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Changes posed to the fetus through ethanol exposure may significantly effect growth and development; these are collectively known as fetal alcohol spectrum disorders (FASD). [20] The exact interaction between ethanol and the developing fetus is complex and largely uncertain, however, several direct and indirect effects have been observed as the ...
Like many other medical conditions, obesity is the result of an interplay between environmental and genetic factors. [2] [3] Studies have identified variants in several genes that may contribute to weight gain and body fat distribution, although only in a few cases are genes the primary cause of obesity. [4] [5]
The step lengthens as the pregnancy progresses, due to weight gain and changes in posture. On average, a woman's foot can grow by a half size or more during pregnancy. In addition, the increased body weight of pregnancy, fluid retention, and weight gain lowers the arches of the foot, further adding to the foot's length and width.
The changes that constitute acquired characteristics can have many manifestations and degrees of visibility, but they all have one thing in common. They change a facet of a living organism's function or structure after birth. For example: The muscles acquired by a bodybuilder through physical training and diet. The loss of a limb due to an injury.
Genetic load may increase when deleterious mutations, migration, inbreeding, or outcrossing lower mean fitness. Genetic load may also increase when beneficial mutations increase the maximum fitness against which other mutations are compared; this is known as the substitutional load or cost of selection.
Population genetics is the branch of evolutionary biology responsible for investigating processes that cause changes in allele and genotype frequencies in populations based upon Mendelian inheritance. [3] Four different forces can influence the frequencies: natural selection, mutation, gene flow (migration), and genetic drift. A population can ...
Childhood obesity is often the result of an interplay between many genetic and environmental factors. Polymorphisms in various genes controlling appetite and metabolism predispose individuals to obesity when sufficient calories are present. Over 200 genes affect weight by determining activity level, food preferences, body type, and metabolism. [36]
Set point theory does not on its own explain why body mass index for humans, measured as a proxy for fat, tends to change with increasing age or why obesity levels in a population vary depending on socioeconomic or environmental factors (or why weight tends to change for an individual when socioeconomic status and environment change). [4]