Final answer:
Genetic markers account for less than 2% of the variability in individual weight and BMI, with most variation attributed to non-genetic factors.
Step-by-step explanation:
Genetic markers explain less than 2% of the variation in individual weight and BMI. Genetic markers are essential elements in constructing genetic maps. Just as a road map requires landmarks such as rivers and mountains, the generation of genetic maps relies on the use of genetic markers, which have significantly evolved from known genes to more sophisticated markers including those based on non-coding DNA. These minor differences in the genome between individuals are instrumental for genetic mapping, as a good genetic marker shows variability or polymorphism within the population. When it comes to analyzing characteristics like weight and BMI, most variation is due to non-genetic factors; therefore, the heritability fraction for these traits is relatively low, underscoring that genetics play a minor role compared to environmental and lifestyle factors.