Sex chromosomes in land plants can evolve as a consequence of close linkage between the two sex determination genes with complementary dominance required to establish stable dioecious populations, and they are found in at least 48 species across 20 families. The sex chromosomes in hepatics, mosses, and gymnosperms are morphologically heteromorphic. In angiosperms, heteromorphic sex chromosomes ...

Sex chromosomes in crane-fly spermatocytes move polewards at anaphase after the autosomes have reached the poles. In Nephrotoma abbreviate the sex chromosomes are 8um long by 3*5 jitm wide and have two orientations when they move: the long axis of the sex chromosome is either perpendicular or parallel to the spindle axis. We assume (1) that 'when a sex chromosome is perpendicular to the spindle...

Organisms are finely tuned systems that are resilient to perturbations but that must maintain some constants. For example, within the genome, the ratio between different gene products must be tightly constrained to ensure stoichiometric assembly of protein complexes and the like. Evolution has honed expression levels so that as long as there is the same number of chromosomes per cell, the relat...

Canonical ancient sex chromosome pairs consist of a gene rich X (or Z) Chromosome and a male-limited (or female-limited) Y (or W) Chromosome that is gene poor. In contrast to highly differentiated sex chromosomes, nascent sex chromosome pairs are homomorphic or very similar in sequence content. Nascent sex chromosomes can arise if an existing sex chromosome fuses to an autosome or an autosome a...

In humans and other mammals with XX females and XY males, the Y bears a gene (SRY) that induces testis differentiation in the embryo and switches on hormones that masculinize it. The human X has more than 1500 genes, but the tiny Y is a genetic wasteland and bears only 45 protein-coding genes, most active only in testis. To discover how human sex chromosomes got to be so weird, we compared the ...

The two kinds of sex chromosomes in the heterogametic parent are transmitted to offspring with different sexes, causing opposite-sex siblings to be completely unrelated for genes located on these chromosomes. Just as the nest-parasitic cuckoo chick is selected to harm its unrelated nest-mates in order to garner more shared resources, sibling competition causes the sex chromosomes to be selected...

background: chromosome abnormality (ca) including sex chromosomes abnormality (scas) is one of the most important causes of disordered sexual development and infertility. scas formed by numerical or structural alteration in x and y chromosomes, are the most frequently ca encountered at both prenatal diagnosis and at birth. objective: this study describes cytogenetic findings of cases suspected ...

A small cluster of dioecious species in the plant genus Silene has evolved chromosomal sex determination and sex chromosomes relatively recently, within the last 10 million years (MY). Five dioecious Silene species (section Elisanthe) are very closely related (1-2 MY of divergence) and it was previously thought that all five have similar sex chromosomes. Here we demonstrate that in one of these...

Unlike eutherian males, pairing of the sex chromosomes in marsupial males during the first meiotic prophase is not mediated by a synaptonemal complex. Instead, a specific structure, the dense plate, develops during pachytene between the sex chromosomes. We have investigated the development and structural nature of this asynaptic association in males of the marsupial species Thylamys elegans by ...