BRAINCAKEGenetic Information
Revision notes for Genetic Information in Edexcel Biology (9BI0). Read the start of any lesson here, then sign in free for the whole lesson, the R.E.C.I.P.E. recall steps and the quiz.
- 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.