Patterns of Inheritance

What Patterns of Inheritance covers

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.

The 5 subtopics

Each one has its own page.

• Monogenic inheritance and genetic terminologyRecall 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.Open →
• Gene mutations and inherited diseaseRecall 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.Open →
• Codominance, multiple alleles and linkageRecall 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.Open →
• Model organisms, dihybrid crosses and the chi-squared testRecall 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.Open →
• Chromosome mutations and genetic counsellingRecall 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.Open →

What you need to know

Answer each one before you reveal it.

Take Patterns of Inheritance further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Gene vs Allele

  Gene: a length of DNA at a fixed position on a chromosome that codes for one polypeptide. Allele: one of the alternative base sequences that can occupy that same position, giving a different version of the characteristic.

• Genotype vs Phenotype

  Genotype: the particular combination of alleles an organism carries for a characteristic. Phenotype: the observable characteristics that result from those alleles acting together with the environment.

• Gene mutation vs Chromosome mutation

  Gene mutation: a change to the base sequence within one length of coding DNA, such as a substitution, an insertion or a deletion of bases. Chromosome mutation: a change to the karyotype, altering either the number of whole structures present or their arrangement, as in trisomy 21 or a translocation.

Questions from this topic

Each one with the model answer underneath.

1. 1

   Define the term gene.

   Model answer

   A gene is a length of DNA at a specific locus that codes for a polypeptide or for a functional RNA molecule.

2. 2

   What is an allele, and where are the two alleles of a gene found?

   Model answer

   An allele, or gene variant, is one of the alternative base sequences of a gene, and the two alleles of a gene occupy the same locus on a pair of homologous chromosomes.

3. 3

   Define the term locus.

   Model answer

   The locus is the fixed position that a particular gene occupies on a chromosome.

4. 4

   What is the difference between the genotype and the phenotype of an organism?

   Model answer

   The genotype is the combination of alleles the organism carries, while the phenotype is the observable characteristics produced when that genotype interacts with the environment.

5. 5

   What does it mean to say an organism is homozygous for a gene?

   Model answer

   It carries two identical alleles of that gene, one at the same locus on each of its two homologous chromosomes.

6. 6

   What does heterozygous mean?

   Model answer

   The organism carries two different alleles of the same gene at the same locus on its two homologous chromosomes.

What is inside Levo

Six ways to work the same material.

Patterns of Inheritance revision questions

What does Patterns of Inheritance cover in OCR A-Level Biology B?

5 subtopics: 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. Each one has its own page with questions and model answers.

How is Patterns of Inheritance organised?

By the OCR H422 specification, subtopic by subtopic, so it matches the order you are taught it in.