North African genes in Iberia studied by Y-chromosome DNA haplotype 5.

The frequency of haplotype 5 at the Y-chromosome-specific DNA polymorphism (p49/TaqI) was reported in a study of 487 males originating from five different geographic locations in Iberia and North Africa. The highest frequency of haplotype 5 (68.9%) was previously observed in Berbers from Morocco, and it has been established that this haplotype is a characteristic Berber haplotype in North Africa. The relative frequencies of haplotype 5 distribution show a geographical gradient of decreasing frequency according to latitude in Iberia: 40.8% in Andalusia, 36.2% in Portugal, 12.1% in Catalonia, and 11.3% in the Basque Country; such a cline of decreasing frequency of haplotype 5 from the south to the north in Iberia clearly establishes a gene flow from North Africa towards Iberia.     

Phylogeography of the African buffalo based on mitochondrial and Y-chromosomal loci: Pleistocene origin and population expansion of the Cape buffalo subspecies

Population genetics and phylogeography of the African buffalo (Syncerus caffer) are inferred from genetic diversity at mitochondrial D-loop hypervariable region I sequences and a Y-chromosomal microsatellite. Three buffalo subspecies from different parts of Africa are included. Nucleotide diversity of the subspecies Cape buffalo at hypervariable region I is high, with little differentiation between populations. A mutation rate of 13-18% substitutions/million years is estimated for hypervariable region I. The nucleotide diversity indicates an estimated female effective population size of 17 000-32 000 individuals. Both mitochondrial and Y-chromosomal diversity are considerably higher in buffalo from central and southwestern Africa than in Cape buffalo, for which several explanations are hypothesized. There are several indications that there was a late middle to late Pleistocene population expansion in Cape buffalo. This also seems to be the period in which Cape buffalo evolved as a separate subspecies, according to the net sequence divergence with the other subspecies. These two observations are in agreement with the hypothesis of a rapid evolution of Cape buffalo based on fossil data. Additionally, there appears to have been a population expansion from eastern to southern Africa, which may be related to vegetation changes. However, as alternative explanations are also possible, further analyses with autosomal loci are needed.     

Conception date affects litter type and foetal sex ratio in female moose in Estonia

1.  The Trivers–Willard model of optimal sex ratios predicts that in polygynous species mothers in better condition should produce more male than female offspring. However, empirical support for this hypothesis in mammals and especially ungulates has been equivocal. This may be because the fitness of mothers has been defined in different ways, reflecting morphological, physiological or behavioural measures of condition. In addition, factors other than maternal condition can influence a mother's fitness. Given that recent studies of wild ungulates have demonstrated the importance of the timing of conception and birth on offspring fitness, litters conceived at different stages of the rut might be expected to exhibit differences in types and embryonic sex ratio.
2.  Based on a 6-year survey of the reproductive tracts of female moose harvested in Estonia, we investigated the effect of conception date on the types of litters produced and on the foetal sex ratio.
3.  There was a clear relationship between conception date and litter characteristics. Overall, earlier conceived litters were more likely than those conceived late to contain multiple embryos and a high proportion of males. However, while foetal sex ratio varied nonlinearly with conception date in yearlings and subadults, no relationship was found in adults.
4.  We conclude that female moose adjust foetal sex ratio and litter type/size depending on their age and the date of conception, and that these adjustments are in accordance with the Trivers–Willard hypothesis if females that conceive earlier are in better condition.     

Timing of foetal growth spurts can explain sex ratio variation in polygynous mammals

The prediction from sex ratio theory that natural selection on sexually dimorphic mammals should favour an excess of male offspring only when mothers are in good condition, has been tested extensively but with little consistency in results. Although recent studies have shown that environmental variations may cause some of the discrepancy, there have also been reports of contrasting sex ratios under similar environmental settings. Here it is suggested that variation in timing of environmental stress and sex-specific differences in foetal growth pattern in relation to maternal condition, may explain such seeming contradictions in sex ratio variation of polygynous mammals.     

Environmental sex reversal,Trojan sex genes,and sex ratio adjustment: conditions and population consequences

The great diversity of sex determination mechanisms in animals and plants ranges from genetic sex determination (GSD, e.g. mammals, birds, and most dioecious plants) to environmental sex determination (ESD, e.g. many reptiles) and includes a mixture of both, for example when an individual’s genetically determined sex is environmentally reversed during ontogeny (ESR, environmental sex reversal, e.g. many fish and amphibia). ESD and ESR can lead to widely varying and unstable population sex ratios. Populations exposed to conditions such as endocrine‐active substances or temperature shifts may decline over time due to skewed sex ratios, a scenario that may become increasingly relevant with greater anthropogenic interference on watercourses. Continuous exposure of populations to factors causing ESR could lead to the extinction of genetic sex factors and may render a population dependent on the environmental factors that induce the sex change. However, ESR also presents opportunities for population management, especially if the Y or W chromosome is not, or not severely, degenerated. This seems to be the case in many amphibians and fish. Population growth or decline in such species can potentially be controlled through the introduction of so‐called Trojan sex genes carriers, individuals that possess sex chromosomes or genes opposite from what their phenotype predicts. Here, we review the conditions for ESR, its prevalence in natural populations, the resulting physiological and reproductive consequences, and how these may become instrumental for population management.     

Crowding, sex ratio and horn evolution in a South African beetle community

Sexually selected ornaments and weapons are exceptionally variable, even between closely related species. It has long been recognized that some of this diversity can be explained by differences in mating systems between species, but there remains substantial variation between species with similar mating systems. We investigated the roles of sex ratio (measured as operational sex ratio, OSR) and population density (measured as mean male crowding, a measure indicating the average number of conspecific males that an individual male animal will encounter) in determining horn presence in a community of South African dung beetles. Analysis of data from 14 species using a generalized least-squares model incorporating phylogenetic influences found that both OSR and mean crowding were significant predictors of horn presence, with hornless species tending to show female-biased sex ratios and high levels of crowding. The influence of mean crowding on horn diversity between species probably reflects the difficulty of guarding and monopolizing females when many competitors are present, meaning that males who adopt 'scramble' tactics tend to be favoured.     

Direct and indirect estimation of the sex ratio of mutation frequencies in hemophilia A.

Carrier detection tests were carried out in 119 families with hemophilia A by using the data obtained with current DNA techniques (e.g., RFLP analysis and direct identification of mutations), conventional carrier detection tests (e.g., factor VIII:C and von Willebrand factor antigen), and pedigree information. On the basis of this data, we estimated the sex ratio of mutation frequencies with three completely different methods and compared the results. Since the classical indirect method derived from Haldane is substantially influenced by reproductive fitness (f), the sex ratio of mutation frequencies was estimated for both f = .3 and f = .5, resulting in a male:female mutation ratio of 5.37 (95% confidence interval 2.16-13.02) and 3.26 (95% confidence interval 0.97-8.73), respectively. According to the equilibrium-independent indirect method formulated by Rosendaal et al., the male:female ratio was estimated to be 3.4 (95% confidence interval 1.18-8.81). Since current DNA techniques provide information on the grandparental origin of the patient''s X chromosome, we were twice able to estimate directly the male:female mutation ratio as 15:1, by using the quotients of mutation origin (maternal grandfather/maternal grandmother and maternal grandfather/patient''s mother, respectively). Application of the Fisher test shows that the male mutation rate is higher than the female rate (P = 8.55 x 10(-7). Since all three completely different approaches unequivocally showed a higher male than female mutation frequency, this should be considered to be an established fact in calculating the risk in hemophilia A families.     

Operational sex ratio in terrestrial isopods: interaction between potential rate of reproduction and Wolbachia-induced sex ratio distortion

Selfish genetic elements distorting sex ratio are known in several arthropods. By inducing a deficit of males, these sex ratio distorters may modify sexual selection by reversing the sex that competes for a mate. They also have potential to reduce the male proportion to values limiting mating possibilities and therefore limiting population size. Wolbachia endosymbionts are intracytoplasmic, vertically transmitted bacteria that convert genotypic males of terrestrial isopods (woodlice) into functional females. We have tested the impact of these feminizing symbionts on the operational sex ratio (OSR) in three woodlice species. Preliminary experiments consisted in estimating the potential rate of reproduction in males and females, and measuring the dynamics of the onset of reproduction in the wild. These parameters were then combined with population sex ratio to discriminate key factors influencing the OSR. The results suggest that the high potential rate of reproduction of males and the asynchrony in female receptivity both counterbalance female-biased sex ratios. The result is an overall balanced or slightly female-biased OSR. Male deficit can therefore not be considered as a factor strongly limiting reproduction in woodlice. Some females were nevertheless found not mated in the wild at the beginning of the reproductive season, most of them being infected by Wolbachia . This suggests that uninfected females may have an advantage as the first mate. Consequences of these findings on woodlice population dynamics are discussed.     

Association test algorithm between a qualitative phenotype and a haplotype or haplotype set using simultaneous estimation of haplotype frequencies, diplotype configurations and diplotype-based penetrances

Analysis of the association between haplotypes and phenotypes is becoming increasingly important. We have devised an expectation-maximization (EM)-based algorithm to test the association between a phenotype and a haplotype or a haplotype set and to estimate diplotype-based penetrance using individual genotype and phenotype data from cohort studies and clinical trials. The algorithm estimates, in addition to haplotype frequencies, penetrances for subjects with a given haplotype and those without it (dominant mode). Relative risk can thus also be estimated. In the dominant mode, the maximum likelihood under the assumption of no association between the phenotype and presence of the haplotype (L(0max)) and the maximum likelihood under the assumption of association (L(max)) were calculated. The statistic -2 log(L(0max)/L(max)) was used to test the association. The present algorithm along with the analyses in recessive and genotype modes was implemented in the computer program PENHAPLO. Results of analysis of simulated data indicated that the test had considerable power under certain conditions. Analyses of two real data sets from cohort studies, one concerning the MTHFR gene and the other the NAT2 gene, revealed significant associations between the presence of haplotypes and occurrence of side effects. Our algorithm may be especially useful for analyzing data concerning the association between genetic information and individual responses to drugs.     

Interactions between tassel seed genes and other sex determining genes in maize

The tassel seed mutations of maize cause sex reversal of the florets of the tassel, such that the normally staminate florets develop pistils. Although these mutations have been recognized for many years, little is known about how they act. We have tested the hypothesis that the tassel seed genes interact directly with each other and with other genes controlling sex determination in a single genetic pathway by the construction and analysis of double mutants. On the basis of the phenotypes of the double mutants, the tassel seed mutations were placed into two groups: ts1, ts2, Ts5 and ts4, Ts6. Both groups of tassel seed mutations were additive with the masculinizing mutation dwarf, indicating independent modes of action. Interactions of tassel seed mutations with silkless varied, allowing the ordering of the action of the various tassel seed mutations relative to silkless. Both groups of tassel seed mutations were epistatic with regard to sex expression to mutations that alter both architecture of the plant and distribution of male and female florets, Teopod 1, terminal ear, and teosinte branched. Thus, there are at least two separate genetic pathways that control the sex of florets in maize tassels. In addition, analysis of double mutants revealec that all tassel seed genes tested play a role in the regulation of flower morphogenesis as well as pistil suppression. © 1994 Wiley-Liss, Inc.     

HLA antigen,gene, and haplotype frequencies in Thailand

Summary Antigen, gene, and haplotype frequencies as well as phenotype distribution of the HLA system were studied in a series of 213 individuals in northern Thailand. The series consisted of 160 northern Thais, 23 Thai individuals from various other regions of Thailand, and 25 persons of Chinese origin. Most frequently found were the alleles HLA-A11 and HLA-Bw40 and the haplotype HLA-A2, B-. Phenotype distribution followed a Hardy-Weinberg expectation. Significant differences were found especially between our results for the alleles of locus B and the results of a series from Bangkok reported by Chiewsilp and Chanarat (1976).     

Variation in sex ratio between progeny groups in dairy cattle

Summary Highly significant differences between progeny groups have been found in the Israeli-Frisian breed of cattle. The standard deviations between groups in the proportion of males was estimated to be 1.5%. Significant correlations between sire and son and between half-sibs in the sex ratio of their progeny suggest that the differences may have a genetic basis.     

Interactions between SRY and SOX genes in mammalian sex determination

The SRY gene on the mammalian Y chromosome undoubtedly acts to determine testis, but it is still quite unclear how. It was originally supposed that SRY acts directly to activate other genes in the testis-determining pathway. This paper presents an alternative hypothesis that SRY functions indirectly, by interacting with related genes SOX3 (from which SRY evolved) and SOX9 (which appears to be intimately involved in vertebrate gonad differentiation). Specifically, I propose that in females SOX3 inhibits SOX9 function, but in males, SRY inhibits SOX3 and permits SOX9 to enact its testis-determining role. This hypothesis makes testable predictions of the phenotypes of XX and XY individuals with deficiencies or overproduction of any of the three genes, and is able to account for the difficult cases of XX(SRY−) males and transdifferentiation in the absence of SRY. The hypothesis also suggests a way that the dominant SRY sex-determining system of present-day mammals may have evolved from an ancient system relying on SOX3 dosage. BioEssays 20 :264–269, 1998. © 1998 John Wiley & Sons, Inc.     

HLA gene and haplotype frequencies in galicia (NW Spain)

The genetic structure of six populations of Iran (Turks, Kurds, Lurs, Zabolis, Baluchis and Zoroastrians) was examined using data on blood groups, serum proteins and cell enzymes. Our results show conclusively that there are genetic differences among the six populations and the analysis of superimposed R and S matrices defined by Harpending & Jenkins (1973) show that the dispersion of some of the alleles correspond to the dispersion of the populations. The F_ST estimates are not large enough to favour selection on any of the loci studied. The F_IT and F_IS estimates are positive and moderately high suggesting that the genetic differentiation to some extent is influenced by inbreeding.     

HLA-A,B, C gene and haplotype frequencies in Vienna

Summary The HLA-A, B, C haplotype frequencies determined through family investigations in 500 unrelated individuals of the Viennese population were calculated, as well as the gene frequencies of 37 HLA determinants and the linkage disequilibria between the three HLA SD loci (HLA-A, HLA-B, and HLA-C). The existence of HLA-A, B, C superhaplotypes could be confirmed.National Blood Group Reference Laboratory (WHO) and National Tissue Typing Reference Laboratory (Council of Europe)     

Beta-globin gene cluster haplotype frequencies in Khalkhs and Buryats of Mongolia

Beta-globin gene cluster haplotype frequencies of 169 Khalkhs and 145 Buryats were estimated, and their characteristics were compared with those of Evenkis, Oroqens, Koreans, Japanese, and three Colombian Amerindian groups. The present study suggests that Colombian Amerindians diverged first from Asian populations and then Buryats diverged from other Asian populations.