Variation and Evolution

• Alleles


  A different version of the same gene
• Mutation


  A change in the DNA sequence
• Gamete


  Sex cell (sperm or egg)

  have 1/2 number of chromosomes as they need to make correct number when they fuse together
• Chromatids


  One of the two strands that make up a single chromosome when it is preparing to divide

  
• Phenotype


  The physical characteristics of an organism. Described by words (brown eyed)
• Genotype


  The genetic content of an organism, describing the alleles an organism has. Represented by letters (Bb)
• Homologous


  A pair of chromosomes that contain the same genes in the same locations, their alleles may differ
• Haploid


  The number of chromosomes contained in a gamete is referred to as this
• Diploid


  The number of chromosomes contained in all somatic (body) cells are referred to ad this
• Heterozygous


  When 2 different alleles are present for a gene in the genotype (Bb)
• Homozygous


  When the 2 alleles for a gene are the same in the genotype (BB)

  
  

  if both chromosomes in a pair contain the same allele of a gene, the individual is homozygous for that gene
• Dominant allele (capital letter)


  Always expressed even if only 1 copy is present (brown eyes allele = B, Bb or BB)
• Recessive allele (lowercase letter)


  2 copies needed for it to be expressed in the phenotype (blur eyes = bb, phenotype)
• Clone


  An organism that is genetically identical to its parent
• At fertilisation ..


  Gametes join to form a single body cell with new pairs of chromosomes. This cell repeatedly divides by meiosis to form many cells.
• Genetic variation examples


  Eye colour

  Hair colour

  Blood group
• Environmental variation examples


  Height

  Weight

  Teeth condition
• Polydactyl


  Genetic disorder - Having extra fingers or toes

  DOMINANT ALLELE

  can be passed on by only one parent who has the disorder
• Cystic fibrosis


  Genetic disorder - disorder of cell membranes, causes production of sticky mucus - can affect several organs; lungs, pancreas

  RECESSIVE ALLELE

  can be passed on by parents who may be carriers, and not actually have the disorder themselves
• Sickle cell anemia


  Genetic disorder - affects red blood cells, affects shape of RBC, which cannot carry O2 efficiently + may block small blood vessels->pain

  RECESSIVE ALLELE
• Downs syndrome


  Extra chromosome
• Embryo screening


  -DNA isolated from embryo cells

  -gene probe that will bind onto the gene for a specific disorder is produced

  -probe usually has fluorescent chemical attached to it

  -probe added to mixture containing DNA sample from embryo

  -UV light used to detect probe attached to gene for the disorder
• How DNA controls you?

  -genes made from DNA

  -code for proteins

  -proteins such as enzymes control reactions in body/characteristics
• asexual reproduction:


  cloning

  one parent

  no variation - genetically identical
• sexual reproduction:


  2 parents

  variety in offspring because inherit mix of genes from each parent
• causes of variation?


  - mutation of genes/DNA

  - inheriting features

  - environmental effects
• 4 methods of cloning:

  1- cuttings

  2- tissue culture

  3- embryo cloning

  4- adult cell cloning
• cuttings:


  plants

  DNA comes from adult plant

  cut piece of plant off

  sometimes use hormones and nutrient mixes
• tissue culture:


  plants

  DNA comes from adult plant

  use a cell scraped from a plant

  hormone solutions, nutrients required
• embryo cloning:


  animals

  DNA comes from embryo

  pull apart embryo into separate cells before they become specialised - these grow into clones

  need surrogate mothers
• adult cell cloning:


  animals

  DNA comes from adult animal

  fuse nucleus from one animal with empty egg - clones nucleus donor

  need surrogate mothers
• genetic engineering?


  changing DNA of an organism
• Cloning?


  making a genetically identical organism
• For questions on genetic engineering remember...

  plasmids are only used to transfer DNA to microorganisms (bacteria)

  
  

  if youre trying to engineer an animal/plant, you insert DNA directly into them when theyre still an embryo
• For ethics questions on gene technology, cover the following:


  -benefits

  -economics/costs

  -effects on environment

  -religious opposition

  -morality/ethics

  -health and safety
• difference in the characteristics of individuals of the same kind may arise due to differences in:

  - genes they've inherited (genetic causes)

  - condition in which they have developed (environmental causes)

  - a combination of the above
• Size order or gene, nucleus and chromosome?

  nucleus contains

  chromosomes carry

  genes
• genetic diagrams:


  biological models used to predict outcome of crosses

  
  

  Greger Mendel was the first to suggest separately inherited factors which we now call genes
• chromosome made up of ...

  large molecules of DNA (deoxyribonucleic acid)
• DNA contains?


  coded information that determines inherited characteristics