Month: September 2022

FIRST AND SECOND MAJOR UPHEAVAL. "The first corresponded to the divergence of monotreme mammals (platypus and echidna) from the rest, and the second to the divergence of marsupials from placental mammals (including humans)." https://lnkd.in/ehjz378 View in LinkedIn

BRANCH IN THE TREE. "I propose that drastic sex chromosome changes could have played a direct role in separating our lineage (placental mammals), first from the egg-laying monotremes, then from marsupials." https://lnkd.in/ehjz378 View in LinkedIn

STRANGE EVOLUTION. "Sex chromosomes are really weird because of the way they evolved. They start off as ordinary chromosomes, known as autosomes. A new sex gene arises on one member of the pair, defining either a male-determining Y as in humans or a female-determining W as in birds." https://lnkd.in/ehjz378 View in LinkedIn

Civil servants bordering on clueless over Brexit. A brilliant piece of writing. View in LinkedIn

GENE DEGRADATION. "The acquisition of a sex factor on one member of the pair is the kiss of death for that chromosome, and it degrades quickly. This explains why only a few active genes remain on the human Y and the bird W." https://lnkd.in/ehjz378 View in LinkedIn

SUCCESSION RISKS. "When old sex chromosomes self-destruct, a new sex gene and sex chromosomes may take over. This is fraught with peril because the interaction of old and new systems of sex determination is likely to cause severe infertility in hybrids." https://lnkd.in/ehjz378 View in LinkedIn

SEX WARS. "Rival sex genes may be at war with each other, causing intersexual development, or at least infertility. For instance, what will be the sex of a hybrid that has both a male-determining Y and a female-determining W?" https://lnkd.in/ehjz378 View in LinkedIn

GENE SHORTAGE AND COMPENSATION. "Added to this are problems with gene dosage because the degenerate Y and the W have few genes. If an XY male mates with a ZW female, most of the progeny will be short of genes. There may also be problems with gene dosage because genes on the X and the Z are used to working harder to compensate for their single dosage." https://lnkd.in/ehjz378 View in LinkedIn

DEFINING EVENT. "Sex chromosome change has occurred very rarely in mammals, so it seems significant that each change corresponds to a major divergence. That's why I propose that sex chromosome turnover separated monotremes from the rest of the mammals, and sex chromosome fusion occurred later to separate our lineage from marsupials." https://lnkd.in/ehjz378 View in LinkedIn

SPECIATION. "Strengthening the argument that sex chromosome turnover begets speciation is evidence of a new round of sex chromosome change and speciation." https://lnkd.in/ehjz378 View in LinkedIn