Mark scheme: AQA accepts genetic diagrams OR Punnett squares for up to 2 marks
Exam questions — 5 questions · 7 marks
1 markDominant alleleAQA Jun 2024 P2 Q6.1
What is a dominant allele?
A An allele that is only expressed when two copies are present
B An allele that is always expressed, even when only one copy is present
C An allele that codes for a more common characteristic
D An allele that is always passed on to offspring
1 markGenotype/phenotypeAQA 8461 style
A plant has the genotype Tt, where T = tall and t = dwarf. What is its phenotype?
A Tall — because T is dominant over t
B Dwarf — because t is present
C Medium height — because one of each allele is present
D Cannot be determined without more information
3 marksPunnett squareAQA Jun 2024 P2 Q6.3
Polydactyly (extra fingers) is caused by a dominant allele D. A person with genotype Dd has a child with a person with genotype dd. Draw a Punnett square and give the probability that the child will have polydactyly. (3 marks)
+30 XP
1 markTerminologyAQA 8461 style
An organism with the genotype BB is described as:
A Heterozygous
B Homozygous dominant
C Homozygous recessive
D Carrier
2 marksInheritance predictionAQA Jun 2024 P2 Q6.2 style
A person has polydactyly. Their parent also has polydactyly. Explain how you can tell that person 1 (the parent) must be heterozygous (Dd) rather than homozygous dominant (DD). (2 marks)