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Pioneers Science

Science · Cells & organisms

DNA & inheritance

How traits pass from parents to offspring.

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What is DNA?

DNA is a chemical instruction manual inside nearly every cell. It contains genes, which are coded instructions for traits. Traits are features like eye colour, height, or blood type. DNA is passed from parents to offspring during reproduction.

Inheriting traits from parents

Offspring receive half their DNA from each parent. This is why you might have your dad's nose and your mum's hair colour. Each parent passes on one copy of each gene. The combination produces your unique set of traits.

Dominant and recessive genes

Some genes are dominant and some are recessive. Dominant genes show their trait even with just one copy. Recessive genes need two copies to show. For example, brown eyes are usually dominant over blue eyes.

Variation in offspring

Because genes mix differently each time, brothers and sisters are not identical. Random gene combinations create variation. This explains why siblings look similar but not exactly the same. Identical twins share all their DNA, so they look alike.

Worked examples

  1. 1. A mother has brown eyes (dominant) and a father has blue eyes (recessive). Why might their child have brown eyes?

    1. The child receives one eye-colour gene from each parent.
    2. The mother passes a brown-eye gene; the father passes a blue-eye gene.
    3. Brown is dominant, so it shows even with just one copy.
    4. The child has brown eyes because the dominant gene is present.

  2. 2. Two parents both have the ability to roll their tongues. Their child cannot roll their tongue. How is this possible?

    1. Tongue-rolling is a dominant trait; not rolling is recessive.
    2. Each parent must carry one dominant and one recessive gene.
    3. Both parents can roll their tongues because they have one dominant gene each.
    4. Their child inherited the recessive gene from both parents, so cannot roll their tongue.

  3. 3. Why do identical twins look more alike than non-identical twins?

    1. Identical twins form when one fertilised egg splits into two embryos.
    2. They share 100% of their DNA because they came from the same egg and sperm.
    3. Non-identical twins form from two separate eggs fertilised by two separate sperm.
    4. Non-identical twins share only about 50% of their DNA, like regular siblings.

Try it yourself

A plant has red flowers (dominant) and white flowers (recessive). If a plant inherits one red gene and one white gene, what colour will its flowers be?

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