OCR A LEVEL BIOLOGY EXAM STUDY
GUIDE 2026 PRACTICE MATERIALS
●● General possible effects of gene mutations. Answer: Beneficial,
neutral, harmful
●● Gene mutation. Answer: Changes to the sequence of bases
●● Mutation. Answer: Changes to the amount or arrangement of genetic
material
●● Type of mutation that insertion and deletion mutations cause.
Answer: Frameshift mutations
●● Examples of positive effects as a result of mutations. Answer: Ability
to digest lactose, immunity to HIV, resistance to malaria
●● Mutation responsible for immunity to HIV. Answer: Deletion which
changes the receptor molecules' shape
●● Mutation responsible for resistance to malaria. Answer: Substitution
which causes heterozygosity for sickle cell anaemia
, ●● Examples of negative effects as a result of mutations. Answer: Cystic
fibrosis, phenylketonuria, sickle cell anaemia
●● Mutation responsible for cystic fibrosis. Answer: Deletion of one
amino acid
●● Mutation responsible for phenylketonuria. Answer: Substitution
●● Mutation responsible for sickle cell anaemia. Answer: Substitution
●● Physical mutagens. Answer: Ionising radiation
●● Chemical mutagens. Answer: Deaminating agents
●● Biological agents. Answer: Alkylating agents, base analogs, viruses
●● How does ionising radiation lead to mutations?. Answer: Break one
or both DNA strands
●● How do deaminating agents lead to mutations?. Answer: Switch
between bases, switching between cytosine and uracil
GUIDE 2026 PRACTICE MATERIALS
●● General possible effects of gene mutations. Answer: Beneficial,
neutral, harmful
●● Gene mutation. Answer: Changes to the sequence of bases
●● Mutation. Answer: Changes to the amount or arrangement of genetic
material
●● Type of mutation that insertion and deletion mutations cause.
Answer: Frameshift mutations
●● Examples of positive effects as a result of mutations. Answer: Ability
to digest lactose, immunity to HIV, resistance to malaria
●● Mutation responsible for immunity to HIV. Answer: Deletion which
changes the receptor molecules' shape
●● Mutation responsible for resistance to malaria. Answer: Substitution
which causes heterozygosity for sickle cell anaemia
, ●● Examples of negative effects as a result of mutations. Answer: Cystic
fibrosis, phenylketonuria, sickle cell anaemia
●● Mutation responsible for cystic fibrosis. Answer: Deletion of one
amino acid
●● Mutation responsible for phenylketonuria. Answer: Substitution
●● Mutation responsible for sickle cell anaemia. Answer: Substitution
●● Physical mutagens. Answer: Ionising radiation
●● Chemical mutagens. Answer: Deaminating agents
●● Biological agents. Answer: Alkylating agents, base analogs, viruses
●● How does ionising radiation lead to mutations?. Answer: Break one
or both DNA strands
●● How do deaminating agents lead to mutations?. Answer: Switch
between bases, switching between cytosine and uracil
