Patterns of Inheritance

What Patterns of Inheritance covers

Patterns of inheritance is the second section of Module 6. It covers what makes a phenotype vary, monogenic and dihybrid crosses and the patterns that depart from them, the chi-squared test, the forms of selection and the drift acting on small populations, the Hardy-Weinberg equations, speciation, and artificial selection.

The 7 subtopics

Each one has its own page.

• Genetic and environmental variationThe genetic and environmental factors behind a phenotype, etiolation as a worked example, and the meiosis and random fertilisation that generate variation.Open →
• Monogenic and dihybrid inheritance, sex linkage and epistasisMonogenic and dihybrid crosses and the expected ratios, multiple alleles, codominance and sex linkage, and the modified ratios that reveal linkage and epistasis.Open →
• The chi-squared testWhat the test is for, the formula and what each term means, how degrees of freedom are found, and when the null hypothesis is rejected.Open →
• Selection, genetic drift and the founder effectStabilising and directional selection and what each does to variation, and the drift, bottlenecks and founder effects that act on small populations.Open →
• The Hardy-Weinberg principleThe allele and genotype frequency equations and what each term represents, and the order in which q, then p, then the genotype frequencies are calculated.Open →
• Speciation and isolating mechanismsAllopatric and sympatric speciation, and the temporal, behavioural, mechanical and gametic isolation that keeps populations from interbreeding.Open →
• Artificial selectionWhat is selected for in crops and in livestock, how the selective pressure differs from natural selection, and the loss of diversity and welfare problems that can follow.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.

• Codominance vs Epistasis

  Codominance: equal expression of both alleles in a heterozygote. Epistasis: one gene modifies or masks expression of another locus.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What two broad categories of factors combine to produce phenotypic variation in organisms?

   Model answer

   Genetic factors and environmental factors.

2. 2

   How do genetic factors contribute to phenotypic variation?

   Model answer

   Different alleles and combinations of alleles inherited from parents produce different phenotypes.

3. 3

   How do environmental factors contribute to phenotypic variation?

   Model answer

   External conditions such as temperature, light, and nutrient availability can modify how genes are expressed, altering the phenotype.

4. 4

   Give an example of an environmental factor that contributes to phenotypic variation in animals.

   Model answer

   Diet.

5. 5

   How can diet affect phenotypic variation in animals?

   Model answer

   Nutrient availability influences growth, body mass, coat condition, and other physical characteristics.

6. 6

   What is etiolation in plants?

   Model answer

   Etiolation is the elongated, pale growth of plants that occurs when they are grown in the absence of light.

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?

7 subtopics: genetic and environmental variation, monogenic and dihybrid inheritance, sex linkage and epistasis, the chi-squared test, selection, genetic drift and the founder effect, the hardy-weinberg principle, speciation and isolating mechanisms and artificial selection. Each one has its own page with questions and model answers.

How is Patterns of Inheritance organised?

By the OCR H420 specification, subtopic by subtopic, so it matches the order you are taught it in.