B6- GENTICS

• Meiosis


  The process by which gametes (sex cells) are made, involving the division of a diploid cell to produce four haploid cells
• Meiosis


  1. Chromosomes are copied and similar chromosomes pair up

  2. Genes are swapped between them

  3. Cell divides to make two diploid cells

  4. Cells divide again to make four haploid cells
• Variation in offspring


  Occurs through the process of meiosis and the fusion of gametes
• Asexual reproduction


  Daughter cells are genetically identical to the parent, resulting in clones
• Advantages of sexual reproduction

  • Variation occurs, which can result in organisms becoming better suited to their environment and more likely to survive
• Advantages of asexual reproduction

  • Only one parent is needed, so a plant on its own can still reproduce to ensure the species survives
• Genome


  The complete set of genetic material in an organism, stored in DNA
• Gene


  A section of DNA that codes for a specific protein
• The Human Genome Project completed its initial goal in 2003, mapping out what every gene is responsible for coding
• Genotype


  The genetic code stored in an organism's DNA
• Phenotype


  How an organism's genotype is expressed in its characteristics and physiology
• Mutations


  Changes to a gene that can result in a protein being synthesized that doesn't do its intended job
• Alleles


  Different versions of the same gene
• Dominant allele


  An allele that results in a characteristic being expressed even if another recessive allele is present
• Recessive allele


  An allele that is only expressed when there is no dominant allele present
• Homozygous


  Having two of the same type of allele
• Heterozygous


  Having two different types of alleles
• Punnett square


  Used to predict the probability of certain phenotypes occurring in offspring
• Dominant alleles can result in disorders being inherited, like polydactyly (extra fingers/toes), while recessive alleles can result in disorders like cystic fibrosis
• Sex chromosomes

  XX = female, XY = male
• Charles Darwin's theory of evolution states that random variation in offspring will result in some being better suited to their environment and more likely to survive and reproduce
• Lamarck's theory of evolution asserted that adaptation and variation are guided by DNA in response to a changing environment
• Bacterial resistance to antibiotics is evidence of evolution, as resistant bacteria are selected for and reproduce
• Species


  Organisms that can produce fertile offspring are considered the same species
• Selective breeding


  Breeding organisms with desired characteristics to enhance those traits
• Genetic modification


  Directly altering an organism's DNA to introduce desired characteristics
• Genetic engineering- process


  1. Gene is chemically cut from organism with desired trait

  2. Gene inserted into vector like bacteria or virus

  3. Vector inserts gene into target organism
• Fossils


  Remains or traces of organisms that died a long time ago, preserved in rock or other materials
• Levels of classification


  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• The three domains of life are Archaea, Bacteria, and Eukarya
• Archaea are often found in extreme environments and are called extremophiles
• Mitosis


  A type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus
• Polydactyly


  Genetic disorder where a person has extra fingers or toes
• Embryo screening


  1. Remove a cell from each embryo

  2. Analyse the genes

  3. Detect genetic disorders
• It's possible to get DNA from an embryo in the womb and test that for disorders
• Concerns surrounding embryo screening

  • Ethical
  • Social
  • Economic
• Embryos with 'bad' alleles

  Would be destroyed
• Womb-screening


  Could lead to the decision to terminate the pregnancy
• Arguments against embryonic screening

  • It implies that people with genetic problems are 'undesirable' - this could increase prejudice
  • There may come a point where everyone wants to screen their embryos so they can pick the most 'desirable' one
  • Screening is expensive
• Arguments for embryonic screening

  • It will help to stop people suffering
  • Treating disorders costs the Government (and the taxpayers) a lot of money
  • There are laws to stop it going too far