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Genetics and exercise: an introduction
Published in Adam P. Sharples, James P. Morton, Henning Wackerhage, Molecular Exercise Physiology, 2022
Claude Bouchard, Henning Wackerhage
Two important events of meiosis contribute to human genetic diversity: Independent assortment of chromosomes. Of each chromosome pair in somatic cells, gametes receive only one chromosome. Is it the mothers or fathers chromosome? This is a random process and so each spermatocyte or oocyte will have a random combination of chromosomes from maternal and paternal origins.Homologous recombination. During meiosis, before chromosomes migrate to daughter cells, chromosomes cross over and exchange equivalent segments. For instance, a crossing over may occur between maternal and paternal chromosome 3, resulting in an exchange of DNA between the two chromosomes. About 50–60 recombinations take place between all pairs of homologous chromosomes (i.e. pairs of chromosomes of maternal and paternal descent) during meiosis.
The Host Response to Grafts and Transplantation Immunology
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
MHC antigens are inherited en bloc by offspring. As shown in Figure 11.4, each parent has a pair of homologous chromosomes, each encoding an HLA haplotype. Haplotype refers to the set of MHC genes, one from each locus, encoded on one of the homologous chromosomes. The offspring inherit one haplotype from each parent. Therefore, children inherit one of four possible combinations. The genes are closely linked on the chromosome and crossing over occurs infrequently (~1 percent). Crossing over occurs when genetic material is exchanged between chromosomes during meiosis.
The Fight Against Cancer
Published in Nathan Keighley, Miraculous Medicines and the Chemistry of Drug Design, 2020
The daughter cells, produced after cell division, will now have the correct genetic information for controlling cellular processes. There are two forms of cell division: mitosis and meiosis. Mitosis produces two daughter cells and enables cells to replicate for growth and repair. Meiosis produces four daughter cells, each with half the number of chromosomes: haploid cells, which are important for making gametes, which fuse during fertilisation to make diploid cells, and ultimately a foetus.
Heterochromatin extension: a possible cytogenetic fate of primary amenorrhea along with normal karyotype
Published in Journal of Obstetrics and Gynaecology, 2022
Bishal Kumar Dey, Shanoli Ghosh, Ajanta Halder, Somajita Chakraborty, Sanchita Roy
The region of heterochromatin also acts as a key part in chromosome structure, histone modification and gene regulation. There is evidence from where we come to know that there may be displacement of heterochromatin from one chromosome to another. Perhaps, this displacement is helping in the extension of a particular chromosome at the heterochromatin portion of the long arm (Bannister and Kouzarides 2011). The mechanisms of spindle fibres, chromosome movement, meiosis crossover and change of sister chromatids are considered to be the integral region as heterochromatin for a chromosome. At the time of meiosis, there may be a change in area of synapses of homologous chromosomes in the polymorphic heterochromatin region. The heterochromatin in chromosomal polymorphism can also regulate gene expression by reversible transformation between heterochromatin (non-coding DNA sequences) and euchromatin (expressed DNA sequences) thus justifying certain clinical expression like short stature or PA. It was also postulated that defective histone protein methylation due to presence of heteromorphic variants may play a more crucial role in ovarian failure. Association of heterochromatin polymorphism with ovarian dysgenesis may be a reason for the occurrence of PA. For that, we need to study on a greater number of patients on the basis of their nucleosome’s functionality and heteromorphic polymorphism by sequencing.
Genetic variations as molecular diagnostic factors for idiopathic male infertility: current knowledge and future perspectives
Published in Expert Review of Molecular Diagnostics, 2021
Mohammad Karimian, Leila Parvaresh, Mohaddeseh Behjati
Balanced chromosomal translocations involve the breakage of two chromosomes and abnormal repair of chromosomal fragments resulting in the transfer of genetic material from one chromosome to another without loss of any genetic material. In vast majority of cases, carriers of balanced translocations are phenotypically normal, unless one of the breakpoints at the site of translocation disrupts an important gene. Chromosomal translocation, while phenotypically normal, may experience fertility loss, miscarriage, or birth defects. Normal meiotic segregation of these translocations in gametes can lead to duplication or deletion of chromosomal regions involved in translocation [171]. Like chromosomal translocations, inversions can lead to infertility, miscarriage, and birth defects. During meiosis, chromosomes are forced to form specialized structures, so that homologous chromosomes can be paired. Chromosomal inversions can affect these specialized structures. Research on the production of unbalanced gametes in balanced inversion carriers has been done to a much lesser extent than translocations. However, a handful of studies have reported an unbalanced sperm range of 1–54% [172–174].
Genetic analysis of embryo in a human case of spontaneous oocyte activation: a case report
Published in Gynecological Endocrinology, 2020
Yuanyuan Ye, Na Li, Xiaohong Yan, Rongfeng Wu, Weidong Zhou, Ling Cheng, Youzhu Li
Meiosis is a complicated process that is vital for fertility and reproduction. During the reproductive cycle, a surge of luteinizing hormone (LH) from the pituitary or external source triggers the resumption of meiosis and its progression to metaphase II (MII). After a series of changes including chromosome condensation, spindle formation and extrusion of the first polar body, the oocyte enters meiosis II and again gets arrested at metaphase II stage until fertilization [1,2]. Meiosis II is completed after sperm injection for 2–13 h, the second polar body is extruded and the oocyte and sperm chromosomes each become confined within a pronucleus, producing two abutting pronuclei in a zygote [3,4]. Eighteen to thirty-one hours after fertilization, the pronucleus disintegrates and disappears, and the embryo undergoes a series of cleavage divisions.