughout eukaryotes." https://lnkd.in/gWDQizV View in LinkedIn

SIMILAR MODULES. "Systems that compensate for different gene dosages include a wide range of global, regional and gene-by-gene processes that differ in their extent and their molecular mechanisms. However, many elements of these control systems are similar across distant phylogenetic divisions and show parallels to other gene silencing systems." https://lnkd.in/gWDQizV View in LinkedIn

DOSAGE. "Differentiated sex chromosomes in mammals and other vertebrates evolved independently but in strikingly similar ways. Vertebrates with differentiated sex chromosomes share the problems of the unequal expression of the genes borne on sex chromosomes, both between the sexes and with respect to autosomes. Dosage compensation of genes on sex chromosomes is surprisingly variable — and can even be absent — in different vertebrate groups." https://lnkd.in/gWDQizV View in LinkedIn

NON-RECOMBINING. "The Chlamydomonas mating-type locus and incompatibility locus regions of some fungi with systems with two incompatibility types include large nonrecombining genome regions that differ in size, gene content and representation of transposable elements. The heteromorphic sex chromosomes of bryophytes, which are primarily haploid, represent a similar situation, although it is not yet known whether these homologous chromosome pairs show genetic degeneration." http://www.nature.com/hdy/journal/v95/n2/full/6800697a.html View in LinkedIn

YOUNG CHROMOSOMES. "We review some recently published results on sex chromosomes in a diversity of species. We focus on several fish and some plants whose sex chromosomes appear to be 'young', as only parts of the chromosome are nonrecombining, while the rest is pseudoautosomal." http://www.nature.com/hdy/journal/v95/n2/full/6800697a.html View in LinkedIn

"THE SHELTERING of recessive or partly recessive Y-linked deleterious mutations from selection due to their permanent heterozygosity” occurs. http://www.nature.com/hdy/journal/v95/n2/full/6800697a.html View in LinkedIn

"THE EVOLUTION of a pair of chromosomes that differ in appearance between males and females (heteromorphic sex chromosomes) has occurred repeatedly across plants and animals. Recent work has shown that the male heterogametic (XY) and female heterogametic (ZW) sex chromosomes evolved independently from different pairs of homomorphic autosomes in the common ancestor of birds and mammals but also that X and Z chromosomes share many convergent molecular features." https://lnkd.in/gT_EcE7 View in LinkedIn

"LACK OF RECOMBINATION among most genes carried on Y or W chromosomes reduces the ability of selection to fix favourable mutations and to prevent the fixation of deleterious ones, due to Hill–Robertson interference among completely linked loci (hitch-hiking processes)." http://www.nature.com/hdy/journal/v95/n2/full/6800697a.html View in LinkedIn

PHYSICALLY DIFFERENT. "The X and Y (or Z and W) chromosomes are often morphologically distinguishable (heteromorphic), with the Y or W being largely heterochromatic and containing a high proportion of repetitive DNA." http://www.nature.com/hdy/journal/v95/n2/full/6800697a.html View in LinkedIn