Cell division
Frank J. Dye in Human Life Before Birth, 2019
When crossing over occurs, new combinations of genes are created (recombination). For example, let us designate the four chromatids in a single pair as M, M, D, and D, two coming from each parent. Before crossing over, the two M sister chromatids and the two D sister chromatids in each chromosome pair are identical; recall chromatid replication during S stage. After crossing over, we are likely to have M, M/D, D/M, and D. Whereby we initially had two kinds of chromatids genetically, we now have four kinds of chromatids genetically. In other words, genetic diversity has been increased. If the meiosis was involved in egg production, now four kinds are possible rather than the two kinds possible before crossing over. The same is true for sperm production.
Mobile DNA Sequences and Their Possible Role in Evolution
S. K. Dutta in DNA Systematics, 2019
In some cases, the transposon-dependent deletions can appear as a result of unequal crossing over rather than of nonprecise excision. One may suggest that if two similar transposons are located in the different but close sites on the chromosome, the unequal crossing over would occur leading to small deletions or tandem duplications. Unequal crossing over was demonstrated in the case of mdg BEL160 and for the FB-element161 inserted into the white locus, as well as in the case of Ty1 in the yeast.162 Unequal crossing over is known to play an important role in the initial stages of evolution. More frequently the excised transposon is then lost, but sometimes it may be inserted at another site on chromosomes, inducing further genome reorganization.7,35,101,148
Preimplantation Genetic Testing for Structural Rearrangements
Carlos Simón, Carmen Rubio in Handbook of Genetic Diagnostic Technologies in Reproductive Medicine, 2022
Inversions are rearrangements that occur after a double intrachromosomal break, 180° rotation of the fragment located between two breakpoints, and subsequent insertion of the fragment into the chromosome. During normal meiosis, crossing over must occur to ensure orderly disjunction. In inversions, this process must occur within the inverted segment [21]. Carriers of inversions are at risk of having offspring with unbalanced karyotypes, and this risk depends on the implicated chromosome and length of the inverted segment [33]. The chance of recombination may increase when the size of the inverted fragment accounts for more than 30% of the whole chromosome, and there may be a high risk of producing aneuploid embryos when the size of the inverted fragment is at least 100 Mb or over 50% [34,35].
A rare Y-autosome translocation found in a patient with nonobstructive azoospermia: Case report
Published in Systems Biology in Reproductive Medicine, 2021
Anita Barišić, Alena Buretić Tomljanović, Nada Starčević Čizmarević, Saša Ostojić, Pavle Romac, Jadranka Vraneković
Furthermore, pericentric inversion 9 is the most common inversion seen in humans, with an overall frequency of approximately 1.6% (Šípek et al. 2015). Although this region is inert in nature, reproductive disorders in some carriers have been reported. This can be explained by a disruption in meiosis I that may result in unbalanced gametes (Pinho et al. 2005). Disruptions arise during crossing over from the formation of recombinant chromosomes between the normal and inverted homolog of chromosome 9 (McKinlay Gardner et al. 2018), leading to early miscarriages or live births with various anomalies. However, literature reporting on reproductive risks associated with this population variant is controversial (Merrion and Maisenbacher 2019). Regardless, when combined with the aforementioned translocation, it should be considered as an additional predisposing factor for infertility.
Genetic investigation and phylogenetic analysis of three Chinese ethnic groups using 16 X chromosome STR loci
Published in Annals of Human Biology, 2020
Ruiyang Tao, Jingyi Zhang, Ruocheng Xia, Zihao Yang, Shouyu Wang, Xiaochun Zhang, Qi Yang, Suhua Zhang, Chengtao Li
Detailed information for the 16 X-STR loci and amelogenin contained in the kit are summarised in Supplementary Table S1. Among the three ethnic groups, no statistically significant departure from HWE was observed. Furthermore, the genotyping results did not provide any evidence of LD in any pairs of the 16 X-STR loci in the Tibetan, Mongolian and Kazakh groups (Supplementary Table S2) after adjusting for multiple testing (p = .05/120), consistent with the results reported by Liu et al. in the Han population of Henan (Liu et al. 2016). That is to say, recombination and crossing-over might happen within these loci. This suggests that, in the ethnic groups from this study, allelic frequencies from these 16 X-STR loci should be adopted for forensic applications instead of haplotype frequencies.
What’s the latest with investigational drugs for soft tissue sarcoma?
Published in Expert Opinion on Investigational Drugs, 2022
Elena Cojocaru, Andrea Napolitano, Cyril Fisher, Paul Huang, Robin L Jones, Khin Thway
The phase 3 trial APROMISS compared dacarbazine vs anlotinib in patients with synovial sarcoma, randomized in a 1:2 ratio [49]. Patients had the option of crossing over on the progression of their disease and the results were presented at the ASCO meeting in 2021. A total of 79 participants received treatment with either dacarbazine or anlotinib and the PFS was statistically significant in the anlotinib arm, at 2.89 months compared to 1.64 months in the control arm with dacarbazine. Although the duration of PFS was not remarkably longer, the number of patients with a prolonged PFS was significantly higher in the anlotinib arm at 4, 6 and 12 months compared to dacarbazine (48.1%, 42.3% and 26.0% compared to 14.85%, 11.1% and 3.7%). The study has completed accrual for synovial sarcoma and leiomyosarcoma and is currently recruiting patients with alveolar soft part sarcoma. More ongoing trials are currently studying the combination of anlotinib with other active drugs in the treatment of sarcomas such as nivolumab, (NCT04165330), pegylated liposomal doxorubicin (NCT 04765228) or toripalimab (NCT04172805).