Topic 6

• What is meiosis?


  The process in which gametes are made - genetically different from each parent cells.

  • chromosomes in diploid cell pair up and genes swap between them
  • cell divides to produce two diploid cells
  • these divide again to produce 4 diploid cells
• What is asexual reproduction?

  A type of reproduction that happens via mitosis meaning offspring cells will be identical

  Advantages: Only one organism needed to reproduce, quick and time efficient

  Disadvantages: One disease can wipe out entire population due to everything being identical
• What is sexual reproduction?

  A type of reproduction where gametes meet to form a zygote. The offspring is unique and different from parents.

  Advantages: offspring can become better adapted to environment and more variation

  Disadvantages: Two parents are needed and time consuming
• What is a genome?


  A genome is the complete set of genetic material (DNA or RNA) present in an organism.

  Advantages: has allowed scientists to better understand cause of diseases and has prevented and cured many diseases

  Disadvantages: some may not want to find out about their diseases
• What is DNA?


  A double helix polymer that stores genetic code and is found in chromosomes
• What is a gene?


  A portion of DNA that codes for a protein
• What is a genotype?


  An organism's specific genetic code
• What is a phenotype?


  The physical expression of genes
• What are the complimentary base pairs?

  Adenine-Thymine, Guanine-Cytosine

  A + T, C + G
• What is protein synthesis?

  • code is copied by mRNA
  • then taken to ribosomes which assemble amino acids to polypeptides then proteins (translation) that are folded into shape

  Mutations can result in the wrong proteins being synthesised
• What are alleles?


  Different versions of the same gene
• What are dominant alleles?

  Alleles that are always expressed regardless of if recessive alleles are present. It's represented by capital letters such a "B"
• What are recessive alleles?


  Alleles that are only expressed when paired with another recessive allele, its represented by a lowercase letter such as "b"
• What does it mean by homozygous alleles?


  Identical alleles.
• What does it mean by heterozygous alleles?

  Different versions of a gene.
• What is polydactyly and cystic fibrosis caused by?

  Polydactyly - dominant allele

  Cystic fibrosis - recessive allele
• How are female and male chromosomes portrayed?

  XX chromosomes are female, while males have XY

  (in a Punnett square, the mum goes on the bottom, left side, whilst the dad is on the top)
• What is variation?


  Differences between species
• What did Gregor Mendel find out?

  He discovered the inheritance of characteristics determined by genes via experimenting with pea plants
• Why was Mendel's work not accepted at first?

  • Other's thought he went against God
  • Not enough evidence to prove it
• How did microscopes and chromosomes prove his work?

  Microscopes allowed scientists after Mendel's death to study chromosomes which showed how Mendel's laws to behaviour of chromosomes during cell division were
• What is evolution?


  Change in characteristics of a population over time.
• What is natural selection?

  The name of Darwin's theory in which he believed that evolution occured.

  It had five stages:

  • Variation caused by mutations
  • Competition
  • Survival of fittest
  • Breed
  • Genes get passed on
• What is the theory of evolution by natural selection?

  The theory of evolution by natural selection states that all species of living things evolved from the same common ancestor from billions of years ago
• Who was Charles Darwin?

  Charles Darwin was a British naturalist and biologist who proposed the theory of evolution through natural selection.
• What was Lamarck's theory?

  Inheritance of acquired characteristics which was proved wrong by fossils
• What is speciation?


  Where populations have become so different from each other that they can no longer interbreed to produce fertile offspring

  It consisted of 5 stages:

  • members of species seperated
  • populations are isolated
  • variation within isolated populations
  • those best suited to their environment survive till adulthood, reproduce and pass on their own genes
  • over a long period of time a new species results
• Who was Alfred Russel Wallace?

  A British naturalist and explorer who independently developed the theory of evolution by natural selection. He also helped Charles Darwin to publish his findings
• What are fossils?


  Remains of organisms from millions of years ago
• What are the problems with fossil records?

  • most bodies don't form fossils
  • some fossils have been destroyed
  • some fossils have not been found yet
  • some fossils are buried too deep
  • fossil record is incomplete
• How are fossils formed?

  • Mineralisation is when minerals seep into the structure of the organism replacing the bones
  • Amber fossils occur when amber, a tree resin, traps small insects. The resin hardens, preserving the trapped organism
  • Some organisms become trapped in ice which get preserved for millions of years