Origins of Genetic Variation

What Origins of Genetic Variation covers

Where genetic variation comes from, how it is passed on through monohybrid, dihybrid and sex-linked crosses, how a chi-squared test judges whether results fit a prediction, and how allele frequencies change in a population.

The 8 subtopics

Each one has its own page.

• Mutation, meiosis and random fertilisationRecall questions on mutation, crossing over, independent assortment and random fertilisation as sources of variation.Open →
• Genotype, phenotype and monohybrid inheritanceRecall questions on the key terms, dominance and codominance, and constructing a monohybrid cross.Open →
• Dihybrid crosses and pedigree diagramsRecall questions on the symbols and lines of a pedigree diagram, what a dihybrid cross is, the 9:3:3:1 ratio, and why unlinked genes assort independently.Open →
• Autosomal linkage and sex linkageRecall questions on autosomal linkage and why linked genes do not assort independently, crossing over and recombinant phenotypes, body colour and wing length in Drosophila, and sex linkage, hemizygous males and the X-linked inheritance of haemophilia.Open →
• The chi-squared test in geneticsRecall questions on the null hypothesis, calculating the statistic, degrees of freedom, and interpreting the result against the critical value.Open →
• Selection pressures and allele frequencyRecall questions on selection pressures, stabilising selection and birth mass, disruptive selection, bimodal distributions and speciation, and why selection changes allele frequencies without creating new alleles.Open →
• Genetic drift and the founder effectRecall questions on chance change in small populations, genetic bottlenecks, and the founder effect.Open →
• The Hardy-Weinberg equationRecall questions on the conditions the principle assumes, using the two equations, and what a departure from equilibrium indicates.Open →

What you need to know

Answer each one before you reveal it.

Take Origins of Genetic Variation further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Gene mutation vs Chromosome mutation

  Gene mutation: change in the base sequence of DNA. Chromosome mutation: change in chromosome structure or number.

• Horizontal gene transfer vs Vertical gene transfer

  Horizontal gene transfer: movement of genetic material between organisms without reproduction. Vertical gene transfer: inheritance of genetic material from parent to offspring.

• Genetic drift vs Natural selection

  Genetic drift: random change in allele frequencies. Natural selection: non-random change caused by differential reproductive success.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is the ultimate source of new genetic variation in a population?

   Model answer

   Mutations are the ultimate source of new genetic variation, creating new alleles that did not previously exist in a population.

2. 2

   Why are mutations considered the only way to generate truly novel alleles?

   Model answer

   Mutations alter the DNA sequence itself, producing alleles that have never existed before, rather than simply rearranging pre-existing alleles.

3. 3

   During random assortment, where do homologous chromosome pairs align?

   Model answer

   Homologous pairs align independently at the metaphase plate during metaphase I.

4. 4

   Explain how the orientation of each homologous pair at metaphase I is determined.

   Model answer

   Each homologous pair can orient with either parental chromosome facing either pole; this orientation is random and independent of other pairs.

5. 5

   State the formula for the number of possible gamete combinations produced by independent assortment, and define the variable.

   Model answer

   The formula is 2ⁿ, where n is the haploid chromosome number.

6. 6

   At which stage of meiosis does crossing over occur?

   Model answer

   Crossing over occurs during prophase I when homologous chromosomes pair up.

What is inside Levo

Six ways to work the same material.

Origins of Genetic Variation revision questions

What does Origins of Genetic Variation cover in Edexcel A-Level Biology B?

8 subtopics: mutation, meiosis and random fertilisation, genotype, phenotype and monohybrid inheritance, dihybrid crosses and pedigree diagrams, autosomal linkage and sex linkage, the chi-squared test in genetics, selection pressures and allele frequency, genetic drift and the founder effect and the hardy-weinberg equation. Each one has its own page with questions and model answers.

How is Origins of Genetic Variation organised?

By the Edexcel 9BI0 specification, subtopic by subtopic, so it matches the order you are taught it in.