Topic 6 definitions

• gamete


  sex cell
• chromosome


  strand of DNA
• gene


  a small section of DNA that codes for a particular sequence of amino acids to make a specific protein
• allele


  Different forms of a gene
• dominant allele


  always expressed, even if only one copy is present
• recessive allele


  only expressed if two copies are present
• homozygous


  an organism with identical alleles for a characteristic
• Heterozygous


  an organism with different alleles for a characteristic
• genotype


  genetic makeup of an organism
• phenotype


  physical characteristics of an organism
• How are dominant alleles shown

  capital letters B or P
• How are recessive allies shown

  lower letters b or p
• Disavantages of punnet square

  doesn't show phenotype
• Polydactyly


  extra fingers or toes caused by dominant allele
• cystic fibrosis


  cell membrane disorder sticky music in airways of the lungs caused by recessive allele
• Arguments for embryo scanning

  could reduce healthcare costs for foetus once born

  could avoid life of pain and suffering
• arguments against embryo screening


  expensive

  risk of miscarriage

  no cures for genetic disorders

  implies that people with genetic disorders are undesirable
• what is variation


  Any difference between individuals of the same species.
• what is variation caused by:

  - genetic

  - environmental

  - combination of both
• What is a mutation?

  change in DNA sequence

  - most have no effect on phenotype

  - rarely influences phenotype
• in organisms mutations:


  occur continuously

  rarely lead to a new phenotype

  if one is suited to an environmental change it can lead to a rapid change in the species by survival of the fittest.
• what is evolution


  the change in the inherited characteristics of a population over time through natural selection which may lead to the formation of a new species.
• what is selective breeding


  the process by which humans breed plants and animals for particular genetic characteristics.
• What is genetic engineering?


  process which involves modifying the genome of an organisms by introducing a gene from another organism to give a desired characteristic
• what are fossils?


  The 'remains' of organisms from millions of years ago, which are found in rocks
• what is extinction


  The permanent loss of all members of a species.