BRAINCAKE

Genetics and Variation

OCR A-level BiologyTopic 8 of 936 lessons

Revision notes for Genetics and Variation in OCR Biology A (H420). 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.

  1. The Genetic CodeThe genetic code is a triplet code.
  2. MutationsA mutation is a change in the sequence of bases in DNA.
  3. Effects of MutationsNo effect - the protein may function as normal.
  4. Change in Protein FunctionAmorph effect - the mutation results in a loss of function of the protein.
  5. Sickle-cell AnaemiaIn sickle cell anaemia, abnormal haemoglobin clumps together deforming the shape of red blood cells and causing them to become sickle shaped.
  6. Causes of mutationsMutations occur spontaneously, usually during DNA replication.
  7. Chromosome MutationsIf the number of chromosomes in a cell changes as in Down's syndrome, or the mutation affects the whole chromosome, this is known as a chromosome…
  8. Gene RegulationHousekeeping genes are genes that code for enzymes and proteins that are constantly needed for the normal functioning of the cells and are…
  9. Controlling TranscriptionDNA is wound round histone proteins.
  10. Lac OperonThe lac operon is a set of genes expressed at the same time and under the regulation of the same regulatory mechanism.
  11. cyclic AMPWhen cAMP receptor protein (CRP) is bound to cyclic AMP it can bind to the promoter and enhance the rate of transcription by RNA polymerase…
  12. Post-transcriptional controlTranscription results in a precursor to mRNA called pre-mRNA.
  13. Translational ControlmRNA degradation - the more resistant mRNA is to degradation the more protein will be made.
  14. Post-translational ControlModifications to proteins such as: addition of non-protein groups e.g. carbohydrate chains, lipids and phosphates modification of amino-acids…
  15. Homeobox GenesHomeobox genes are a group of genes which contain a particular sequence of 180 bases called a homeobox.
  16. Body PlansHox genes in animals are the homeobox genes that control body plans.
  17. ApoptosisApoptosis is programmed cell death which removes unwanted cells from the body.
  18. Regulatory GenesWhen an organisms is under stress the organs's homeostatic balance is upset.
  19. VariationVariation occurs as a result of random mutations and is important for the process of natural selection.
  20. Body MassThe body mass of an individual organism depends on both genetic and environmental factors.
  21. Genetic VariationThere are different versions of the same genes, called alleles During fertilisation one allele is inherited from each parent.
  22. Continuous and Discontinuous VariationVariation can be continuous or discontinuous.
  23. Genetic CrossPunnett squares are used to show genetic crosses.
  24. Sex LinkageIn humans, there are 23 pairs of homologous chromosomes.
  25. Dihybrid CrossesThese are used to show the inheritance of two different genes on two different chromosomes.
  26. LinkageGenes which are inherited together because they are on the same chromosome are called linked genes.
  27. Χ-squared TestThe Chi-squared test is a statistical test that measures the difference between the observed and expected values and tests whether or not the…
  28. EpistasisEpistasis is the interaction of different genes at different loci.
  29. The Hardy-Weinberg PrincipleAll the genes in a population at a given time is known as the gene pool.
  30. Changes in Allele FrequenciesMutation leads to the formation of new alleles.
  31. Population Bottlenecks and The Founder EffectIf in a particular generation, the size of a population suddenly and drastically reduces this is known as a population bottleneck and extreme form…
  32. Types of SelectionVariation within organisms follows a normal distribution or bell-shaped curve.
  33. SpeciesNew species can be formed through the process of natural selection and evolution.
  34. Allopatric SpeciationAllopatric speciation occurs when a physical barrier arises between members of a population.
  35. Sympatric SpeciationSympatric speciation occurs more commonly in plants than animals and occurs less than allopatric speciation.
  36. Artificial SelectionArtificial selection is selective breeding by humans for desired characteristics.

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