Advantages of sexual reproduction: • produces variation in the offspring •…

The idea

Sexual reproduction combines genetic material from two parents, so offspring differ from each other and from their parents. This variation matters when the environment changes: individuals with alleles suited to the new conditions are more likely to survive and reproduce, so those alleles become more common in the population by natural selection. A population with little variation may be wiped out by a new disease or climate shift, whereas a varied population is more likely to contain some survivors. Humans can exploit this process in selective breeding: by choosing parents with desirable characteristics, such as high yield or disease resistance, breeders change the population faster than natural selection alone, helping to increase food production from crops and livestock.

What earns the marks

• Sexual reproduction produces offspring that are genetically different from each other and from their parents.
• Variation means that, when the environment changes, some individuals may have characteristics giving a survival advantage.
• Those surviving individuals reproduce and pass on the advantageous alleles, so natural selection changes the population over generations.
• Humans can speed up natural selection by selective breeding, choosing parents with desired characteristics.
• Selective breeding of crops and livestock can raise yield or quality, increasing food production.

Common mistakes and how to put them right

• Claiming that variation is always beneficial.

  Put it right: Variation provides the raw material on which natural selection acts, and whether a characteristic helps depends on the environment.

• Saying that organisms choose to adapt or mutate.

  Put it right: Variation arises from genetic differences and selection acts on existing variation.

• Confusing selective breeding with genetic engineering.

  Put it right: Selective breeding chooses existing individuals to breed, whereas genetic engineering transfers genes directly.

Exam tips

• Link each advantage to a consequence: variation leads to survival, survival leads to reproduction, and reproduction passes on advantageous alleles.
• Use a named context, such as a disease affecting a crop, to show how variation gives a survival advantage.
• When discussing selective breeding, state the characteristic being selected and how it increases food production.