DNA + Genetics

• DNA-Deoxyribonucleic acid


  Molecule that contains individuals' genetic code
• DNA


  • Found in the nucleus (mainly)
  • Double helix formed into two complementary strands
• Components of nucleotides


  • Deoxyribose (sugar)
  • Phosphate
  • Base
• Bases in DNA


  • Adenine
  • Thymine
  • Cytosine
  • Guanine
• Hydrogen bonds


  Hold the two complementary strands of DNA together
• Genes


  Segments of DNA which give physical characteristics
• Chromosomes


  • Structures found in the nucleus of cells
  • Long strands of DNA wrapped around in protein
• Protein


  Made up of amino acids, functions include the control of cell and flow of material in and out of the cell
• RNA (ribonucleic acid)


  Similar to DNA, however it only consists of a single strand, the sugar molecules are ribose instead of deoxyribose, the base uracil instead of thymine
• DNA Replication


  1. Helicase unzips the DNA molecule as hydrogen bonds between the complementary bases break

  2. DNA polymerase works its way along the exposed bases and adds new nucleotides

  3. DNA ligase then comes and glues the strands back together
• After DNA replication, there are two DNA molecules, each one consisting of one strand from the original parent molecule and one newly synthesised strand
• Asexual reproduction - Many single celled organisms reproduce by mitosis (splitting, binary fission, budding, parthenogenesis), some multicellular organisms can reproduce asexually to produce clones that are genetically identical to the parent
• Sexual reproduction


  Fusion of two gametes to produce a single zygote
• Sexual reproduction


  • Introduces greater genetic variation, allows genetic recombination
  • With the exception of self-fertilising organisms (eg some plants) zygotes has gametes from two different parents
• Allele


  Different forms of a gene eg hair colour gene, I could be for brown hair and another for red
• Genotype


  Symbolic representation of the pair of alleles controlling a characteristic eg Bb
• Phenotype


  The physical characteristics eg brown eyes
• Dominant genes


  Trait that only requires one capital letter to be expressed
• Recessive genes


  Only expressed if there is no alleles for dominant trait, lower case letter
• Homozygous


  Alleles are the same a.k.a pure breeding} BB or bb
• Heterozygous


  Alleles are different} Bb
• Hybrid


  Organism containing heterozygous alleles for a characteristic
• Co-dominance (always big letter) - the heterozygous condition, where both alleles are expressed equally 
• Incomplete dominance - the heterozygous offspring show a bleding of the different alleles and therefore appear different from either parents
• Autosomal inheritance - Recessive

  • 2 unaffected individuals have an affected child
  • 2 affected cannot have an unaffected child

  examples: PKU, Tay-sachs, albinism, thalassamia cystic fibrosis
• Autosomal inheritance - Dominant

  • each affected individual has atleast one affected parent
  • each generation will have affected individuals 
  • 2 affected parents can have an unaffected child

  example: Huntingtons disease 
• Sex-linked inheritance - Recessive

  • no father-son transmission
  • predominantly male affected
  • may skip generations

  examples: colour blindness, haemophilia
• Sex determination

  • female egg carries a single X chromosome
  • male sperm carries both a X or Y chromosome (determines the sex)
  • X sperm + X egg = girl (XX)
  • Y sperm + X egg = boy (XY)
  • males cant be carriers as they dont have another X chromosome