Inheritance — AS & A Level Biology (9700) questions by topic
Explain, deduce and suggest are the command words that dominate here, applied to Punnett squares, dihybrid ratios and gene-to-phenotype reasoning: explaining a 9:3:3:1 ratio through independent assortment, deriving genotypes for a cross involving multiple alleles, and linking a haemophilia allele to its protein and phenotype effect. Explain in particular wants the genetic mechanism named, such as independent assortment at metaphase I, not just the ratio restated.
This set has 25 real questions from 2023 to 2025 papers, worth 1 to 14 marks, so single-genotype recall sits beside multi-part inheritance explanations. Submitting Punnett-square working for instant marking is useful here, since a superscript written the wrong way round, or a genotype given where a phenotype is asked for, is flagged immediately.
What examiners look for
- A 9:3:3:1 ratio is frequently misread as evidence of linkage, when it actually shows two genes assorting independently on separate autosomes.
- The superscript letter for an allele is commonly written in the wrong case, for example 'H' instead of 'h'.
- Punnett squares are sometimes completed with genotypes only, without the corresponding phenotypes being shown.
- A recurring error starts a cross from the original parental genotypes instead of from the F1 individuals actually being crossed.
- Strong answers state that independent assortment happens at metaphase I, and use allele symbols to show how two chromosome pairs can align in different ways to produce the observed phenotype ratio.
May–June 2025, Paper 41
Porphyria is a group of inherited diseases. Three types of porphyria are X-linked protoporphyria, variegate porphyria and congenital erythropoietic porphyria (CEP). Fig. 3.1 shows…
Answer this question and get it marked →May–June 2025, Paper 42
Rice, Oryza sativa, is an important grain crop. A rice grain is a seed and can have a structure known as an awn, which projects from the tip of the grain. The development of awns…
Answer this question and get it marked →Sexual reproduction in plants and animals involves the formation of gametes as a result of meiosis and the process of fertilisation. In most species of plants and animals, the…
Answer this question and get it marked →May–June 2025, Paper 43
Antibiotic resistance in bacteria has increased in recent years. A small polynucleotide drug has been developed to combat this. Some bacteria become antibiotic resistant by…
Answer this question and get it marked →May–June 2025, Paper 44
Some inherited diseases are caused by mutations in genes. Huntington's disease is caused by a mutation in the HTT gene that codes for the huntingtin protein. Using Huntington's…
Answer this question and get it marked →Manx cats are domestic cats that can be either tailless or tailed. A survey of domestic cats in a town found that 6.8% of cats had tails (homozygous recessive, tt). Using the…
Answer this question and get it marked →May–June 2025, Paper 53
Drosophila melanogaster (fruit flies) have many heritable characteristics, including eye colour. Eye colour in Drosophila is determined by two genes, A and B, which are on…
Answer this question and get it marked →May–June 2024, Paper 41
Many different genes are involved in the production of pigments in mammals. One example is the TYR gene. In humans the TYR gene is located on chromosome 11. Fig. 6.1 shows the…
Answer this question and get it marked →May–June 2024, Paper 42
Explain why the inheritance of colour pattern in tortoise beetles can be described as involving multiple alleles.
Answer this question and get it marked →Genes have a role in determining the overall phenotype of an organism. Using haemophilia as an example, explain the relationship between a gene, a protein and a phenotype.
Answer this question and get it marked →May–June 2024, Paper 43
A genetic cross was carried out between two plants heterozygous at both gene loci. The resulting offspring genotypes are shown in a Punnett square in Fig. 3.2 (gametes TD, Td, tD,…
Answer this question and get it marked →October–November 2024, Paper 42
Genetic crosses can be used to investigate patterns of inheritance. A mutation in a gene involved in fruit colour in tomato plants, Solanum lycopersicum, results in the production…
Answer this question and get it marked →October–November 2024, Paper 43
Lunularia cruciata is a primitive plant. Its body consists of a flattened sheet of photosynthetic tissue called a thallus. Fig. 5.1 shows L. cruciata with two different types of…
Answer this question and get it marked →Populations of the moth Biston betularia live in Europe and in North America. The most common phenotype on both continents is a pale wing colour with light-grey shading (the…
Answer this question and get it marked →February–March 2023, Paper 42
Interferon-alpha (IFN-α) can be produced as a recombinant human protein to treat some cancers. The gene IFNA2 codes for IFN-α. Genetically engineered E. coli contain recombinant…
Answer this question and get it marked →Meiosis is described as a reduction division because the number of chromosomes in the daughter cells is reduced by half. Table 5.1 describes events during four stages of meiosis…
Answer this question and get it marked →May–June 2023, Paper 41
List the four possible genotypes of the rabbit shown in Fig. 6.1 (a rabbit with short fur and the Himalayan colour pattern).
Answer this question and get it marked →Fig. 8.1 shows a cell from the testis of a locust at the late prophase I stage of meiosis. The photomicrograph shows several condensed chromosomes, some of which are paired and…
Answer this question and get it marked →May–June 2023, Paper 42
In sexual reproduction, meiosis occurs to produce haploid gametes from a diploid cell. Explain the meaning of the terms haploid and diploid.
Answer this question and get it marked →May–June 2023, Paper 43
An example of control of gene expression in prokaryotes is regulation in the lac operon. The lac operon is a length of DNA that is made up of different parts. Fig. 3.1 shows a…
Answer this question and get it marked →Table 5.2 shows the observed numbers obtained of each of the four different phenotypes for the F2 generation, compared with the numbers expected for a normal dihybrid ratio. Table…
Answer this question and get it marked →October–November 2023, Paper 11
The statements are about genes and proteins involved in breast cancer. The protein coded by the BRCA1 gene inhibits the growth of breast cancer cells. The protein coded by the p53…
Answer this question and get it marked →October–November 2023, Paper 41
The tiger barb, Puntigrus tetrazona, is a South American fish popular as an aquarium fish. Tiger barbs that show a wild-type phenotype are gold with black stripes; those with an…
Answer this question and get it marked →October–November 2023, Paper 42
The fruit fly, Drosophila melanogaster, has autosomal genes for body colour and wing shape. Gene B/b: B = dominant allele for brown body colour, b = recessive allele for black…
Answer this question and get it marked →October–November 2023, Paper 43
The tiger barb, Puntigrus tetrazona, is a South American fish that is popular worldwide as an aquarium fish. Fig. 6.1 shows the appearance (phenotype) of a normal (wild-type)…
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