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Human physiology, hazards and health risks
Published in Stephen Battersby, Clay's Handbook of Environmental Health, 2023
Revati Phalkey, Naima Bradley, Alec Dobney, Virginia Murray, John O’Hagan, Mutahir Ahmad, Darren Addison, Tracy Gooding, Timothy W Gant, Emma L Marczylo, Caryn L Cox
For a second reason why epigenetics matters let’s go back to biological sex again. All the gametes from the mother will carry an X chromosome but that from the father will carry an X or Y. The sex chromosome from the father that ends up in the zygote will therefore define biological sex, X for a female and Y for a male. Now consider gene dosage. The best way of thinking about this is to consider a disease where gene dosage is abnormal, and for the purposes of this chapter we can consider Down’s syndrome as an example. In the common form of Down’s syndrome there is an additional copy of chromosome 21, so there are three copies. This means there is differential expression of some genes encoded or controlled by genes on chromosome 21, leading to the characteristic phenotype [7]. Returning to the X chromosome, why is it then that females do not have a gene dosage effect from their additional X chromosome compared to males that have only one X chromosome but are equally dependent on the X chromosome genes? The answer lies in epigenetics. Within each cell of a female one copy of the X chromosome is turned off through the process of epigenetic X chromosome inactivation. This suppression is random so that in any one cell of a female the X chromosome from either the father or the mother is inactivated via DNA methylation [8].
Radiation and man
Published in R.J. Pentreath, Nuclear Power, Man and the Environment, 2019
Alterations (mutations) to the genes on a chromosome are classified, for convenience, as being either dominant or recessive, depending upon the extent to which the effect is expressed in an offspring which inherits the mutated gene from one parent only. Thus a mutation which is fully dominant will have an effect if inherited from one parent only, whereas a fully recessive mutation has no effect unless the same mutated gene is received from both parents. The only exception is when one mutated gene is associated with the female chromosome. It was stated above that the chromosomes are paired with the exception of the sex chromosomes. Women have 23 matched pairs of chromosomes but in men the 23rd pair do not match. Instead of two large X chromosomes (XX) there is a large X and a small Y chromosome (XY). The Y chromosome carries the gene for maleness and is dominant over the X chromosome. Sperm may have either the X or the Y chromosome, whereas all ova have the X chromosome, and thus all resulting embryos receive at least one X chromosome. The relevance of this is that the X chromosome carries a number of genes which have nothing to do with characteristics of sex, whereas the Y chromosome does not.
Soft X-ray Tomography: Techniques and Applications
Published in Paolo Russo, Handbook of X-ray Imaging, 2017
Axel A. Ekman, Tia E. Plautz, Jian-Hua Chen, Gerry McDermott, Mark A. Le Gros, Carolyn A. Larabell
An example of correlated whole-cell SXT–fluorescence imaging is the work by Smith et al. (2014) characterizing the inactive X-chromosome. Female mammals inherit an X-chromosome from each parent, whereas males only inherit a single X-chromosome from their mother. To prevent an imbalance of X-chromosome gene products, one X-chromosome (Xi) must be “silenced” in every female cell. This phenomenon is the pinnacle of epigenetic regulation and has been the subject of intense study since its discovery in the mid-1900s (Barr and Bertram 1949, Lyon 1961). Before the correlated SXT study, the topology and degree of compaction adopted by Xi were open questions, since neither could be determined accurately using the existing imaging techniques. In the study by Smith et al. (2014), cryogenic fluorescence tomography (CFT) data allowed for localization of Green fluorescent protein (GFP)-labeled Xi in the nucleus of female lymphoma cells whereas SXT provided the cellular structure. The presence of fiducial markers visible in both modalities allowed accurate overlay of the two tomographic reconstructions (Figure 40.21).
GPR61 methylation in cord blood: a potential target of prenatal exposure to air pollutants
Published in International Journal of Environmental Health Research, 2022
Feifei Feng, Li Huang, Guoyu Zhou, Jia Wang, Ruiqin Zhang, Zhiyuan Li, Yawei Zhang, Yue Ba
DNA methylation, a key mode of epigenetic regulation, is essential for silencing retroviral elements, regulating gene expression and cell differentiation, genomic imprinting, and X chromosome inactivation (Moore et al. 2013). In mammals, genome methylation patterns are reprogrammed during at least two developmental periods in germ cells and in preimplantation embryos (Reik et al. 2001; Reik 2007). Although it has been reported that environmental effect such as air pollution, malnutrition, and toxicants may play important roles in epigenetic changes(Burris and Baccarelli 2017; Yu et al. 2020), DNA methylation patterns in somatic differentiated cells are generally stable and heritable (Reik et al. 2001). Thus, changes in DNA methylation that occur in utero may be an important reason of the fetal origin of diseases (Chmurzynska 2010). Indeed, studies have demonstrated that placental DNA methylation changes might mediate reproductive and developmental toxicity induced by PM (Ciaula and Bilancia 2015; Cai et al. 2017). However, the current evidence appears insufficient to demonstrate an effect of air pollutants exposure during gestation on DNA methylation.
Why human germline genome editing is incompatible with equality in an inclusive society
Published in The New Bioethics, 2021
Furthermore, it should be recognized that any change to the genetic variables in the creation of an individual results in a very different person coming into existence. For example, if the X chromosome in a sperm cell, used to fertilize an egg to give an embryo containing XX chromosomes, is exchanged for a Y chromosome, then the individual resulting from this substitution would be completely different to the one who would, otherwise, have existed. The resulting boy (with XY chromosomes) would have a completely different life to that of the girl (with XX chromosomes) who would, otherwise, have existed. Similarly, if it is not whole chromosomes but just another part of the DNA of the sperm or egg cells, as well as very early embryos, that is genetically modified in the bringing into existence of a person, a new individual would be brought into being who is completely different to the one who would, otherwise, have existed without the modification.6
How the quest to improve sheep reproduction provided insight into oocyte control of follicular development
Published in Journal of the Royal Society of New Zealand, 2018
The original ewe, A281, carrying the Inverdale mutation was incorporated into a newly established high fecundity flock in 1979 (Davis et al. 1991, 1995). While this ewe did not fit the original specification for the flock, as she was a commercial flock ewe of mixed breeding with unknown parentage, her subsequent lifetime lambing record was exceptional. During her lifetime she had 33 lambs over 11 lambings including two sets of twins, seven sets of triplets and two sets of quadruplets. Breeding trials established the location of the gene on the X-chromosome, as males carrying the mutation did not produce carrier sons (Davis et al. 1991). In addition, the variation in the ovulation rate of daughters of a carrier ram was less than would be expected if the gene was autosomal where half the daughters would be heterozygous for the gene.