4(b) Inheritance
26 specification points in sub-topic 4(b).
Specification points
4.14: Genome and gene
The genome is all of an organism’s DNA; a gene is a section of DNA that codes for a protein.
4.15: Chromosomes and genes
Chromosomes: long DNA molecules carrying many genes in the nucleus.
4.16B: DNA structure
The structure of DNA: a double helix held together by complementary base pairs.
4.17B: RNA
How RNA differs from DNA in its sugar, bases and number of strands.
4.18B: Protein synthesis
Protein synthesis: transcription makes mRNA, then translation builds the protein.
4.19: Alleles
Alleles: different versions of the same gene.
4.20: Genetic terms
Dominant and recessive alleles, genotype, phenotype, homozygous and heterozygous.
4.21B: Codominance
Codominance: both alleles show in the phenotype, as in blood group AB.
4.22: Polygenic inheritance
Characteristics such as height are controlled by many genes and vary continuously.
4.23: Monohybrid inheritance diagrams
Genetic diagrams for one gene, from parents’ genotypes to offspring.
4.24: Family pedigrees
Reading family pedigrees to work out how a characteristic is inherited.
4.25: Probabilities from monohybrid crosses
Probabilities, ratios and percentages from monohybrid crosses, and why real results differ.
4.26: Sex chromosomes
Humans have 22 pairs of autosomes and one pair of sex chromosomes, XX or XY.
4.27: Sex determination
How the sperm carrying an X or a Y chromosome decides the sex of a baby.
4.28: Mitosis
Mitosis: one division that makes two genetically identical diploid cells.
4.29: Where mitosis occurs
Where and why mitosis happens: growth, repair and asexual reproduction.
4.30: Meiosis and haploid gametes
Meiosis: two divisions that make four varied haploid gametes.
4.31: Random fertilisation and variation
How meiosis and random fertilisation create genetic variation.
4.32: Human diploid and haploid numbers
Human body cells have 46 chromosomes (diploid); gametes have 23 (haploid).
4.33: Genetic and environmental variation
Variation caused by genes, by the environment, or by both together.
4.34: Mutation
Mutations: changes in DNA that create new alleles.
4.35B: A DNA change and the phenotype
How a change in DNA can change a protein and the phenotype.
4.36B: How often a mutation affects the phenotype
Why most mutations do not change the phenotype, and only rarely does one have a big effect.
4.37B: Ionising radiation and chemical mutagens
How ionising radiation and some chemicals increase the rate of mutation.
4.38: Darwin’s theory of evolution by natural selection
Natural selection: how better-adapted individuals pass on their alleles and populations evolve.
4.39: Antibiotic resistance in bacteria
How antibiotic resistance in bacteria evolves by natural selection.