B3 GENETICS

• Meiosis

  Produces 4 genetically different haploid cells
• Haploid cell

  Has 23 chromosomes
• DNA structure

  A polymer made up of two strands coiled to form a double helix
• DNA strands

  Made from a series of complementary base pairs
• DNA strands held together by

  Weak hydrogen bonds
• Cytosine (C) base pair

  Guanine (G)
• Guanine (G) base pair


  Cytosine (C)
• Adenine (A) base pair

  Thymine (T)
• Thymine (T) base pair

  Adenine (A)
• Genome

  All the genetic material of an organism
• Gene

  A section of a DNA molecule that codes for a specific protein
• DNA extraction

  1. Crush fruit to break down cell walls

  2. Add detergent to break down cell membrane

  3. Add salt to clump DNA together

  4. Add protease to break down proteins and destroy enzymes

  5. Heat and filter

  6. Pour ice cold ethanol into filtrate to precipitate DNA
• Protease is added when extracting DNA to break down proteins in the nuclear membrane and destroy enzymes that may break down the DNA
• Ice cold ethanol is used in the extraction of DNA to precipitate the DNA (DNA is insoluble in ethanol)
• Filtration is used in the extraction of DNA to remove insoluble material
• Allele

  A version of a gene
• Types of allele

  Dominant and recessive
• Homozygous

  There are two copies of the same allele
• Heterozygous

  There is one dominant and one recessive allele
• Phenotype

  The physical characteristics of an individual
• Gamete

  A sex cell that has a haploid nucleus
• Zygote


  A fertilised egg cell
• Female genotype

  XX
• Male genotype


  XY
• Types of variation that influence phenotype

  • Genetic variation
  • Environmental variation
• Benefits of discovering the sequence of bases for all plants and animals include identifying useful genes, tracking evolution, understanding diseases, discovering new medicines, and identifying sequences that allow organisms to cope with environmental change
• The Human Genome Project has contributed to advances in medicine by identifying genes on human chromosomes, allowing faulty genes to be identified, enabling people to be tested for genetic disorders, enabling the development of gene therapy, and allowing personalised medication and counselling to be given
• Genetic variation is caused by mutation and sexual reproduction
• Environmental variation is caused by an organism's environment
• Most genetic mutations do not affect the phenotype, as some may have a small effect and rarely a single mutation will significantly affect the phenotype
• Cystic fibrosis can reduce body mass because the mucus blocks the pancreatic duct = preventing enzymes being released