Genetics

• DNA

  Deoxyribonucleic acid, the chemical that all of our genetic material is made of
• DNA

  • It's a polymer made up of lots of similar units stuck together
  • It has two strands which are stuck together to form a double helix
• If you unraveled all the DNA in a single cell, the strand would be over two meters long</b>
• Chromosome


  A really tight coil of DNA, there are 46 chromosomes in each of our cells
• There are 23 different types of chromosomes, with two of each type (one from each parent)
• Sex chromosomes

  The 23rd pair, consisting of an X chromosome and a Y chromosome
• Females have two X chromosomes, males have one X and one Y
• Chromosomes only look like an X shape just before cell division
• Gene


  A small section of DNA that codes for a particular type of protein
• There are 20 different types of amino acids, which can be combined in many different sequences to form thousands of different proteins
• Genome

  The entire set of genetic material in an organism
• Scientists have worked out the complete human genome, which allows them to identify genes linked to diseases
• Differences in genomes between populations can tell us about human migrations
• Genes are sections of DNA that code for specific traits or functions.
• DNA contains genetic information that determines an organism's characteristics.
• Allele


  Different versions of the same gene
• Homozygous


  Having two of the same alleles for a particular gene
• Heterozygous


  Having two different alleles for a particular gene
• Dominant allele


  The allele that gets expressed when present, regardless of whether the organism is homozygous or heterozygous for that allele
• Recessive allele


  The allele that only gets expressed when the organism is homozygous for that allele
• Genotype


  The entire collection of alleles that an organism has
• Phenotype


  The characteristics that an organism displays, which are determined by its genotype
• Genes code for particular types of proteins
• There are often multiple forms of the same protein, and each form has a different genetic code
• We have two copies of every gene, one from each parent
• If the two alleles are the same, the organism is homozygous for that allele
• If the two alleles are different, the organism is heterozygous
• In a heterozygous organism, one allele will be dominant and the other will be recessive
• The dominant allele will always be expressed, regardless of whether the organism is homozygous or heterozygous for that allele
• The only way to have a recessive trait expressed is if the organism is homozygous for the recessive allele
• Organisms with different genotypes can have the same phenotype, and organisms with the same genotype can have different phenotypes