genetics / reproduction

• chromasomes

  human bodies typically have 23 pairs of chromasomes

  carry genetic information through DNA
• gene


  a gene is a small section of DNA on a chromasome, each gene codes for a particular sequence of amino acids, to make a specific protein. This is the codes for protein that control our characteristics.
• DNA


  DNA is a polymer - deoxyribonuleicacid.

  the spiral shape if DNA is called a double helix.
• Asecual reproduction

  1. cell grows by making new organelles
  2. the DNA is replicated / copied (now each chromasome is made of 2 chromatids (interphase )).
  3. the nucleus breaks down (mitosis)
  4. spindle fibres pull one chromasome from each pair to either end of the cell (mitosis)
  5. the nucleus reforms (mitosis)
  6. the cell divides into 2 genetically identical cells (cytokenisis)
• Sexual reproduction

  1. fusion of male and female gametes
  2. sperm and egg cells in mammals
  3. offsprings inherit features from both parents
  4. the mother and father produce gametes
  5. genetic information from 2 organisms (f+m) to produce an offspring
  6. offsprings are genetically different to either parent
  7. the gametes fuse together (fertilisation) to form a cell with a full number of chromasomes
  8. in humans , each gamete contains 23 chromasomes - half the number of chromasomes in a normal cell.
• characteristics


  what an organism is like
• genes


  the sections of a chromosome that codes for a particular characteristic / protein
• alleles


  different forms of a genes eg brown / blue eyes
• genotype


  the alleles present in an organism eg BB or Bb
• phenotype


  the physical characteristic eg brown / blue eyes
• dominant


  the allele expressed in a pair of different alleles eg brown eye colour over blue. it is designated with a capital letter
• recessive


  the characteristic (feature) that does not appear when two different alleles are present. it is designated as a lower case letter
• heterozygous


  two different alleles eg Bb
• homozygous


  two alleles that are the same eg BB or bb
• genome


  the entire genetic material of an organism