Packaging inherited information

By UK GCSE Biology · independent study · myAudience

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Packaging inherited information

Chromosomes are long DNA molecules associated with proteins. A gene is a region of DNA carrying information used to make a functional product, often a protein. One chromosome contains many genes; a gene and a chromosome are different scales of organization.

Distinguish levels of organization: a gene is a region of DNA, a chromosome packages a large DNA molecule, and the genome is the organism’s full genetic information. Drawing a chromosome as an X represents a replicated stage; it does not mean chromosomes permanently have that shape. Label the stage and model before interpreting a diagram.

Chromosomes normally occur in pairs in the human body-cell model, with one inherited member of each pair from each parent. A chromosome carries many genes; paired chromosomes can carry different versions of a gene. An X-shaped drawing represents a chromosome after its DNA has been copied, when two sister copies remain attached. It is not the permanent shape of every chromosome throughout the cell cycle.

Worked example: Is “one chromosome equals one gene” a useful model?

A chromosome contains a long DNA molecule

Many separate gene regions occur along it

Answer: No; one chromosome carries many genes.

Check your understanding: What is an allele?

Answer: A version of a gene.

Why: Alleles occupy corresponding gene positions and can differ in their DNA sequence.