Inactivation or non-reactivation: what accounts better for the silence of sex chromosomes during mammalian male meiosis?

Summary/AbstractRecombination suppression between sex chromosomes is often stated to evolve in response to polymorphisms for mutations that affect fitness of males and females in opposite directions (sexually antagonistic, or SA, mutations), but direct empirical support is lacking. The sex chromosomes of the fish Poecilia reticulata (the guppy) carry SA polymorphisms, making them excellent for testing this hypothesis for the evolution of sex linkage. We resequenced genomes of male and female guppies and, unexpectedly, found that variants on the sex chromosome indicate no extensive region with fully sex-linked genotypes, though many variants show strong evidence for partial sex linkage. We present genetic mapping results that help understand the evolution of the guppy sex chromosome pair. We find very different distributions of crossing over in the two sexes, with recombination events in male meiosis detected only at the tips of the chromosomes. The guppy may exemplify a route for sex chromosome evolution in which low recombination in males, likely evolved in a common ancestor, has facilitated the establishment of sexually antagonistic polymorphisms.

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Karyotype and male meiosis in Spartocera batatas and meiotic behaviour of multiple sex chromosomes in Coreidae (Heteroptera)

European Journal of Entomology ◽

10.14411/eje.2006.002 ◽

2006 ◽

Vol 103 (1) ◽

pp. 9-16 ◽

Cited By ~ 13

Author(s):

Maria Jose FRANCO ◽

Maria Jose BRESSA ◽

Alba GRACIELA PAPESCHI

Keyword(s):

Sex Chromosomes ◽

Male Meiosis ◽

Meiotic Behaviour ◽

Multiple Sex Chromosomes

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Sex Chromosomes and Psychosis

The British Journal of Psychiatry ◽

10.1192/bjp.153.5.675 ◽

1988 ◽

Vol 153 (5) ◽

pp. 675-683 ◽

Cited By ~ 125

Author(s):

T. J. Crow

Keyword(s):

Sex Chromosomes ◽

Distal Segment ◽

Depressive Illness ◽

Male Meiosis ◽

High Rate ◽

Pseudoautosomal Region ◽

Psychiatric Disease ◽

Same Sex ◽

Y Chromosomes ◽

Gender Influences

Although the incidence of the recurrent psychoses (bipolar affective illness and schizophrenia) in the two sexes is approximately equal, gender influences a number of aspects of major psychiatric disease: unipolar depressive illness is twice as common in females, onset of schizophrenia is earlier and outcome is worse in males, and pairs of psychotic first-degree relatives are more often than expected of the same sex. In addition, sex chromosomal aneuploidies (e.g. XXY and XXX) are more frequent in patients with psychosis. Some of these findings can be explained if there is a major locus of predisposition to psychiatric disease in the ‘pseudoautosomal’ region of the sex chromosomes – that distal segment of the short arms in which there is genetic exchange between X and Y chromosomes at male meiosis. A gene located here would be transmitted in an autosomal manner, but would be passed above chance expectation to children of the same sex when inherited through a male. In that this segment of the sex chromosomes is subject to a high rate of recombination (which could generate new mutations), and may include determinants of brain lateralisation, it appears that the pseudoautosomal region could carry the genes which predispose to the major psychoses.

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Unusual sex chromosome inheritance in mammals

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1970.0042 ◽

1970 ◽

Vol 259 (828) ◽

pp. 15-36 ◽

Cited By ~ 66

Keyword(s):

Sex Determination ◽

Sex Chromosomes ◽

Sex Chromosome ◽

General Pattern ◽

Male Meiosis ◽

Present Knowledge ◽

Microtus Arvalis ◽

Present Contribution ◽

Original Size ◽

Heterogametic Sex

The male has proven to be the heterogametic sex in all mammals studied so far. As is well known, the males usually have the sex chromosomes XY and the females XX. In recent years, however, many exceptions from this general pattern have been discovered. With our present knowledge, the different sex chromosome mechanisms in mammals may be divided into five main groups, and the first of them into subgroups, as follows: (i) Species with XX/XY sex chromosomes: (a) X of original size (see below), Y small; (b) X large, Y small; (c) X large, Y large: (i) end-to-end association of X and Y at male meiosis, (ii) chiasma between X and Y at male meiosis. (ii) Species with XX/XY 1 Y 2 sex chromosomes. (iii) Species with X 1 X 1 X 2 X 2 /X 1 X 2 Y sex chromosomes. (iv) Species with complicated or unknown mechanisms for sex determination. (v) Species with mosaicism of the sex chromosomes, but apparently with an XX/XY mechanism for sex determination. The present contribution will mainly deal with unusual sex chromosome inheritance, that is the groups (ii), (iii) and (iv) above, but the other two groups will also be briefly discussed and examples will be given. Recently Raicu, Kirillova & Hamar (1969) described a new sex chromosome mechanism ( X 1 X 1 X 2 X 2 /X 1 X 2 Y 1 Y 2 ) in the vole Microtus arvalis , but this observation was not confirmed by Schmid (1969), who found an ordinary XX/XY mechanism with both X and Y readily identifiable and of ‘normal’ size, the X comprising 5.6% of ( n A + X) and Y being the smallest chromosome of the complement. Late DNA replication was demonstrated in the allocyclic X and in the Y. Also Wolf (1969) found normal sex chromosomes in this species with no multivalents at male meiosis.

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Sex chromosome pairing mediated by euchromatic homology in Drosophila male meiosis

10.1101/854877 ◽

2019 ◽

Author(s):

Christopher A. Hylton ◽

Katie Hansen ◽

Andrew Bourgeois ◽

John E. Tomkiel

Keyword(s):

Sex Chromosomes ◽

Sex Chromosome ◽

Intergenic Spacer ◽

Male Meiosis ◽

Early Prophase ◽

Dna Breaks ◽

Late Prophase ◽

Prophase I ◽

Y Chromosomes ◽

Meiosis I

ABSTRACTTo maintain proper ploidy, haploid sex cells must undergo two subsequent meiotic divisions. During meiosis I, homologs pair and remain conjoined until segregation at anaphase. Drosophila melanogaster spermatocytes are unique in that the canonical events of meiosis I including synaptonemal complex (SC) formation, double-strand DNA breaks, and chiasmata are absent. Sex chromosomes pair at intergenic spacer sequences within the heterochromatic rDNA while euchromatin is required to pair and segregate autosomal homologies, suggesting that pairing may be limited to specific sequences. However, previous work generated from genetic segregation assays or observations of late prophase I/prometaphase I chromosome associations fail to differentiate pairing from conjunction. Here, we separately examined the capability of X euchromatin to pair and conjoin using an rDNA-deficient X and a series of Dp(1;Y) chromosomes. Genetic assays showed that duplicated X euchromatin can substitute for endogenous rDNA pairing sites. Segregation was not proportional to homology length, and pairing could be mapped to nonoverlapping sequences within a single Dp(1;Y). Using fluorescent in situ hybridization (FISH) to early prophase I spermatocytes, we showed that pairing occurred with high fidelity at all homologies tested. Pairing was unaffected by the presence of X rDNA, nor could it be explained by rDNA magnification. By comparing genetic and cytological data, we determined that centromere proximal pairings were best at segregation. Segregation was dependent on the conjunction protein Stromalin in Meiosis while the autosomal-specific Teflon was dispensable. Overall, our results suggest that pairing may occur at all homologies, but there may be sequence or positional requirements for conjunction.ARTICLE SUMMARYDrosophila males have evolved a unique system of chromosome segregation in meiosis that lacks recombination. Chromosomes pair at selected sequences suggesting that early steps of meiosis may also differ in this organism. Using Y chromosomes carrying portions of X material, we show that pairing between sex chromosomes can be mediated by sequences other than the previously identified rDNA pairing sites. We propose that pairing may simply be homology-based and may not differ from canonical meiosis observed in females. The main difference in males may be that conjunctive mechanisms that join homologs in the absence of crossovers.

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Exaggerated heterochiasmy in a fish with sex-linked male coloration polymorphisms

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1818486116 ◽

2019 ◽

Vol 116 (14) ◽

pp. 6924-6931 ◽

Cited By ~ 36

Author(s):

Roberta Bergero ◽

Jim Gardner ◽

Beth Bader ◽

Lengxob Yong ◽

Deborah Charlesworth

Keyword(s):

Sex Chromosomes ◽

Poecilia Reticulata ◽

Low Frequency ◽

Male Meiosis ◽

Chromosome 12 ◽

Sexually Dimorphic ◽

Recombination Suppression ◽

Physical Maps ◽

Suppressed Recombination ◽

Male Coloration

It is often stated that polymorphisms for mutations affecting fitness of males and females in opposite directions [sexually antagonistic (SA) polymorphisms] are the main selective force for the evolution of recombination suppression between sex chromosomes. However, empirical evidence to discriminate between different hypotheses is difficult to obtain. We report genetic mapping results in laboratory-raised families of the guppy (Poecilia reticulata), a sexually dimorphic fish with SA polymorphisms for male coloration genes, mostly on the sex chromosomes. Comparison of the genetic and physical maps shows that crossovers are distributed very differently in the two sexes (heterochiasmy); in male meiosis, they are restricted to the termini of all four chromosomes studied, including chromosome 12, which carries the sex-determining locus. Genome resequencing of male and female guppies from a population also indicates sex linkage of variants across almost the entire chromosome 12. More than 90% of the chromosome carrying the male-determining locus is therefore transmitted largely through the male lineage. A lack of heterochiasmy in a related fish species suggests that it originated recently in the lineage leading to the guppy. Our findings do not support the hypothesis that suppressed recombination evolved in response to the presence of SA polymorphisms. Instead, a low frequency of recombination on a chromosome that carries a male-determining locus and has not undergone genetic degeneration has probably facilitated the establishment of male-beneficial coloration polymorphisms.

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