|
|
|
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
|
Fig. 3. Meiotic sterility caused by MSUC and by MSCI failure. (A) In
normal (XY) males, silencing of the single X chromosome by MSCI is tolerated
because essential X-encoded genes have autosomally integrated retrogene copies
that are expressed during the precise time-window of MSCI-to-PSCR. (B)
When autosomes fail to synapse, they are also silenced by MSUC. If unsynapsed
autosomal segments contain a gene or genes crucial for meiosis, those genes
will be silenced, causing meiotic arrest. (C) Allowing either the X or
Y chromosome to synapse, as seen in XYY males, allows MSCI escape, with the
ensuing expression of sex-linked genes causing meiotic arrest. (D) In
XX females, all chromosomes have homologues and are thus completely synapsed.
(E) In the XO female mouse, the single X chromosome has no synaptic
partner and is therefore silenced by MSUC. Because no autosomal retrogenes are
activated in the female gonad, these XO oocytes perish. (F) In
approximately one-third of XO oocytes, the single X chromosome circumvents
MSUC by synapsing non-homologously either with itself, to form a hairpin, or
with other chromosomes.
|
