Patterns of Inheritance | OCR A-Level Biology B (Advancing Biology) (H422)
Patterns of Inheritance
- 78 questions
- 5 subtopics
- Biology content, examined on all three papers
- Component 01, Component 02 and Component 03
Patterns of Inheritance is examined in all three written papers — the specification states that Components 01, 02 and 03 can each assess content from any of the five modules, so nothing is confined to one paper.
It covers monogenic inheritance and genetic terminology, gene mutations and inherited disease, codominance, multiple alleles and linkage, model organisms, dihybrid crosses and the chi-squared test and chromosome mutations and genetic counselling.
Sample questions from Patterns of Inheritance
Answer each one closed book first, then open the answer.
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Monogenic inheritance and genetic terminology
What does it mean to say an organism is homozygous for a gene?
Show the answer
It carries two identical alleles of that gene, one at the same locus on each of its two homologous chromosomes. -
Monogenic inheritance and genetic terminology
A plant heterozygous for one gene is self-pollinated. State the expected genotypic and phenotypic ratios of the offspring.
Show the answer
The expected genotypic ratio is 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive, which gives a 3 : 1 phenotypic ratio. -
Gene mutations and inherited disease
The commonest cystic fibrosis mutation deletes three bases. Explain why this does not cause a frameshift.
Show the answer
Three bases make one complete triplet, so a single amino acid, phenylalanine, is lost and every triplet after it is still read in the correct frame. -
Gene mutations and inherited disease
Why does untreated phenylketonuria damage the developing brain?
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Phenylalanine and the phenylketones derived from it build up to toxic concentrations in the blood and disrupt the normal development of the brain in infancy. -
Codominance, multiple alleles and linkage
A blood group A parent and a blood group B parent are both heterozygous. State the expected ratio of blood groups among their children.
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All four groups are expected, in a ratio of 1 group AB : 1 group A : 1 group B : 1 group O. -
Codominance, multiple alleles and linkage
Why is haemophilia far commoner in males than in females?
Show the answer
Males have only one X chromosome, so a single recessive allele is expressed, whereas a female must inherit the allele on both of her X chromosomes to be affected. -
Model organisms, dihybrid crosses and the chi-squared test
State the phenotypic ratio expected when two individuals heterozygous for two unlinked genes are crossed.
Show the answer
The expected phenotypic ratio is 9 : 3 : 3 : 1. -
Model organisms, dihybrid crosses and the chi-squared test
How are the degrees of freedom found for a chi-squared test on a genetic cross?
Show the answer
The degrees of freedom are one fewer than the number of phenotypic classes, so a 3 : 1 ratio gives 1 and a 9 : 3 : 3 : 1 ratio gives 3.
The 5 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Monogenic inheritance and genetic terminology | Recall questions on genes, alleles and loci, genotype and phenotype, homozygous and heterozygous, dominant, recessive and codominant alleles, carriers, monohybrid crosses and their ratios, cystic fibrosis probabilities, and the test cross. | 14 |
| Gene mutations and inherited disease | Recall questions on substitution, insertion, deletion and frameshift mutations, cystic fibrosis and the CFTR chloride channel, sickle cell anaemia and the GAG to GTG change, phenylketonuria and phenylalanine hydroxylase, and Huntington's disease and its CAG repeat. | 18 |
| Codominance, multiple alleles and linkage | Recall questions on multiple alleles and the Iᴬ, Iᴮ and Iᴼ alleles, ABO genotypes and crosses, codominant HLA antigens on chromosome 6 and transplant matching, sex linkage and haemophilia, and autosomal linkage, nail-patella syndrome and recombinant percentages. | 17 |
| Model organisms, dihybrid crosses and the chi-squared test | Recall questions on Drosophila melanogaster as a model organism, dihybrid crosses and the 9 : 3 : 3 : 1 ratio, independent assortment, and the chi-squared test with its null hypothesis, formula, degrees of freedom, worked calculation and critical values. | 14 |
| Chromosome mutations and genetic counselling | Recall questions on chromosome and gene mutations, non-disjunction and translocation, Down's syndrome and maternal age, Turner's and Klinefelter's syndromes, reading pedigrees for recessive and X-linked conditions, prenatal tests, and the ethics and non-directive nature of genetic counselling. | 15 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
OCR A-Level Biology B (Advancing Biology) Active Recall Guide
Every topic, not just this one. 2,895 questions with their answers.