Biology F215

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  • Created by: Liz
  • Created on: 09-06-11 16:48

Cellular control


  • A change in genetic material.
  • Point mutations are substitutions.
  • Insertion and deletion cause a frameshift.
  • Cystic fibrosis is deletion of a codon.
  • Sickle cell anaemia is a point mutation.
  • Huntington disease is caused by a repeated CAG sequence.

Lac operon

  • A repressor protein coded for by the regulatory gene prevents transcription of the two structural enzymes that metabolise lactose, by binding to the operator and blocking the promotor.
  • In the presence of lactose the repressor protein undergoes a conformational change in shape and falls away from the operator so that the structural genes (z) beta-galactosidase and (y) lactose permease can be transcribed.

Genes and body plans

  • Homeobox genes controll how the body plan develops.
  • Some genes determine the embryos polarity and others teh polarity of each segment.
  • Other genes identifiy the segments as individual parts.
  • Transcription factors nind to genes to initiate transcription and regulating expression of the other genes.
  • Homeobox genes are arranged in Hox clusters.


  • Prophase I - Chromatin condenses, chromosomes form bivalents, nucleus disappears.
  • Metaphase I - Bivalents attach to spindles, independent assortment.
  • Anaphase I - Chromosomes plled to poles.
  • Telophase I - Cytokinesis and new nucleus formed in new cells.
  • Prophase II - Nucleus breaks down and chromosomes condense.
  • Metaphase II - Chromosomes line up on equator and attach to spindles.
  • Anaphase II - Centromeres divide as chromatids pulled to poles.
  • Teleophase II - Nucleus reforms around haploid cells.


  • Nitric oxide can induce apoptosis.
  • Enzymes break down cytoskeleton.
  • Cytoplasm thickens and membrane changes and forms blebs.
  • Chromatin condenses and breaks into fragments and nuclear envelope breaks.
  • Cell breaks into vesicles that are taken in by phagocytes.

Genetic diagrams

  • Genotype - alleles present.
  • Homozygous - two identical alleles.
  • Heterozygous - two different alleles.
  • Phenotype - characteristics expressed.
  • Codominance - two different alleles expressed.
  • Linkage - two or more genes located on same chromosome.
  • Sex linkage - genes for characteristics are on sex chromosome. 
  • Epistasis is the interaction of different genes so that one masks or suppresses the expression of another.  


  • Used to test the significance of the difference between observed and expected results.
  • chi - squared = sum of (observed numbers - expected numbers) squared/ expected numbers

Continuous and discontinuous variation

  • Discontinuous - qualitative eg. blood groups. Different alleles for a single gene locus effect phenotype.
  • Continuous - quantitative eg. height. Controlled by two or more genes and each adds to the phenotype and then are on different chromosomes.

Population genetics

  • Hardy-Weinberg principle worked example. CFcf are symptomless carriers and cfcf have cystic fibrosis. 1/2000 have cystic fibrosis.
  • p represents frequency of dominant allele, CF.
  • q represents frequency of recessive allele, cf.
  • q² represents frequency of geneotype cfcf.
  • p² represents frequency of geneotype CFCF.
  • 2pq is the frequency of CFcf assuming random mating, where and two CFcf can mate to produce offspring that could be CFCF, CFcf, CFcf, cfcf. This translates to p²+ 2pq + q² .
  • p+q = 1 or 100%
  • p²+ 2pq + q² = 1


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