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The Genetics of Spontaneous Abortions
Published in Howard J.A. Carp, Recurrent Pregnancy Loss, 2020
Numerical chromosomal abnormalities correlate with advanced maternal age. The explanation is considered to be decreased or absent meiotic recombination. Recombination obligatorily occurs between homologous chromosomes [31–33,35–39], assuring physical proximity between homologous chromosomes if assured until orderly separation (disjunction) that results in two equivalent haploid products. Oocytes ovulated earlier in a woman's reproductive lifespan are believed more likely to have undergone sufficiently robust recombination to render the oocyte/embryo less predisposed to nondisjunction. Again, however, premature chromatid separation in oocytes is an alternate explanation for aneuploidy not usually considered [34].
Genetics of mammalian meiosis
Published in C. Yan Cheng, Spermatogenesis, 2018
In many species including mouse, chromosomal synapsis and meiotic recombination are interdependent. These two processes are tightly coordinated. The synaptonemal complex provides a structural framework for meiotic recombination. Meiotic recombination initiates and stabilizes chromosomal synapsis. Meiotic recombination leads to reciprocal exchange of genetic material between homologous chromosomes (more specifically, between nonsister chromatids). In addition, formation of chiasmata resulting from recombination is essential for faithful segregation of homologous chromosomes during the first meiotic cell division. Meiotic recombination involves a large number of proteins at several distinct stages, which are discussed separately.
Role of telomeres and telomerase in aging and cancer
Published in J. K. Cowell, Molecular Genetics of Cancer, 2003
Jerry W. Shay, Woodring E. Wright, Roger A. Schultz
In Saccharomyces cerevisiae the sole recQ homolog, Sgsl, was identified by virtue of the ability of mutants at this locus to complement the slow growth phenotype of topoisomerase 3 (TOP3) null mutants (top3) (Gangloff et al., 1994). top3 mutants are viable but grow very slowly and selection for ‘slow growth suppression’ (Sgs) yielded sgsl. Independently, Sgsl was identified through a yeast two-hybrid screen for proteins interacting with the c-terminal domain of topoisomerase II (Watt et al., 1995). The chromosome instability seen in sgsl mutants is demonstrated as improper mitotic and meiotic chromosome segregation (Watt et al., 1995). While the mitotic defects have been associated with hyperrecombination of repetitive elements, no increase in meiotic recombination has been observed (Watt et al., 1996). Moreover, although sgsl mutants display premature senescence comparable to that of WS cells, they exhibit no notable defects related to telomere biology. This may reflect fundamental differences between the aging process in higher and lower eukaryotes, with the latter more directly related to rDNA stability (Sinclair and Guarente, 1997).
Long-term exposure to formaldehyde induced down-regulation of SPO11 in rats
Published in Inhalation Toxicology, 2021
Pan Ge, Xiang Zhang, Yan-qi Yang, Mo-qi Lv, Dang-xia Zhou
Spermatogenesis is a continuous process in differentiation and development, and meiosis is an important part of spermatogenesis. The SPO11 gene is a new gene that is highly expressed in testicular germ cells. It is located at chromosome 20 q 13.2–q 13.3, and its protein is highly conserved in evolution. The SPO11 protein is a specific protein for meiosis, which initiates meiotic recombination by mediating double-strand breaks (DSBs) (Bloomfield 2016; Carofiglio et al. 2018). Our previous research also suggested that the SPO11 single nucleotide polymorphism (SNP) (rs28368082) was associated with the risk of non-obstructive azoospermia in Han ethnic populations in Shaanxi, which might be a genetic susceptibility genes for male infertility (Zhang et al. 2011). Moreover, chromosomal recombination failed to be initiated in SPO11–/– mice, and the chromosome agglutination was destroyed, resulting in sperm dysfunction and infertility (Lange et al. 2011). However, the relationship between SPO11 and reproductive toxicity induced by formaldehyde exposure remains unknown.
History of radiation genetics: light and darkness
Published in International Journal of Radiation Biology, 2019
It 1927 Muller first reported that X-ray exposures could increase the frequency of mutations in fruit flies (Muller 1927). In those days, and in fact far beyond the Muller studies, genes were thought to be highly stable and to change only rarely (spontaneous mutations were known), and there was no method to artificially alter gene functions (the fragile nature of the genome was only realized in 1949 when photo-reactivation was discovered: Kelner 1949). The important thing to mention here is not the fact that Muller subjected flies to X-ray exposures, but that he had genetically altered the flies so that the induced mutations could be quantified and transmitted consistently to subsequent generations. Specifically, these studies used a special X chromosome which contained a large inversion. When a female has two normal X chromosomes, meiotic recombination causes an exchange of chromosome segments between the two X chromosomes, and this makes it impossible to determine the origin of mutations that were induced in one X chromosome and to trace the mutations in subsequent generations. In contrast, when the female is heterozygous with an X-chromosome inversion, any single recombination leads to the formation of a dicentric chromosome, and hence cells bearing this are effectively eliminated. If the inversion were more complex (e.g. a second inversion within an inversion), even the probability of a meiotic pairing of homologous chromosomes may be reduced.
Does genome organization matter in spermatozoa? A refined hypothesis to awaken the silent vessel
Published in Systems Biology in Reproductive Medicine, 2018
Dimitrios Ioannou, Helen G. Tempest
Following the onset of puberty, the highly complex and coordinated process of spermatogenesis is designed to generate, and maintain the daily production of millions of fully differentiated spermatozoa throughout the reproductive lifespan of males (De Jonge and Barratt 2006). The process of spermatogenesis usually continues from puberty throughout life and is characterized by a myriad of changes that result in an immature diploid spermatogonium forming four genetically different haploid spermatozoa. This process can be broken down into three sequential elements: (1) mitotic proliferation (producing large numbers of diploid spermatocytes); (2) meiotic recombination and chromosome segregation (producing genetically diverse haploid gametes); and (3) spermiogenesis, whereby round spermatids undergo cytodifferentiation, to repackage the haploid genome for delivery to the oocyte (De Jonge and Barratt 2006). This process happens as a synchronous cycle within the seminiferous epithelium that form an abundance of tubules in the testes. Comparatively speaking, the process of spermatogenesis including the genes involved are highly conserved among species (Bonilla and Xu 2008). However, the duration of the spermatogenesis differs between species (e.g., 35 days in the mouse, 39 days in boars, 42 days in rams, 48 days in goats, 55 days in stallions, 61 days in bulls, and 74 days in humans) (reviewed by (Gonzalez and Dobrinski 2015)). Furthermore, there are species specific differences in the cytodifferentiation process, specifically how the genome is packaged, this will be discussed in more detail in the subsequent section.