AP Syllabus focus:
‘Human height and weight illustrate how nutrition, activity, and other environmental factors modify phenotypes without changing genotype.’
Human traits often reflect both inherited potential and lived experience. Height and weight are especially useful for understanding how environmental conditions shape phenotype through physiology and gene expression, without altering DNA sequence.
Core idea: environment changes phenotype, not genotype
Height and weight as multifactorial traits
Height and body mass are influenced by many genes (polygenic) and many environmental variables.
An individual’s genotype helps set a range of possible outcomes, but the observed phenotype depends on conditions during development and across life.
Environmental effects can be:
Practice Questions
FAQ
They use designs such as twin studies, adoption studies, and large cohort analyses.
Comparisons of identical vs non-identical twins help estimate relative contributions while recognising environments can still differ.
Yes.
Changes in glycogen storage, hydration, gut contents, and hormonal signalling can shift body mass rapidly, while DNA sequence remains unchanged.
Diet and medications can alter microbial communities.
Microbes can influence energy extraction from food, inflammation, and metabolites that affect appetite and insulin sensitivity.
They can affect chronic stress, sleep, food quality, exposure to pollutants, and infection rates.
These inputs can shift endocrine signalling and long-term metabolic regulation.
Some can.
Early-life conditions may leave stable methylation or chromatin patterns in certain tissues, influencing later appetite regulation, insulin signalling, or fat storage tendencies.
