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At least 469 records · Page 26Linked to original sources
PubMed1980

Nursing frequency, gonadal function, and birth spacing among !Kung hunter-gatherers.

Mothers among !Kung hunter-gatherers nurse briefly and frequently, with brief intervals between nursing bouts (mean +/- standard error, 13.19 +/- 1.28 minutes). The low levels of 17 beta-estradiol and progesterone in the serum of the mother are correlated with infant's age and with interbout interval, but not with total nursing time. Maternal gonadal function is apparently suppressed by a timing-dependent, prolactin-mediated effect of breast stimulation. Interbout interval may be a key variable in lactation infertility. If so, it solves the puzzle of !Kung birth spacing.

Amenorrhea↗
PubMed1991

Water homeostasis in desert-dwelling horses.

This study set out to investigate tolerance of the body water pool to short-term water deprivation in horses and, in particular, to assess whether feral horses from the Namib Desert showed tolerance to dehydration superior to Transvaal. Hydration status was compared in six feral horses from the Namib Desert and in six Boerperd farm horses under conditions of normal hydration and after 72 h of dehydration. Under normal hydration, the two groups did not differ significantly in water intake, plasma sodium and potassium concentrations, plasma osmolality, hematocrit, total plasma protein, body water content, or water turnover (ml.kg-0.82.day-1). The Namib horses were significantly smaller (P less than 0.0001) and turned over 5 liters less water per day than the Boerperd during normal hydration and 4 liters less during dehydration. Increases in plasma sodium concentration after 72 h of dehydration were greater (P less than 0.05) in the Namib horses. It was concluded that horses can easily tolerate water deprivation that results in a 12% reductions in body mass. The feral horses of the Namib desert were not significantly different per unit mass from domestic horses with regard to indexes of total body water content under conditions of normal hydration and after 72 h of dehydration. Their smaller size and, hence, lower water turnover might be mechanisms they use for survival in the Namib Desert.

Adaptation, Physiological↗
PubMed1983

Sero-genetic studies on the Caucasoids of South West Africa/Namibia.

Gene marker studies on the Afrikaans and German populations of South West Africa/Namibia reveal that both very closely resemble their parent European stocks but that the Germans show appreciable evidence of having received a genetic contribution from non-Caucasoid, probably Khoi or Negro, sources.

Blood Group Antigens↗
PubMed2006

CYP2A6 polymorphism reveals differences in Japan and the existence of a specific variant in Ovambo and Turk populations.

CYP2A6 is a polymorphic enzyme, and CYP2A6 genotype has been shown to be associated with smoking habits and lung cancer. We investigated CYP2A6 polymorphism in Japanese from four different geographic areas of Japan and in the Ovambo and Turk populations. Using two polymerase chain reaction restriction fragment length polymorphisms (PCR-RFLPs), we identified the functionally important variants of CYP2A6: *1A, *1B, *1F, *1G, *4A, and *4D. In the Japanese population the highest frequencies of the CYP2A6*1A allele were observed in subjects from the Fukuoka (Kyushu Island) and Ehime (Shikoku Island) prefectures, whereas subjects in Shimane and Tottori (both located on the Japan Sea side of Honshu Island) showed the highest frequencies of the CYP2A6*1B allele. In the Tottori and Shimane groups no subject was homozygous for the CYP2A6*4A allele, a whole gene deletion type that is prevalent among Asians. In the Ovambo and Turk populations the CYP2A6*1A allele was predominant. Furthermore, two alleles undetected in the Japanese were observed in these latter two ethnic groups: CYP2A6*1G was found solely in the Ovambos, and CYP2A6*1F was found solely in the Turks. The present study is the first to show interprefecture differences in CYP2A6 polymorphism in Japanese who live in relatively close but distinct geographic areas; this is also the first study to evaluate CYP2A6 variations among these Japanese and the Ovambo and Turk populations. The distribution results of these alleles could help to define the true significance of CYP2A6 polymorphism as a genetic susceptibility marker in worldwide populations.

Alleles↗
PubMed2006

Frequency of a single nucleotide (A2317G) and 56-bp variable number of tandem repeat polymorphisms within the deoxyribonuclease I gene in five ethnic populations.

BACKGROUND: The single nucleotide polymorphism (SNP) at deoxyribonuclease I (DNase I), designated as DNASE1 (NCBI SNP number; 1053874), in exon 8 (A2317G) is considered to be one of the susceptibility genes for gastric and colorectal carcinoma and myocardial infarction. Recently, the presence of a variable number of tandem repeat (VNTR) polymorphisms, designated as HumDN1, in intron 4 was found. METHODS: Simultaneous genotyping of the DNASE1 and HumDN1 polymorphisms within the DNase I gene was performed in Ovambo, Turkish, Mongolian, Korean, and Japanese populations. RESULTS: The allele frequencies of the DNASE1 and HumDN1 loci differed among five populations. There was general uniformity for the two polymorphisms in the three Asian populations, but significant differences in genotype distribution between the Ovambo and Turkish populations. The DNASE1 *1 and HumDN1 *3 alleles were found to be the most predominant among the Ovambos. Turks had the highest allele frequency for DNASE1 *2, HumDN1 *4, and HumDN1 *5. A linkage disequilibrium between the single-nucleotide (A2317G) and 56-bp VNTR polymorphisms was revealed in all populations except the Ovambos. CONCLUSIONS: This study is the first to demonstrate the simultaneous genotyping of DNASE1 and HumDN1 polymorphisms and reveal the existence of a certain genetic heterogeneity in the worldwide distribution of these two polymorphisms. The combination of the two polymorphisms within a DNase I gene may be potentially useful for clinical purposes and in population genetic studies.

Asian People↗
PubMed2001

Determining landscape function and ecosystem dynamics: contribution to ecological restoration in the southern Namib desert.

The southern Namib is characterized by high biodiversity, changes in winter and summer rainfall, extreme climatic conditions and associated geomorphologic processes, a paucity of ecological knowledge, and multiple environmental threats posed by conflicting development options. With the long-term view to establish a research initiative focussing on restoration ecology in the southern Namib Desert, this article provides a review of current ecological knowledge and proposes potential research priorities. The aims of a research initiative would be two-fold. On the academic side, understanding processes operating at different scales will be critical to develop methods of ecological restoration suitable for southern Namib ecosystems. On the practical side, the development of appropriate methods will focus on facilitating ecological processes such as restoration of biologically active substrate, natural succession, and concentration of limited resources. The function of landscapes, plant-soil interface, soil-, vegetation- and plant population dynamics will likely provide some of the answers for ecological restoration.

Desert Climate↗
PubMed2001

A study to verify a reported excess of chromosomal aberrations in blood lymphocytes of Namibian uranium miners.

This report describes a study to verify an earlier report of excess chromosomal damage in the blood lymphocytes of uranium miners. Coded blood samples from 10 miners and 10 controls were analyzed conventionally for unstable aberrations and by FISH for translocations. Conventional analysis, scoring 1000 metaphases per subject, showed no significant difference between miners and controls in the frequencies of chromosome- and chromatid-type aberrations. Investigators at two laboratories undertook FISH analyses, each scoring 4000 metaphases per subject. When the data from each laboratory were examined separately, one found slightly more translocations in the miners while the other found fewer. In neither case was the difference significant at the 95% level of confidence. Combining the data likewise showed no significant excess of damage in the miners. This applied to simple one- and two-way translocations and to cells with complex exchanges. There was no correlation between levels of translocations and total lifetime doses from occupational and/or background irradiation. A borderline significant excess of rogue cells was found in the miners. This may be a chance observation, as these rare, highly abnormal cells are considered to be unrelated to radiation exposure and are probably due to a virus. The overall conclusion is that the frequency of chromosomal damage in the miners did not exceed that in the controls. Therefore, the result of the earlier study was not confirmed.

Chromosome Aberrations↗
PubMed1994

The high frequency of the Hb B2 variant in the Herero population: a founder effect?

The beta-globin gene cluster haplotype associated with the delta-globin variant Hb B2 was determined in Herero individuals from six different families, in order to establish whether founder effect was responsible for the high frequency of this variant in the population. The electrophoretic detection of Hb B2 was confirmed at the molecular level by polymerase chain reaction, followed by Cfo I digestion. The haplotype associated with the Hb B2 chromosome was determined in two families, and was shown to be the same. In the remaining four families the haplotypes could not be established conclusively, but were consistent with the haplotype observed in the other two families. The high gene frequency of Hb B2 is thus likely to have resulted form founder effect.

Black People↗