GCSE›Edexcel GCSE Biology›Mind mapsInheritanceEdexcel GCSE Biology: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsDNADouble helix of two strandsComplementary base pairs joined by weak hydrogen bondsNucleotide = sugar + phosphate + baseGene = DNA section coding for a proteinGenome = all the DNA of an organismMaking proteinRNA polymerase makes complementary mRNAmRNA attaches to a ribosomeCodon = 3 bases coding for an amino acidtRNA delivers matching amino acidsAmino acids join into a polypeptideGenetic termsAllele = alternative version of a geneDominant shows with one copyRecessive needs two copiesGenotype = alleles; phenotype = characteristicHomozygous = identical; heterozygous = differentInheritanceDNA, genes and crossesCrossesBb × Bb gives BB, Bb, Bb, bbRatio 3 brown : 1 blue, 25% blue-eyedSex: XX female, XY male, ratio 1:1ABO groups show codominance and multiple allelesSex-linked disorders affect males moreVariationMutations are random DNA changes, mostly no effectNon-coding variants change protein quantityCoding variants change protein activityHuman Genome Project aids diagnosis and counsellingExam tipsGenotype is alleles, phenotype is the resultGive crosses as probability, ratio or percentageOrder: polymerase, mRNA, ribosome, tRNA, polypeptide