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TWISTS AND TURNS. "Some species have newly gained or secondarily lost their sex chromosomes; in others, a different chromosome has replaced the original sex chromosome or multiple chromosomal elements have become incorporated into the sex chromosomes; still other species have female heterogametic sex chromosomes." https://lnkd.in/dX2rADH View in LinkedIn

PARALLEL EVOLUTION. "Transcriptome analysis shows that dosage compensation has evolved multiple times in flies, consistently through up-regulation of the single X in males. However, X chromosomes generally show a deficiency of genes with male-biased expression, possibly reflecting sex-specific selective pressures." https://lnkd.in/dX2rADH View in LinkedIn

HIDDEN DIVERSITY. "Here, we use whole-genome analysis in 37 fly species belonging to 22 different families of Diptera and uncover tremendous hidden diversity in sex chromosome karyotypes among flies. We identify over a dozen different sex chromosome configurations, and the small dot chromosome is repeatedly used as the sex chromosome, which presumably reflects the ancestral karyotype of higher Diptera." https://lnkd.in/dX2rADH View in LinkedIn

GREAT VARIATION. "Sex is a universal feature of eukaryotic organisms, yet tremendous variation in sex determination mechanisms exists even among closely related species, or among individuals within a species." https://lnkd.in/dX2rADH View in LinkedIn

DEAD-END. "Highly differentiated sex chromosomes—a degenerate, gene-poor Y chromosome, and an often dosage-compensated X—appear to represent an evolutionary dead-end." https://lnkd.in/dX2rADH View in LinkedIn

"FUSIONS between sex chromosomes and autosomes are relatively easy to detect from karyotypic data, and a large number of such fusions have been discovered." https://lnkd.in/g2CPWtY View in LinkedIn

"AN AUTOSOME is a chromosome that is not an allosome (a sex chromosome). Autosomes appear in pairs whose members have the same form but differ from other pairs in a diploid cell, whereas members of an allosome pair may differ from one another and thereby determine sex." https://lnkd.in/gP9J5mi View in LinkedIn

BOTH SYSTEMS AT ONCE. "In some taxa, such as fishes and squamate reptiles, both XY and ZW sex determination is found among closely related species (and even among populations within a species)." https://lnkd.in/g2CPWtY View in LinkedIn

STEPPED STRATA. "Such a recombination restriction occurred in a stepwise manner along most of the sex chromosomes in parallel in birds and mammals (creating so-called “evolutionary strata”), apart from small pseudoautosomal regions (PARs) that maintain recombination." https://lnkd.in/gxyp7ei View in LinkedIn

TWO SYSTEMS. "Genetic sex-determining systems in vertebrates include two basic types of heterogamety, which are represented by the XX/XY and ZZ/ZW types. Both types occur among amphibian species." https://lnkd.in/gFCg7HY View in LinkedIn