Concept 2: Genes are stable, passed on in sex cells and control traits

We now know that genes are segments of DNA, the deoxyribonucleic acid molecule that makes up chromosomes (Fig. 3 & 4). DNA is a stable molecule and therefore genes are stable. They maintain their structural integrity as they are copied and passed on from cell to cell (for somatic cells) and from generation to generation (for gamete cells). Because they maintain their structure, genes can reliably encode genetic information, instruct the cell how to make specific proteins, and ultimately control traits or characteristics in the organism. Geneticists use the term phenotype to designate the trait or combination of traits observed in an individual (Fig. 5).

Figure 3. DNA, deoxyribonucleic acid, has subunits that code information and assemble into a stable double helix structure. (Image by P. Hain)

Figure 4. A chromosome is a long DNA molecule and contains many genes, each with it’s own coded information. (Image by P. Hain)

Figure 5. The coded information in genes instructs the cell to make proteins that control specific traits or phenotypes such as the color of cells and tissues. (Image by P. Hain)