OCR GCSE Biology: Genes, Inheritance and Selection

A species of small lizard lives on a rocky island. The rocks are pale grey, and hunting birds catch the lizards by sight. Most lizards in the population are dark brown, but a few are pale grey. The pale-grey colour is caused by a mutation in one of the lizards' genes.

Over many generations, the proportion of pale-grey lizards in the population increases until almost all the lizards are pale grey.

Explain how the population of lizards changed from mostly dark brown to mostly pale grey by the process of natural selection. In your answer you should refer to variation, mutation, survival and inheritance. (6 marks)

In a breed of cattle, coat colour is controlled by a single gene. The allele for a red coat (R) is dominant to the allele for a white coat (r).

A farmer crosses a bull that is heterozygous for coat colour with a cow that is also heterozygous for coat colour.

(a) Complete a Punnett square for this cross to show the genotypes of the possible offspring. (2 marks)

(b) State the expected ratio of red-coated to white-coated calves, and give the probability, as a percentage, that any one calf will have a white coat. (2 marks)

In humans, biological sex is determined by a pair of sex chromosomes. Females are XX and males are XY.

(a) Using a genetic diagram or a Punnett square, show why approximately half of all babies are expected to be male and half female. (2 marks)

(b) State the probability, as a fraction, that a couple's next child will be a girl. (1 mark)

A hospital lab grows a population of bacteria on a nutrient plate and adds an antibiotic. Almost all the bacteria are killed, but a few survive and grow into new colonies. Over several years, doctors notice that this antibiotic becomes less and less effective at treating infections caused by these bacteria.

(a) Explain how a population of antibiotic-resistant bacteria develops by natural selection. (2 marks)

(b) Suggest one way doctors can help to slow down the development of antibiotic-resistant bacteria. (1 mark)

Scientists have genetically engineered a type of crop plant by inserting a gene from a bacterium. The gene makes the plant produce a substance that is toxic to insect pests, so the crop needs less chemical pesticide.

(a) Describe, in outline, what is meant by genetic engineering. (1 mark)

(b) Suggest one possible concern or disadvantage of growing genetically engineered crops like this. (1 mark)

Charles Darwin published his theory of evolution by natural selection in 1859, but many people did not accept it at the time.

Suggest one reason why Darwin's theory was not widely accepted when it was first published. (1 mark)