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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.
When sex matters: a complete model of X-linked diseases
Published in International Journal of General Systems, 2018
C. Del Vecchio, F. Verrilli, L. Glielmo
A genetic disorder is defined as an illness caused by abnormalities within the DNA sequence of human genes. Although genetic diseases are very rare, it has been estimated that millions of people are affected worldwide (Word Health Organisation 2015). X-linked recessive diseases include the severe diseases haemophilia A, Duchenne/Becker muscular dystrophy, and Lesch–Nyhan syndrome as well as common and less serious conditions such as male pattern baldness and red-green colour blindness. The incidence of an X-linked recessive disease depends on the disorder's severity: it ranges from 1 in 3000 newborn males for Duchanne muscular dystrophy to 1 in 20 for the red and green colour blindness. Despite such relevance, only a few mathematical models have been specifically developed to study the dynamics and spread of X-linked recessive diseases in a population (Yeghiazarian 1999; Del Vecchio, Glielmo, and Corless 2014; Verrilli et al. 2017). The Hardy–Weinberg (HW) law is a cornerstone for these studies. Under specific assumptions – i.e. infinite population size, random mating, no selection, no migration, no mutation, and equal initial genotype frequencies in the two sexes – the HW law allows one to predict the genotype frequencies in the next generations. However, the stringent hypotheses of the law limit its applicability in epidemiological studies. Other genetic population models have been subsequently developed, relaxing some of the HW principle's assumption. Related studies analysed the inheritance mechanism of any gene – not necessarily responsible for a genetic disease – placed on the X chromosome (Lange 1982; Lange and Redelings 2002); they belong to the field of population genetics. Even in more generic scenarios (i.e. not specifically designed for X-linked recessive diseases), contributions seldom examine the combined effects of selection and mutation on population's dynamics and equilibrium (see Nagylaki 1977; Szucs 1991).