Genetics

What Genetics covers

Genetics is examined in Paper 1, Biology 1. It covers asexual and sexual reproduction, meiosis, DNA structure, genes and the genome, extracting DNA from fruit, protein synthesis and the effects of genetic variants, Mendel's work and the inheritance of blood groups, alleles, genotype and phenotype, monohybrid crosses, sex determination and probability, sex-linked disorders, genetic and environmental variation, the Human Genome Project and mutation.

The 14 subtopics

Each one has its own page.

• Asexual and sexual reproductionAsexual reproduction producing clones, its advantages of needing no mate and reproducing rapidly and the risk its lack of variation brings, and how fertilisation in sexual reproduction produces variation that helps a population survive disease and changing conditions.Open →
• Meiosis and the formation of gametesWhere meiosis takes place, the four haploid daughter cells it makes with half the chromosome number, the 23 chromosomes in a human gamete, why gametes must be haploid for fertilisation, and how the random sharing of chromosomes makes gametes and children genetically different.Open →
• DNA structure, genes and the genomeDNA as a double helix polymer of nucleotides made of a sugar, a phosphate and one of four bases, complementary base pairing held by weak hydrogen bonds, genes as sections of DNA coding for proteins, the genome, and why people with the same genes can differ.Open →
• Extracting DNA from fruitExtracting DNA from fruit by mashing, adding detergent and salt, filtering and pouring on ice-cold ethanol, why the DNA comes out of solution as a white stringy layer, and why the mixture is stirred gently.Open →
• Protein synthesis: transcription and translationHow the base order sets the amino acid order and the protein's shape, then transcription by RNA polymerase, mRNA, codons, tRNA and the ribosome joining a polypeptide.Open →
• Genetic variants in coding and non-coding DNAWhere the non-coding DNA lies, how a variant there changes how much protein is made, and how a variant in coding DNA alters the amino acid sequence and the protein's activity.Open →
• Mendel's work and the inheritance of blood groupsMendel's pea plant crosses, the 3:1 ratio, why his ideas were slow to be accepted, and the three ABO alleles, codominance and the blood groups they give.Open →
• Alleles, genotype and phenotypeAlleles and why individuals of a species differ, dominant and recessive alleles and how a recessive allele can be carried unseen, chromosomes and genes, homozygous and heterozygous, genotype and phenotype, gametes and zygotes, and why one phenotype can hide different genotypes.Open →
• Monohybrid crosses and sex determinationMonohybrid inheritance and Punnett squares, the ratios from heterozygous and homozygous crosses, reading a family pedigree, and how the X and Y chromosomes decide sex.Open →
• Probability and ratios from genetic crossesThe probabilities and percentages expected from heterozygous and homozygous recessive crosses, turning offspring counts into whole-number ratios, and why real results rarely match the prediction.Open →
• Sex-linked disordersSex-linked disorders carried on the X chromosome such as red-green colour blindness, why males are affected more often, female carriers, why fathers cannot pass the allele to their sons, the chances from a carrier mother's cross, and how a daughter can be affected.Open →
• Causes of variation: genes and environmentCharacteristics controlled by many genes such as height and their continuous range, genetic variation from mutation and sexual reproduction, acquired characteristics and environmental variation, identical twins, and presenting variation with frequency tables, histograms, bar charts and the modal class.Open →
• The Human Genome ProjectThe aim and outcomes of the Human Genome Project, testing for inherited disorders and predicting disease risk, personalised medicine and new drug treatments, tracing human migration, and concerns about insurers, employers and knowing the risk of an untreatable disease.Open →
• Genetic variation and the effects of mutationExtensive genetic variation within a population, mutations as random changes in base sequence and the source of new variation, why most mutations have no effect on the phenotype, the rare ones that stop a protein working, and mutations that give an advantage.Open →

What you need to know

Answer each one before you reveal it.

Take Genetics 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 has for a characteristic. Phenotype: observable characteristic the organism actually shows.

• Homozygous vs Heterozygous

  Homozygous: having two identical alleles of a particular gene. Heterozygous: having two different alleles of a particular gene.

• Transcription vs Translation

  Transcription: making an mRNA copy of a gene inside the nucleus. Translation: joining amino acids at a ribosome in the order the mRNA codons set.

Questions from this topic

Each one with the model answer underneath.

1. 1

   How many parents are involved in asexual reproduction?

   Model answer

   Only one parent is involved in asexual reproduction.

2. 2

   How are offspring produced by asexual reproduction related to their parent genetically?

   Model answer

   They are genetically identical to the parent, so they are clones.

3. 3

   Explain why not needing a mate is an advantage of reproducing asexually.

   Model answer

   No time or energy is spent searching for a partner, so an isolated individual can still produce offspring.

4. 4

   Explain how a rapid reproductive cycle benefits an organism that reproduces asexually.

   Model answer

   Large numbers of offspring are produced quickly, so a favourable habitat can be colonised before competitors arrive.

5. 5

   Why is the lack of variation a disadvantage of asexual reproduction?

   Model answer

   All the offspring have the same alleles, so none of them is better suited to a change in conditions.

6. 6

   Explain why a new disease can wipe out an entire population of asexually produced organisms.

   Model answer

   Every individual is genetically identical, so if one is susceptible to the pathogen they all are.

What is inside Levo

Six ways to work the same material.

Genetics revision questions

What does Genetics cover in Edexcel GCSE Biology?

14 subtopics: asexual and sexual reproduction, meiosis and the formation of gametes, dna structure, genes and the genome, extracting dna from fruit, protein synthesis: transcription and translation, genetic variants in coding and non-coding dna, mendel's work and the inheritance of blood groups, alleles, genotype and phenotype, monohybrid crosses and sex determination, probability and ratios from genetic crosses, sex-linked disorders, causes of variation: genes and environment, the human genome project and genetic variation and the effects of mutation. Each one has its own page with questions and model answers.

How is Genetics organised?

By the Edexcel 1BI0 specification, subtopic by subtopic, so it matches the order you are taught it in.