BRAINCAKEGenetic Information
Revision notes for Genetic Information in Edexcel Biology B (9BI0). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.
- Meiosis and Genetic VariationMeiosis is the type of cell division that produces gametes.
- Mutation and Genetic VariationA mutation is a change in the base sequence of DNA.
- Different Types of MutationGene mutations that affect one or a few bases are called point mutations.
- Random FertilisationFertilisation is the fusion of a male gamete and a female gamete to form a zygote.
- Genetics and InheritanceGenetics is the study of how characteristics are passed from parents to offspring.
- AllelesAn allele is a different version of the same gene.
- Polygenic TraitsSome characteristics are controlled by a single gene (monogenic).
- Monohybrid CrossesA monohybrid cross follows the inheritance of one characteristic controlled by a single gene with two alleles.
- Test CrossAn organism showing a dominant phenotype could be homozygous dominant (TT) or heterozygous (Tt), because both look the same.
- Sampling ErrorsGenetic crosses predict expected ratios, such as 3 : 1 or 1 : 1.
- MendelGregor Mendel was a monk working in what is now the Czech Republic.
- Law of SegregationMendel's first law is the law of segregation.
- Law of Independent AssortmentMendel's second law is the law of independent assortment.
- Multiple AllelesMany genes have multiple alleles: three or more alleles of the gene exist in the population.
- CodominanceAlleles are codominant when both alleles are expressed in the phenotype of a heterozygote.
- Dihybrid CrossesA dihybrid cross follows the inheritance of two characteristics, each controlled by a different gene, at the same time.
- DrosophilaThe fruit fly Drosophila melanogaster is one of the most important model organisms in genetics.
- ProbabilityGenetic ratios are really probabilities.
- Chi-Squared TestThe chi-squared (χ2) test is a statistical test used to decide whether the difference between observed (O) and expected (E) results is significant…
- Chi-Squared Test - Monohybrid CrossesFor a monohybrid cross there are normally two phenotype categories, so there is 2 − 1 = 1 degree of freedom, and the critical value at p = 0.05 is…
- Chi-Squared Test- Dihybrid CrossesFor a dihybrid cross there are usually four phenotype categories, so there are 4 − 1 = 3 degrees of freedom, and the critical value at p = 0.05 is…
- Gene LinkageEach chromosome carries hundreds or thousands of genes.
- Identifying Linked GenesLinkage is usually identified from the results of a dihybrid test cross, in which a double heterozygote (AaBb) is crossed with a double homozygous…
- Chromosome MappingThe further apart two genes are on a chromosome, the more likely it is that a chiasma forms between them and separates their alleles.
- Sex-LinkageIn humans, sex is determined by the sex chromosomes.
- Pedigree DiagramsA pedigree diagram (family tree) shows how a characteristic is inherited through several generations of a family.
- The Albino TraitAlbinism is an inherited condition in which the body makes little or no melanin, the pigment that colours skin, hair and the iris of the eye.
- Sex-Linked DiseasesSex-linked diseases are caused by faulty alleles of genes on the sex chromosomes.
- Red-Green Colour BlindnessRed-green colour blindness is the most common sex-linked condition.
- HaemophiliaHaemophilia is a sex-linked condition in which the blood does not clot properly.
On the specification
- 8.1 Origins of genetic variation
- 8.2 Transfer of genetic information