AP Syllabus focus:
‘The same genotype can produce multiple phenotypes when environmental conditions alter patterns of gene expression.’
Phenotypic plasticity explains why organisms with identical DNA can look and function differently across environments. In AP Biology, the emphasis is on how external conditions regulate gene expression to generate alternative phenotypes without changing genotype.
Core Concept: Environment-Responsive Phenotypes
Phenotype can shift when environmental cues modify which genes are turned on/off, when they are expressed, and how much product is made. This produces variation within a genotype and can occur during development or throughout life.
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Practice Questions
FAQ
They use designs that control genotype, such as clones or inbred lines, and vary only environment.
They also use “common garden” approaches where different genotypes are raised together to separate genetic from environmental effects.
Some environmentally induced epigenetic states can persist through cell divisions and, more rarely, be transmitted to offspring.
This is typically limited and depends on whether epigenetic marks escape reprogramming during gamete formation and early development.
Limits come from physiology and regulation:
finite ranges of enzyme activity and membrane function
developmental constraints (once structures form, they may not be changeable)
energetic and time costs of sensing and responding
No. If environmental cues are unreliable, plastic responses can produce mismatched phenotypes.
There can also be trade-offs: a phenotype improving performance in one condition may reduce performance in another.
Researchers often use reaction norms: graphs of phenotype versus environment for a genotype.
Differences in slope or shape indicate how strongly and in what pattern gene expression outputs respond to environmental change.
