Ecosystems

• DNA


  • It is found within the chromosomes of the cell
  • Chromosomes work to build proteins and assist in duplication or division of the cells
• DNA

  The unique structure of DNA allows it to be the hereditary molecule and allows it to store instructions for directing cell activities
• What does DNA stand for?

  Deoxyribonucleic Acid
• DNA

  • It is a long molecule made up of monomers called nucleotides
  • The backbone of DNA is formed by alternating sugar and phosphates held together by a strong bond
  • The rungs of the ladder are formed by the four nitrogen bases and are held together by weak hydrogen bonds
• Nucleotide


  The basic unit of DNA, consisting of a sugar, a phosphate, and a nitrogen base
• What structure is DNA?

  • The twisted ladder shape is called a double helix
• Name the 4 Nitrogen Bases

  • Adenine
  • Thymine
  • Cytosine
  • Guanine
• How DNA works

  1. The 4 letters of DNA make up codons

  2. These codons make up genes

  3. These genes tell cells how to make a protein that controls everything in the cell
• Genetic Variation

  Mutations in DNA produce genotypic (genetic) and phenotypic (physical) differences between individuals
• Mutations alone does not account for a significant change in the genetic variation of a population
• Name two processes that occur that occur in meisosis that are signficant

  
  

  1. Crossing over

  2. Random assortment
• Types of cell reproduction

  • Mitosis
  • Meiosis
• Metaphase I in Meiosis


  • This step is the most important for genetic variation
• Independent/Random assortment in Meiosis

  Chromosomes line up in homologous pairs (same pairs). This is significant as which pair lines up on which side is 'random' and can occur differently each time meiosis occurs.
• Crossing over in Meiosis

  When homologous chromosomes line up, they sometimes break off and swap some of their chromosome. They are swapping for the same (homologous) information, but it creates variety within the resulting chromosomes. Whether this occurs in a homologous pair or not is random.
• Fertilisation


  When fertilisation occurs, a male haploid cell (Y) combines genetic material with another haploid cell (X) to produce a diploid cell.
• Natural Selection acts on the variation that exists in species, it does not generate the variation. All variation comes from Metaphase 1 in Meiosis and fertilisation.
• Mutations can also contribute to variation in DNA but is not transmissible enough through generations of eukaryotes to be considered impactful here.
• Natural Selection


  The selection of favourable characteristics (survival of the 'fittest') by selection pressures of the surrounding environment.
• The initial population MUST have had genetic variation that contained the characteristics being selected.
• Name the two processes that occur in meiosis that are significant

  Random Assortment & Crossing Over