6 min readConcept sheet1-mark MCQ and assertion-reason; 2-mark questions on variation and inherited traits

Variation and inherited traits

Each generation passes on a common body design with small changes. Sexual reproduction creates more variation than asexual reproduction, and traits like earlobe type are inherited from parents.

HeredityThe passing of traits from parents to offspring

TraitA feature, such as height, eye colour or earlobe type

Sources of variationErrors in DNA copying, plus mixing of DNA in sexual reproduction

EarlobesFree or attached: two forms of one inherited trait

How variation builds up

Offspring get the basic body design from their parents, along with small changes. In asexual reproduction, the changes come only from small errors in DNA copying, so the offspring are very similar to each other. In sexual reproduction, DNA from two parents is mixed, so much more variation appears. When the new individuals reproduce in turn, they pass on their own differences and add new ones, so variety builds up over the generations.

Draw it: variation building up over generations

Even with asexual reproduction, small differences add up. Sexual reproduction adds far more, because DNA from two parents mixes.

Variation in asexual vs sexual reproduction

Asexual reproductionOne parent. Very little variation, only from DNA copying errors. Offspring are almost copies of the parent.

Sexual reproductionTwo parents. Much more variation, from DNA copying errors and the mixing of two parents' DNA.

Activity: observing an inherited trait (earlobes)

1
Look closely at the ears of your classmates.
2
Note whether the lowest part of the ear hangs loose below its joint with the head (free earlobe) or is joined to the side of the head (attached earlobe).
3
Count how many students have each type and work out the percentage of each in the class.
4
Ask each student whether their earlobes match those of their parents.
5★
Conclusion: earlobe type is an inherited trait; free and attached are two variations of the same trait.

★ key step

In real life

In a family photo, a girl may have her mother's curly hair and her father's eye colour: both are inherited traits. Yet no two brothers or sisters, except identical twins, are exactly alike, because of variation.

Exam angle

2 marks: “Why does sexual reproduction produce more variation than asexual reproduction?” Asexual reproduction gives variation only through small DNA copying errors. Sexual reproduction also mixes the DNA of two parents, giving new combinations.

2 marks: “What is meant by an inherited trait? Give two examples.” A feature passed on from parents to offspring through DNA, e.g. free or attached earlobes, eye colour.

Remember it

Asexual reproduction photocopies DNA with tiny errors; sexual reproduction shuffles two parents' DNA. More shuffling, more variety.