Why not Y naught

Heat shock factor 5 establishes the male germ-line meiotic sex chromosome inactivation through regulation of Smarca4

“…At the early pachytene stage of the male mammals, homologous autosomes are fully synapsed [ 3 ]. But the X and Y chromosomes synapse only at a region of limited sequence homology [ 4 ]. Therefore, the remaining asynapsed X and Y chromosome need to undergo meiotic sex chromosome inactivation (MSCI) to cross the pachytene checkpoint and maintain the normal development of germ cells [ 5 ].…”

Comprehending the dynamism of B chromosomes in their journey towards becoming unselfish

“…In animals, Bs imparting adaptive significance have been reported in the frog Leiopelma hochstetteri ( Yoshida et al, 2011 ), moths Tischeria ekebladella ( Dalíková et al, 2017 ), Plutella xylostella ( Dalíková et al, 2017 ), Iulia ohridella ( Dalíková et al, 2017 ), and iulia butterfly Dryas iulia ( Lewis et al, 2021 ), passerie birds ( Kinsella et al, 2019 ; Torgasheva et al, 2019 ) and fish A. mexicanus ( Imarazene et al, 2021 ). It is interesting to note that Bs might behave as sex chromosomes themselves as described in cichlid fish and are also proposed to participate in sex determination ( Camacho, 2005 ; Clark and Kocher, 2019 ; Jonika et al, 2022 ). Sex chromosome system lability is a well-known phenomenon, and the possibility of losing an existing sex chromosome and incorporation of new genomic regions and/or involvement of B chromosomes is suggested as a possible canonical origin of sex chromosomes ( Jonika et al, 2022 ).…”

“…It is interesting to note that Bs might behave as sex chromosomes themselves as described in cichlid fish and are also proposed to participate in sex determination (Camacho, 2005;Clark and Kocher, 2019;Jonika et al, 2022). Sex chromosome system lability is a well-known phenomenon, and the possibility of losing an existing sex chromosome and incorporation of new genomic regions and/or involvement of B chromosomes is suggested as a possible canonical origin of sex chromosomes (Jonika et al, 2022). Bs and Y/W are gene-poor chromosomes and by mechanisms like transposition of ancestral Y-determiner from Y or emergence of a novel determiner (Pan et al, 2021), Bs can acquire a sex-determining factor.…”

“…In contrast to the above few reports, however, recent evidence showcases the advantages offered by Bs to the hosts, especially in species that do not possess a drive mechanism. This feature is considered as yet another evolutionary adaptation route taken by Bs to maintain their survival in diverse plant, fungal and animal species ( Müntzing, 1954 ; Jackson and Newmark, 1960 ; Moss, 1966 ; Williams, 1970 ; Dover and Riley, 1972 ; Dherawattana and Sadanaga, 1973 ; Rees and Hutchinson, 1974 ; Puertas et al, 1987 ; Staub, 1987 ; Holmes and Bougourd, 1989 ; Miao et al, 1991 ; Plowman and Bougourd, 1994 ; Enkerli et al, 1997 ; Burt and Trivers, 1998 ; Hatta et al, 2002 ; Nokkala et al, 2003 ; Rodriguez-Carres et al, 2008 ; Akagi et al, 2009 ; Coleman et al, 2009 ; Ma et al, 2010 ; Yoshida et al, 2011 ; Kousaka and Endo, 2012 ; Balesdent et al, 2013 ; Houben et al, 2014 ; Thatcher et al, 2016 ; Williams et al, 2016 ; Dalíková et al, 2017 ; Pereira et al, 2017 ; van Dam et al, 2017 ; Ruban et al, 2017 ; Armitage et al, 2018 ; Plaumann et al, 2018 ; Kinsella et al, 2019 ; Torgasheva et al, 2019 ; Ahmad et al, 2020 ; Dalla Benetta et al, 2020 ; Birchler and Yang, 2021 ; Imarazene et al, 2021 ; Lewis et al, 2021 ; Pokorná and Reifova, 2021 ; Boudichevskaia et al, 2022 ; Camacho, 2022 ; Chen et al, 2022 ; Jonika et al, 2022 ; Komluski et al, 2022 ; Shi et al, 2022 ).…”

“…Evidence has also been put forth to suggest the origin of the Y chromosome from the Bs in fruit fly D. melanogaster , insect Cacopsylla peregrina, and cichlid fish of the tribe Oreochromini ( Conte et al, 2021 ; Jonika et al, 2022 ). Y is a genic poor chromosome and none of the Y-linked genes find a homolog on X, and since all the identified paralogs lie on autosomes it was proposed that the Y chromosome might be B-derived in the fruit fly ( Carvalho, 2002 ) or may be a product of fusion of ancestral Y with an autosome ( Bachtrog, 2013 ).…”