So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

http://drop-kicker.com/wp-content/uploads/2014/01/kyle-bia.pdf

Bioelectrical impedance analysis--part I: review of principles and methods.

We employed a whole body magnetic resonance imaging protocol to examine the influence of age, gender, body weight, and height on skeletal muscle (SM) mass and distribution in a large and heterogene...

Skeletal muscle mass and distribution in 468 men and women aged 18–88 yr

BACKGROUND: The loss of muscle mass is considered to be a major determinant of strength loss in aging. However, large-scale longitudinal studies examining the association between the loss of mass and strength in older adults are lacking. METHODS: Three-year changes in muscle mass and strength were determined in 1880 older adults in the Health, Aging and Body Composition Study. Knee extensor strength was measured by isokinetic dynamometry. Whole body and appendicular lean and fat mass were assessed by dual-energy x-ray absorptiometry and computed tomography. RESULTS: Both men and women lost strength, with men losing almost twice as much strength as women. Blacks lost about 28% more strength than did whites. Annualized rates of leg strength decline (3.4% in white men, 4.1% in black men, 2.6% in white women, and 3.0% in black women) were about three times greater than the rates of loss of leg lean mass ( approximately 1% per year). The loss of lean mass, as well as higher baseline strength, lower baseline leg lean mass, and older age, was independently associated with strength decline in both men and women. However, gain of lean mass was not accompanied by strength maintenance or gain (ss coefficients; men, -0.48 +/- 4.61, p =.92, women, -1.68 +/- 3.57, p =.64). CONCLUSIONS: Although the loss of muscle mass is associated with the decline in strength in older adults, this strength decline is much more rapid than the concomitant loss of muscle mass, suggesting a decline in muscle quality. Moreover, maintaining or gaining muscle mass does not prevent aging-associated declines in muscle strength.

/pdf/the-loss-of-skeletal-muscle-strength-mass-and-quality-in-2n0xezhry5.pdf

The Loss of Skeletal Muscle Strength, Mass, and Quality in Older Adults: The Health, Aging and Body Composition Study

The saimie paper suggests how susceptible individuals could reduce their total intake of aluminium. In presenting the cpidemiological evidence for a link betveen aluminium and Alzheimcr's, Nart'n suggests that although definite proof is still lacking, there is more than enough positixe evidence to fuel further epidemiological investigation. It states that such investigations might specificallx address the issue of the confounding cffect of silicon and an assessment of exposure to spccific

https://jech.bmj.com/content/jech/47/6/511.4.full.pdf

Methodology for Genetic Studies of Twins and Families

Context.—Hydroxycitric acid, the active ingredient in the herbal compound Garcinia cambogia, competitively inhibits the extramitochondrial
enzyme adenosine triphosphate–citrate (pro-3S)-lyase. As a citrate cleavage
enzyme that may play an essential role in de novo lipogenesis inhibition, G cambogia is claimed to lower body weight and reduce fat
mass in humans.Objective.—To evaluate the efficacy of G cambogia for
body weight and fat mass loss in overweight human subjects.Design.—Twelve-week randomized, double-blind, placebo-controlled trial.Setting.—Outpatient weight control research unit.Participants.—Overweight men and women subjects (mean body mass index [weight in kilograms
divided by the square of height in meters], approximately 32 kg/m2).Intervention.—Subjects were randomized to receive either active herbal compound (1500
mg of hydroxycitric acid per day) or placebo, and both groups were prescribed
a high-fiber, low-energy diet. The treatment period was 12 weeks. Body weight
was evaluated every other week and fat mass was measured at weeks 0 and 12.Main Outcome Measures.—Body weight change and fat mass change.Results.—A total of 135 subjects were randomized to either active hydroxycitric
acid (n=66) or placebo (n=69); 42 (64%) in the active hydroxycitric acid group
and 42 (61%) in the placebo group completed 12 weeks of treatment (P=.74). Patients in both groups lost a significant amount of weight
during the 12-week treatment period (P<.001);
however, between-group weight loss differences were not statistically significant
(mean [SD], 3.2 [3.3] kg vs 4.1 [3.9] kg; P=.14).
There were no significant differences in estimated percentage of body fat
mass loss between treatment groups, and the fraction of subject weight loss
as fat was not influenced by treatment group.Conclusions.—Garcinia cambogia failed to produce significant
weight loss and fat mass loss beyond that observed with placebo.

https://jamanetwork.com/journals/jama/articlepdf/188147/JOC80747.pdf

Garcinia cambogia (Hydroxycitric Acid) as a Potential Antiobesity Agent A Randomized Controlled Trial

Conventional single frequency bioimpedance analysis (BIA) systems require technician placement of arm and leg gel electrodes, a suitable location for recumbent measurements, and a separate measurement of body weight. The aim of this study was to evaluate a new single frequency 50 kHz leg-to-

Bioimpedance analysis: evaluation of leg-to-leg system based on pressure contact foot-pad electrodes

Objectives: Air displacement plethysmography (ADP) may provide a partial alternative to body density (Bd) and therefore body composition measurement compared to conventional hydrodensitometry (Hd) in children. As there are no evaluation studies of ADP in children, this study had a two-fold objective: to compare Bd estimates by ADP and Hd; and to compare fat estimates by both ADP and Hd to fat estimates by another reference method, dual energy X-ray absorptiometry (DXA). Setting: Obesity Research Center, St. Luke’s=Roosevelt Hospital, New York, USA. Subjects: One hundred and twenty subjects (66 females=54 males) who ranged in age from 6 ‐ 86 y and in body mass index (BMI, kg=m 2 ) from 14.1 ‐ 40.0 kg=m 2 met study entry criteria. Study Design: Cross-sectional study of healthy children (age 19 y) and adult group for comparison to earlier studies. Each subject completed ADP, Hd, and DXA studies on the same day. Only subjects with subjectivelyjudged successful Hd studies were entered into the study cohort. Results: There was a high correlation between Bd by ADP and Hd (Bd Hda 0.11a 0.8966Bd ADP; ra 0.93, SEEa 0.008 g=cm 3 , P 0.9, P< 0.0001) with %fat by DXA in child and adult subgroups. Bland ‐ Altman analyses revealed no significant %fat bias by either ADP or Hd vs DXA in either children or adults, although a bias trend (Pa 0.11) was detected in the child subgroup. Conclusion: With additional refinements, the air displacement plethysmography system has the potential of providing an accurate and practical method of quantifying body fat in children as it now does in adults. Sponsorship: This study was in-part supported by NIH Grants RR00645, NIDDK 42618 and NIDDK 37352. Descriptors: air displacement plethysmography; body composition; hydrodensitometry; children

Body composition in children and adults by air displacement plethysmography.

Objective. Insight into genetic and environmental influences on fat mass, independent of body mass index (BMI; kg/m 2 ), is expected to enhance methods for treating pediatric obesity. However, few studies have estimated the heritability of fat mass in pediatric samples, and those conducted have relied primarily on BMI measurements. Present Study. Using bioimpedance analysis, the present study tested a series of hypotheses predicting significant genetic and environmental influences on percent body fat (PBF) above and beyond BMI. Subjects were 66 pairs of twins, including 41 monozygotic and 25 dizygotic pairs, from 3 to 17 years of age. Structural equation modeling tested hypotheses, adjusting for demographic variables. Results. Analyses indicated significant genetic influences on PBF, with genes estimated to account for 75% to 80% of the phenotypic variation. The remaining variation was attributable to nonshared environmental influences. Multivariate analyses revealed sizable genetic correlations and environmental correlations between BMI and PBF (r g =.74 and r e =.67, respectively), suggesting that some genes and environmental experiences influence both phenotypes. However, analyses confirmed genetic and environmental influences on PBF above and beyond BMI. For example, 62.5% of the total genetic variation in PBF was attributable to genes that influenced PBF but not BMI. Conclusion. There seems to be a substantial genetic contribution to fat mass distinct from BMI in a sample of children and adolescents. Studies testing putative genetic or environmental determinants of pediatric obesity might be strengthened further by including research-based body composition methods. Pediatrics 1999;104: 61-67; pediatric obesity, twin design, heritability, nonshared environment, bioimpedance analysis, body mass index, body composition.

Evidence for Independent Genetic Influences on Fat Mass and Body Mass Index in a Pediatric Twin Sample

Despite skeletal muscle's central role in the pathogenesis of sarcopenia, measurement methods remain underinvestigated and inadequately validated. Our review indicates that skeletal muscle (SM) measurement methods quantify different components and properties of muscle, ranging from the atomic to whole-body levels of body composition. Laboratory methods tend to measure whole body SM (e.g., total muscle protein, muscle cell mass, and adipose tissue-free SM components) while epidemiological methods tend to measure regional muscle (e.g., anatomic SM of an extremity). Advances in computerized axial tomography and magnetic resonance imaging methods now allow accurate estimates of whole body and regional SM and promise to finally permit comprehensive in vivo studies of SM biology and methodology. These imaging methods may help to resolve many of the confusing issues that surround the investigation of this major body composition component.

Christopher Nuñez

Papers

Garcinia cambogia (Hydroxycitric Acid) as a Potential Antiobesity Agent A Randomized Controlled Trial

Bioimpedance analysis: evaluation of leg-to-leg system based on pressure contact foot-pad electrodes

Body composition in children and adults by air displacement plethysmography.

Evidence for Independent Genetic Influences on Fat Mass and Body Mass Index in a Pediatric Twin Sample

Measurement of Skeletal Muscle: Laboratory and Epidemiological Methods