Edexcel GCSE Combined Science: Biology: Genetics, Variation and Evolution
6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
A species of beetle lives on a tree trunk. Most beetles are pale brown, but a few are dark. Birds hunt the beetles by sight. When pollution darkens the tree bark, the population over several generations becomes mostly dark.
Explain, using the theory of evolution by natural selection, how the beetle population came to be mostly dark. (6 marks)
In a species of mouse, fur colour is controlled by a single gene. The allele for brown fur (B) is dominant to the allele for white fur (b).
A heterozygous brown mouse (Bb) is crossed with a white mouse (bb).
(a) Complete a Punnett square for this cross and use it to give the genotypes of the offspring. (2 marks)
(b) State the expected ratio of brown to white offspring, and give this as a percentage chance that any one offspring is white. (2 marks)
Sexual and asexual reproduction both occur in living organisms.
(a) State one way in which the offspring produced by asexual reproduction differ from those produced by sexual reproduction, in terms of their genes. (1 mark)
(b) Give one advantage to a plant of being able to reproduce asexually. (1 mark)
(c) Name the type of cell division that produces gametes for sexual reproduction. (1 mark)
A family pedigree shows the inheritance of a condition caused by a recessive allele (a). The dominant allele (A) gives the unaffected phenotype.
The information from the pedigree is summarised in the table below.
| Family member | Phenotype |
|---|---|
| Grandfather (generation 1) | Affected |
| Grandmother (generation 1) | Unaffected |
| Mother (generation 2, their daughter) | Unaffected |
| Father (generation 2, married in) | Unaffected |
| Child (generation 3) | Affected |
(a) State the genotype of the affected grandfather, and explain how you know. (2 marks)
(b) The child in generation 3 is affected, but both of the child's parents are unaffected. Explain what this tells you about the genotype of the mother and father. (1 mark)
Some bacteria have become resistant to an antibiotic. Doctors are advised to finish a full course of antibiotics and not to use them for minor infections.
Explain how the over-use of antibiotics can lead to the spread of antibiotic-resistant bacteria. (2 marks)
DNA is found in the nucleus of cells and carries the genetic code.
Name the shape of a DNA molecule. (1 mark)