Inheritance, variation and evolution

• mitosis vs meiosis

  Mitosis: one division; forms 2 identical daughter cells; diploid cells; for growth, development and repair

  Meiosis: two divisions; forms 4 genetically different daughter cells; haploid cells; sexual reproduction (gametes)

  
• asexual reproduction


  process of reproduction involving a single parent

  ->offspring that are genetically identical to the parent (due to mitosis)

  
  

  -plants; bacteria; fungi
• sexual reproduction

  genetic variation means less susceptibility to disease, better adaption, increased survival
• sexual reproduction disadvantages

  finding a partner and mating can be difficult and time-consuming

  only half of an individual's alleles will be passed to its offspring
• asexual reproduction advantages

  less energy and time, one parent, favourable conditions
• asexual reproduction disadvantages


  no genetic variation

  -> more susceptible to disease
• structure of DNA

  double helix with a sugar-phosphate backbone -> between are the nitrogenous bases (A, T, C, G)

  
  

  each 3 letter sequence codes for an amino acid, forming a long amino acid chain-> some DNA is non-coding
• gene


  sequence of DNA that codes for a protein and so determines a characteristic
• genome


  entire genetic material for an organism
• allele

  alternative forms of a gene.
• dominant

  only one copy is needed for it to be expressed
• recessive


  2 copies are needed to be expressed; masked by a dominant allele
• homozygous

  having two identical alleles for a particular gene/characteristic
• heterozygous

  having two different alleles for a particular gene/characteristic
• genotype


  genetic makeup of an organism
• phenotype


  an organism's physical appearance or visible, shown characteristics
• polydactyly


  having more than the normal number of fingers or toes

  -> dominant allele
• cystic fibrosis


  excessive secretion of mucus and consequent vulnerability to infection

  -> recessive allele
• female chromosomes

  XX
• embryo screening

  testing embryos for genetic disorders/faulty genes and rejecting embryos that are at risk

  -> a few embryonic cells are removed and screened for defective alleles
• advantages of embryo screening

  1) It will help stop people suffering

  2) Treating disorders costs lots of money (from the government and taxpayers)
• disadvantages of embryo screening

  1) It implies that people with genetic problems are 'undesirable' - this could increase prejudice

  2) The screening may one day be used to pick the most desirable traits for their child (designer babies which is gives them an unfair advantage)

  3) Screening is expensive

  4) embryos created/destroyed so religious objections
• factors that affect phenotype

  genotype (DNA)

  environment

  -> diet, exercise, personal choice
• natural selection

  A natural process resulting in the evolution of organisms best adapted to the environment

  -> gradual changes due to mutations
• evolution

  process by which modern organisms have descended from simple ancient organisms over billions of years
• evidence for evolution

  fossils

  changes over time; how diff animals are related

  -> however fossil record is incomplete

  
  

  bacteria

  reproduce quickly so can see change
• speciation

  the formation of new and distinct species in the course of evolution

  -> geographical separation
• selective breeding

  the process of selecting a few organisms with desired traits to serve as parents of the next generation

  -> breeding for a particular characteristic
• advantages of selective breeding
• disadvantages of selective breeding

  -inbreeding leads to health problems

  - less genetic variation may mean diseases affect more organisms

  - higher chance of genetically inherited diseases

  - loss of alleles from the gene pool - can't produce new varieties in the future
• carl linnaeus

  established his classification of living things

  -> binomial naming system
• carl woese

  created the 3 domain system

  -> eukaryotes, bacteria and archaea