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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].
Toxic Responses of the Female Reproductive System
Published in Stephen K. Hall, Joana Chakraborty, Randall J. Ruch, Chemical Exposure and Toxic Responses, 2020
Joana Chakraborty, Maureen McCorquodale
When the blood sample arrives in the laboratory, the white cells are grown in culture and after three days are treated with a chemical which arrests cell division in a stage called metaphase where the chromosomes are most easily studied since the individual features are clearly observable with a microscope at this state. The cells are then burst open, the chromosomes are released on a microscope slide, stained, photographed, enlarged, cut out and then arranged into a specific pattern on a sheet of paper. The arrangement of the chromosomes is called a karyotype and is based on the size and shape of the chromosomes as well as on the specific pattern of bands found on each chromosome. A normal karyotype consists of 46 chromosomes in 23 pairs. The autosomes (nonsex chromosomes) are numbered 1 to 22, and the sex chromosomes consist of two X chromosomes for a female and an X and Y chromosome for a male (Figures 12.3 and 12.4).
Environmental Disease
Published in Gary S. Moore, Kathleen A. Bell, Living with the Earth, 2018
Gary S. Moore, Kathleen A. Bell
Other genetic diseases are inherited as autosomal recessive, which means that a defective gene must occur in both chromosomes at complementary sites in order for the disease to be expressed. It also means that both parents, if healthy, were each carriers of the defective gene, which they passed along to the child. A person with this type of genetic disease is deprived of an essential protein resulting in a potentially severe disease, such as PKU or CF.27 There are also dominant and recessive defective genes on the sex chromosomes as well, producing a variety of sex-linked diseases, including hemophilia-A, color blindness, and forms of muscular dystrophy. Since males have one copy of the Y-chromosome, even recessive sex-linked genetic diseases are expressed in men, as there is no other allele to mask the defect.
Gene drive to reduce malaria transmission in sub-Saharan Africa
Published in Journal of Responsible Innovation, 2018
Austin Burt, Mamadou Coulibaly, Andrea Crisanti, Abdoulaye Diabate, Jonathan K. Kayondo
Maleness in Anopheles mosquitoes is thought to be determined by a dominant gene on the Y chromosome (Krzywinska et al. 2016). Males have X and Y sex chromosomes, and females have two Xs. Normally, the X and Y chromosomes of a male are transmitted 50:50 to the next generation, but if there is a gene causing the Y chromosome to be preferentially transmitted, then there will be a preponderance of male offspring. If the gene responsible is on the Y chromosome, then it too will be preferentially transmitted, and, all else being equal, it will spread through the population, replacing the normal Y. As it does so, the population as a whole will become male-biased. This is a driving Y chromosome.