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Evolutionary Biology of Parasitism
Published in Eric S. Loker, Bruce V. Hofkin, Parasitology, 2023
Eric S. Loker, Bruce V. Hofkin
It is now well appreciated that the pathology imposed by P. falciparum has resulted in the selection of alternative forms of human hemoglobin that confer some protection against malaria. For example, the sickle-cell form of hemoglobin (HbS) differs in sequence from the normal hemoglobin β-chain by just one amino acid (it is a polymorphic variant). Although individuals homozygous for the sickle-cell trait are at high risk for developing sickle-cell anemia (also called sickle-cell disease) and often suffer early mortality, individuals who are heterozygous are 90% less likely to experience severe P. falciparum infections (heterozygote advantage) and are protected by about 30% from complicated malaria, as compared to individuals homozygous for the normal allele. The erythrocytes of heterozygous individuals, once infected, have a greater probability of assuming a jagged, misshapen form (Figure 7.35).
Cystic Fibrosis
Published in Stephen D. Litwin, Genetic Determinants of Pulmonary Disease, 2020
Alexander G. Bearn, Β. Shannon Danes
The frequency of the disease coupled with its lethality raises the question of whether, under certain environmental circumstances, powerful selective forces operate that favor the heterozygote. Indeed it has been suggested that the striking racial variation may have its root cause in the operation of selective factors acting unfavorably in hot climates. Although no convincing evidence for such presumed heterozygous advantage has been advanced, it can be calculated that a mere 2% advantage of the heterozygote is sufficient to achieve genetic equilibrium; the likelihood of being able to identify such a small advantage is remote.
Pertinence between risk of preeclampsia and the renin-angiotensin-aldosterone system (RAAS) gene polymorphisms: an updated meta-analysis based on 73 studies
Published in Journal of Obstetrics and Gynaecology, 2023
Xin Wang, Yujie Kong, Xi Chen, Zhanping Weng, Baolai Li
For AGT M235T, as stratified by race, the 235 T allele increased a greater risk of PE in Caucasians than Mongoloids and Negroids under partial genetic models while no association was detected in mixed race under any model. The over-dominant model was never performed in previous meta-analyses, what puzzled us most was that Caucasians with 235 T allele had 15% reduction (OR = 0.85, 95%CI: 0.76–0.96) risk of PE under over-dominant genetic model, that was to say heterozygous advantage was validated in this model. In stratified analysis by geography, unlike the study from Wang (Wang et al.2020a) showing no association in various regions, our results varied across different genetic models, however, the risk towards of PE was approximate in various regions under dominant and codominant models (MT vs MM), which demonstrated that the MT genotype was a risk factor for PE over MM genotype in these regions. Among the 7 regions, the three genotypes predisposition to PE in East, South and Southeast Asia was highly in accordance with local race (Mongoloids in East Asia and mixed race in South and Southeast Asia) under different genetic models while the outcomes were inconsistent in America and Africa perhaps due to the diversity of race. Hence, the evaluation of AGT M235T polymorphisms and PE risk in these two regions should take race and geography into the consideration collectively.
Psychometric and Faciometric Support for Observable Facial Feminization in Gay Men
Published in Journal of Homosexuality, 2019
Julia M. Robertson, Barbara E Kingsley, Gina C. Ford
A number of these theories have, at their core, the suggestion that phenotypic feminization may be involved. Two such theories involve “balancing selection,” these being heterozygote advantage (sometimes known as “balanced polymorphism” or “overdominance”) and sexually antagonistic selection. In terms of heterozygote advantage, the suggestion is that men heterozygous for homosexual genes may carry a fitness advantage over those homozygous for heterosexual genes. There are a number of possible explanations for this, e.g., through superior sperm competition (MacIntyre & Estep, 1993), enhanced sex drive (McKnight, 1997), or suppressed androgenization with resultantly more feminine personality traits (Miller, 2000; Zeitsch et al., 2008), the latter being a view consistent with female preference for feminized facial features in men (Cunningham, Barbee, & Pike, 1990; Little & Hancock, 2002; Perrett et al., 1998; Rhodes, Hickford, & Jeffrey, 2000). That heterosexual, psychologically feminine men have more opposite-sex sexual partners (Zeitsch et al., 2008) would be consistent with this theory. Similarly, same-sex affiliation theory (Muscarella, 1999, 2000; Rahman & Wilson, 2003) suggests that ancestral men who were more feminine in behavior and who had bisexual preferences would be better adapted to cope with intergroup and intra-sex aggression (a factor in early hominid life, particularly for men) through same-sex affiliations. Additionally, these feminine characteristics would make the men more attractive to women as prospective fathers and partners, in both ways ultimately improving their fitness.
Association of angiotensin receptor 2 gene polymorphisms with pregnancy induced hypertension risk
Published in Hypertension in Pregnancy, 2018
Chenyang Li, Weijun Peng, Heng Zhang, Weirong Yan
The continuous variables of the questionnaire were analyzed by Student’s t-test, and the qualitative factors were performed by Pearson’s χ2 or Fisher exact test. Hardy–Weinberg equilibrium was evaluated by the goodness-of-fit χ2 test. In addition, a logistic regression approach was used to estimate the effects of AT2R gene polymorphisms under dominant, recessive, co-dominant and heterozygous advantage models. Phase 2.0 software was applied to build haplotypes of AT2R gene, odd ratio (OR) and 95% confidence interval (CI) values of the haplotypes were obtained by logistic regression. Except the construction of AT2R gene haplotypes, all the analyses were performed by SPSS20.0. A two-tailed p value of <0.05 was considered significant.