Chromosomes, Genes, Alleles, Genotype and Phenotype
This lesson connects the physical organization of DNA with inherited traits. It explains how genetic information is stored, how alternative gene forms arise, and why an organism’s observable features are not the same thing as its allele combination.
Learning goals
- define the central terms precisely
- connect molecular, organismal and population evidence
- apply the ideas to unfamiliar biological cases
Core concepts
A chromosome is one long DNA molecule packaged with proteins and carrying many genes.
A gene is a DNA sequence that contributes to a functional product or influences a biological trait.
A locus is the specific physical position of a gene or DNA marker on a chromosome.
An allele is one of two or more alternative DNA versions found at the same gene locus.
A genotype is the allele combination an organism carries for one gene or a defined set of genes.
A phenotype is an observable or measurable feature produced through interaction between genotype and environment.
Concept map
Why these ideas matter
These concepts help scientists interpret evidence, design fair tests, communicate uncertainty, and make responsible decisions in research, health, agriculture, and environmental management.