Search results for "Chromosome pair"
showing 3 items of 3 documents
Centromere-Like Elements in Megaselia Spiracularis (Diptera: Phoridae): A Fine-Structure and Cytogenetic Study
2004
The present study was concerned with the karyotype of a humpbacked fly, Megaselia spiracularis (Diptera: Phoridae). Chromosome preparations of neuroblasts isolated from male and female pupae uniformly showed two pairs of metacentric chromosomes and a telocentric chromosome pair. All chromosomes were homomorphic. The analysis of ultrathin serial sections through spermatogonia in metaphase using transmission electron microscopy, confirmed the presence of 3 regular chromosome pairs. In ultrathin sections, the centromeres could be detected as individual elements owing to their lesser electron density in comparison with the chromosome arms. In addition, the spindles contained two tiny elements s…
Retroelements: tools for sex chromosome evolution
2003
Many eukaryotic taxa inherit a heteromorphic sex chromosome pair. It is a generally accepted hypothesis that the sex chromosome pair is derived from a pair of homologous autosomes that has developed after the occurrence of a sex differentiator in an evolutionary process into two structurally and functionally different partners. In most of the analyzed systems the occurrence of the dominant sex differentiator is paralleled by the suppression of recombination within and close by that region. The recombinational isolation can spread in an evolutionary selection process from neighboring regions finally over the whole chromosome. Suppression of recombination strongly biases the distribution of r…
A high incidence of meiotic silencing of unsynapsed chromatin is not associated with substantial pachytene loss in heterozygous male mice carrying mu…
2009
Meiosis is a complex type of cell division that involves homologous chromosome pairing, synapsis, recombination, and segregation. When any of these processes is altered, cellular checkpoints arrest meiosis progression and induce cell elimination. Meiotic impairment is particularly frequent in organisms bearing chromosomal translocations. When chromosomal translocations appear in heterozygosis, the chromosomes involved may not correctly complete synapsis, recombination, and/or segregation, thus promoting the activation of checkpoints that lead to the death of the meiocytes. In mammals and other organisms, the unsynapsed chromosomal regions are subject to a process called meiotic silencing of…