Genes, Inheritance and Selection

What Genes, Inheritance and Selection covers

Genes, Inheritance and Selection is examined in Paper 8 (Biology). It covers genetic terms and the genome; genome, environment and mutations; haploid, diploid and meiosis; single gene inheritance and Punnett squares; sex determination and characteristics controlled by multiple genes; variation within a population and classification; natural selection and evolution; and fossils and antibiotic resistance as evidence for evolution.

The 8 subtopics

Each one has its own page.

• Genetic terms, and the genomeWhat gametes, chromosomes, genes and alleles are, dominant and recessive alleles, homozygous and heterozygous, genotype and phenotype, writing genotypes and working out a phenotype, what a genome is and that it includes non-coding DNA, how a gene and a genome differ, where the genome is found, why individuals' genomes differ, and what sequencing a genome means.Open →
• Genome, environment and mutationsHow the genome and the environment together determine phenotype, discontinuous and continuous variation with examples such as eye colour and height and how each is usually controlled, mutations as the source of all genetic variants, the three possible effects of a mutation on the phenotype and which is rarest, why most have no effect, and why not all mutations are harmful.Open →
• Haploid, diploid and meiosisWhat haploid and diploid mean, human chromosome numbers in body cells and gametes, why a fertilised egg and an embryo's cells are diploid, how meiosis halves the chromosome number to make four gametes, how meiosis and fertilisation keep the number constant, meiosis as a source of variation, where it happens, and how it compares with mitosis.Open →
• Single gene inheritance and Punnett squaresWhat single gene inheritance is, predicting offspring genotypes and phenotypes from crosses of homozygous and heterozygous parents, what a carrier is and why a recessive characteristic needs two recessive alleles, a test cross to find an unknown genotype, using Punnett squares to give ratios, numbers and probabilities, and why each fertilisation is independent.Open →
• Sex determination and characteristics controlled by many genesThe X and Y chromosomes and which parent decides a child's sex, the Punnett square for the cross and the chance of a boy, characteristics controlled by many genes, and why they are harder to predict than a single gene cross.Open →
• Variation within a population, and classificationHow much genetic variation a population holds and where it comes from, why individuals carry the same genes in different variants, why variation helps a population and sexual reproduction gives more of it, what classification is, artificial and natural classification with examples, molecular phylogenetics and how DNA sequencing reveals relationships, and why classification changes over time.Open →
• Natural selection and evolutionWhat natural selection is, where variation comes from, the steps from mutation to a changed population, why individuals do not evolve, what evolution and a species are, and how new species form.Open →
• Evidence for evolution from fossils and antibiotic resistanceFossils and antibiotic resistance as evidence for evolution, why the fossil record is incomplete, how bacteria become resistant to an antibiotic and why they evolve so quickly, and why stopping a course of antibiotics early helps resistance spread.Open →

What you need to know

Answer each one before you reveal it.

Take Genes, Inheritance and Selection further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Genotype vs Phenotype

  Genotype: combination of alleles an organism carries for a gene. Phenotype: observable characteristics of an organism.

• Homozygous vs Heterozygous

  Homozygous: carrying two identical alleles of a gene. Heterozygous: carrying two different alleles of a gene.

• Haploid vs Diploid

  Haploid: containing a single set of chromosomes, one copy of each. Diploid: containing two sets of chromosomes, one inherited from each parent.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What is a gamete?

   Model answer

   A sex cell that carries a single set of chromosomes and fuses with another gamete at fertilisation.

2. 2

   What is a chromosome?

   Model answer

   A long coiled molecule of DNA, found in the nucleus, that carries many genes along its length.

3. 3

   What is a gene?

   Model answer

   A section of DNA that codes for a particular protein and so contributes to a characteristic.

4. 4

   What is an allele, also called a variant?

   Model answer

   A different version of the same gene, found at the same position on a chromosome.

5. 5

   What does it mean to say that an allele is dominant?

   Model answer

   Only one copy of it is needed for it to be shown in the phenotype.

6. 6

   What does it mean to say that an allele is recessive?

   Model answer

   Two copies of it are needed for it to be shown, because a dominant allele masks it whenever one is present.

What is inside Levo

Six ways to work the same material.

Genes, Inheritance and Selection revision questions

What does Genes, Inheritance and Selection cover in OCR GCSE Combined Science Biology?

8 subtopics: genetic terms, and the genome, genome, environment and mutations, haploid, diploid and meiosis, single gene inheritance and punnett squares, sex determination and characteristics controlled by many genes, variation within a population, and classification, natural selection and evolution and evidence for evolution from fossils and antibiotic resistance. Each one has its own page with questions and model answers.

How is Genes, Inheritance and Selection organised?

By the OCR J250 specification, subtopic by subtopic, so it matches the order you are taught it in.