Genetics

Inheritance, meiosis, genetic linkage, and population genetics

What is genetics?

Genetics is the study of heredity — how traits are passed from parents to offspring, and how variations in genes produce the wide range of differences seen between individuals of the same species.

Genes and chromosomes

A gene is a specific segment of DNA (covered in the Molecular Biology article) that contains the instructions for a particular trait or function. Genes are organized along chromosomes, long, tightly coiled strands of DNA found inside the cell nucleus. Most organisms, including humans, inherit one full set of chromosomes from each parent, giving them two copies of most genes.

Dominant and recessive traits

For many genes, the two inherited copies (called alleles) can differ slightly, and this can affect which trait actually appears. A dominant allele will produce its trait even if only one copy is present; a recessive allele only produces its trait if both inherited copies are the recessive version. This basic pattern, first worked out by Gregor Mendel through careful pea plant breeding experiments in the 1860s, explains many simple inheritance patterns still used as a teaching foundation today.

How traits actually get passed down

During reproduction, each parent passes on exactly one of their two copies of each gene to their offspring, chosen essentially at random from their own two copies. This is why siblings, while sharing the same parents, don't have identical genetic makeups (unless they're identical twins) — each inherits a different random combination of alleles from each parent.

Why genetics matters

Genetics explains why certain traits and health conditions run in families, underlies modern genetic testing and counseling, guides the breeding of crops and livestock with desirable traits, and provides the foundation for understanding evolution, covered further in the Ecology article.