DNA and inheritance

• DNA

  The material inside the nucleus of cells, carrying the genetic information of a living being.
• Organism

  Living entity, eg animals, plants or micro-organisms.
• Nucleus

  The nucleus controls what happens inside the cell. Chromosomes are structures found in the nucleus of most cells.
• Chromosome

  The structure made of DNA that codes for all the characteristics of an organism.
• Gene

  The basic unit of genetic material inherited from our parents. A gene is a section of DNA which controls part of a cell's chemistry - particularly protein production.
• Allele

  Different versions of the same gene.
• Genotype

  The genes an organism contains
• Phenotype

  The visible characteristics of an organism
• Dominant allele

  An allele that always expresses itself whether it is partnered by a recessive allele or by another like itself.
• Recessive allele

  Describes the variant of a gene for a particular characteristic which is masked or suppressed in the presence of the dominant variant.
• Homozygous

  contains the same alleles (BB or bb)
• Heterozygous

  Contains different alleles (Bb)
• DNA

  Large and complex molecules that carry the genetic code that determines the characteristics of a living organism
• Gene

  A section of DNA that codes for a specific protein
• Chromosome

  Long threads of DNA, each made up of many genes, found in the nucleus of most cells
• DNA structure

  • Two strands coiled into a double helix
  • Backbone made from alternating sugar and phosphate molecules
  • Paired chemicals (bases) between the strands
• Base pairs

  Chemical bonds between the two DNA strands, formed by pairs of bases (thymine-adenine, guanine-cytosine)
• Triplet code

  Sequence of three bases that determines the sequence of amino acids in a protein
• The order of bases in genes determines the order of amino acids which create a specific protein
• Some characteristics are controlled by a single gene, while others are controlled by multiple genes
• Allele

  Different forms of the same gene
• DNA

  Hereditary molecule responsible for its function
• Genetic cross

  Examination and showing of possible offspring combinations using a Punnett square
• Carrying out a genetic cross

  1. Determine probability of offspring combinations

  2. Calculate ratios of offspring combinations
• Monohybrid cross

  Genetic cross of single gene combinations
• Dominant allele


  Should always be written first
• Self-pollination

  Pollen from one flower lands on the stigma of the same flower
• Most phenotypes are controlled by multiple genes
• Punnett square


  A diagram used to predict the possible genotypes of offspring
• Human body cells

  • Have 23 pairs of chromosomes
  • 22 pairs are autosomes
  • 1 pair determines sex
• Sex chromosomes

  • Males have XY
  • Females have XX
• Combination of sex chromosomes


  Determines biological gender (sex)
• The probability of having a girl (XX) or a boy (XY) is 50%
• Genetic profiling

  Technique used to create and use DNA profiles
• How to produce a DNA fingerprint

  1. Isolation

  2. Fragmentation

  3. Separation (gel electrophoresis)

  4. Comparison
• Using DNA profiling in solving crimes

  • DNA is often left at the scene of a crime (blood, skin, hair)
  • DNA profiling can be used to place a suspect at the crime scene
• When DNA profile of suspect matches DNA profile found at crime scene

  Suspect has left their DNA at the crime scene
• Using DNA profiles to determine paternity

  • DNA profile of baby and mother must be known
  • Any band in baby's DNA profile not found in mother's must be present in father's DNA profile
• When a band in baby's DNA profile is not found in mother's DNA profile, but is found in father's DNA profile


  The father is confirmed
• Genetic profiling

  • Can be used to identify alleles associated with genetic disorders
  • Allows early identification and treatment of genetic disorders