b5

• gamete


  sex cells (egg or sperm)
• chromosome

  tightly packed dna around histone proteins
• gene


  a section of dna that can code for a protein
• allele

  different version of the same gene
• dominant allele


  a version of a gene where only one copy is needed for it to be expressed
• recessive gene


  a version of a gene where two copies are needed for it to be expressed
• homozygous


  two copies of the same allele
• heterozygous

  two different versions of the same gene
• genotype

  the genes present for a trait
• phenotype

  the visible characteristic
• genome

  all the genes present in an organism
• discontinuous variation


  variation that produces distinct categories (e.g. eye colour, blood type)
• continuous variation


  variation that cannot be placed into distinct categories and instead produces a spectrum (e.g. height, weight)
• what causes variation?

  mutations in genetic code
• describe how a mutation in a coding DNA sequence could be detrimental

  • the mutation may change the sequence of amino acids in the protein which will change its structure
  • this may affect the protein, particularly in specific molecules like enzymes and antibodies
• what may happen if there is a mutation in non coding dna?

  it may stop transcription and alter the expression of genes
• one advantage and one disadvantage of sexual reproduction

  • advantage - produces variation
  • disadvantage - is slower and produces a limited amount of offspring
• one advantage and one disadvantage of asexual reproduction

  • advantage - produces lots of offspring quickly
  • disadvantage - does not introduce variation so all offspring are susceptible to the same environmental pressures as parents
• difference between diploid and haploid cells

  • haploid cells have half the amount of genetic information as diploid cells
  • haploid cells are germ cells
  • diploid cells are body cells
• what type of cell does meiosis produce?

  haploid germ cells (egg and sperm cells)
• how are dominant alleles represented in a punnett square?

  they are represented using uppercase letters
• how are recessive alleles represented in a punnett square?

  they use the lowercase version of the same letter as the dominant allele
• give three important findings of Gregor Mendel

  • organisms inherit hereditary units from their parents
  • offspring receive units from both parents and so share traits with both parents
  • traits can be passed on but not visible
• what discovery lead to people accepting Mendel's ideas?

  the discovery of the gene
• phylogenetics

  the study of evolutionary relationships
• three advancements that improved classification

  • developments in microscopy
  • developments in biochemistry
  • new dna evidence
• process of natural selection

  • populations are naturally varied due to random genetic mutations
  • some of these mutations provide a selective adavantage
  • these organisms survive and reproduce, passing on the successful genes
• evolution


  change in the genetic makeup of a population over time due to natural selection
• two pieces of evidence for evolution

  • fossils
  • antibiotic resistance
• describe how antibiotic resistance arises

  • a random genetic mutation causes a bacterium to become resistant to the antibiotic
  • when the antibiotic is used, all the bacteria that do not have the mutation are killed
  • the population containing just the resistant bacteria then begins to grow
• describe how two new species develop from one species

  • a population is split where members of the population are isolated
  • the environments become different and so natural selection will occur differently
  • the two groups will become different enough that they cannot breed to produce fertile offspring anymore
• why was Darwin's theory only slowly accepted?

  • most people still believed God created all the life on earth
  • there was insufficient evidence to support his theory at the time