A-LevelBiologyInherited change9700/42 · Oct/Nov 2025 · Q28 Marks
Explain the terms gene, genotype and phenotype. gene genotype phenotype
- (a)Explain the terms gene, genotype and phenotype. gene genotype phenotype[3]
- (b)A monohybrid genetic cross can be carried out to produce an F1 and an F2 generation. • Outline how a monohybrid genetic cross is carried out. • State the expected percentage of each of the different offspring genotypes in the F2 generation. Assume that the inheritance pattern is for autosomal dominant and recessive alleles.[5]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.
- [3] (a) gene a section of DNA / sequence of (DNA) bases, coding for a (specific) polypeptide ; genotype all the alleles / alleles in an organism / (two) alleles of one gene ; phenotype (observable) features / characteristics / traits / appearance, (of an organism);
- [5] (b) any four from: 1 mate / breed / cross, homozygous (parents); 2 dominant (parent) with recessive (parent); 3 to produce the F1, offspring / generation ; 4 (F1) offspring are heterozygotes ; 5 mate / breed / cross, F1 offspring / F1 generation / heterozygotes or self an F1 offspring (plant); 6 to produce the F2, offspring / generation ; plus 7 25% (F2) offspring are, homozygous dominant, / AA and 50% are, heterozygotes / Aa and 25% are, homozygous recessive / aa ; A a ratio e.g. AA : Aa : aa 1 : 2 : 1
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