Reproduction, meiosis and inheritance

• What is a gamete?

  Sex cells that contain 50% of DNA e.g sperm or egg cells
• Humans reproduce by sexual reproduction which involves two gametes joining together in a process called fertilisation.
• Why is the offspring produced genetically different in sexual reproduction?

  As half of their DNA is inherited from each parent
• What is asexual reproduction?

  It only involves one parent cell and the offspring produced are genetically identical to the parent (clones)
• What are the advantages of sexual reproduction?

  • Produces genetic variation
  • Genetic variation increases the likelihood of survival in species
  • Reduces likelihood of inheriting genetic diseases
• What are the advantages of asexual reproduction?

  • Only requires one parents
  • More energy efficient
  • Faster
  • Large numbers of offspring produced very quickly
• How do plants such a strawberries and daffodils produce sexually?

  Via production of seeds leading to genetically different plants
• How do plants such as daffodils and strawberries produce asexually?

  Runners causing genetically identical plants
• How does fungi reproduce sexually?

  When conditions are not favourable which introduces genetic variation
• How does fungi reproduce asexually?

  When conditions are favourable causing them to reproduce quickly
• What is the protist that causes malaria called?

  Plasmodium
• How does plasmodium reproduce sexually?

  Inside the mosquito leading to genetic variation which increases the chance of infecting humans
• How does plasmodium reproduce asexually?

  Inside humans, reproducing very quickly to infect lots of red blood cells rapidly
• What is meiosis?


  A type of cell division that produces gametes
• Mitosis

  • Makes diploid body cells
  • Cell produces are genetically identical
  • Produces 2 cells
• Meiosis

  • Make haploid sex cells
  • Cells produced are genetically different
  • Produces 4 cells
• What happens in meiosis ?

  • Cell grows, more mitochondria and ribosomes are made
  • DNA is copied
  • Cell divides
  • Cell divides again
  • Egg or sperm cells are formed
• What is produced each time meiosis occurs?

  Four genetically different gametes are produced
• Why does each gamete contain half the number of chromosomes than a body cell?


  During fertilisation, the gamete joins together with another gamete to form a single body cell with a full set of DNA
• What is DNA


  A polymer made from repeating units called nucleotides. There are four different nucleotides. Each nucleotide is made from a phosphate group, a ribose sugar and one of the four different bases
• The DNA is made up of complimentary pairs of nucleotides. These strands are bonded together to form a double helix
• What is a chromosome?

  A long strand of DNA
• What is a gene?

  A short section of DNA that controls a characteristic. It is the instructions for making a protein
• What is an allele ?

  A different version of the same gene
• In humans there are approximately 25000 genes spread over 23 chromosome. Each body cell has two copies of each chromosome so has two copies of each gene
• What is the genome?


  All of the DNA in an organism
• Why will the genome be important in medicine?

  • To identify and test for genetic diseases
  • Potential treatment of genetic diseases
  • Migration patterns can be tracked
• A gene is a set of instructions that controls the sequence of amino acids that are joined together to make a protein
• What is a protein made of?

  Amino acids joined together
• A gene controls the order in which the ribosomes join the amino acids together
• What is a codon?

  A sequence of three bases and is the code for a particular amino acid
• What controls the order in which amino acids are assembled to produce a particular protein?

  Sequences of bases
• Stages of protein synthesis

  • DNA splits open in the nucleus and a messenger molecule leaves
  • It travels to the ribosome so it can be read
  • Inside the ribosome a carrier molecule brings the correct amino acid for each codon
  • Amino acids are added to the chain by the ribosome in the correct order
  • A protein is formed and folded into a specific 3D shape
• Why is the 3D shape of a protein important?

  It enables it to do its job as an antibody, enzyme or structural protein
• What is the name of the messenger molecule?

  mRNA
• What is a mutation?

  Error in the sequence of bases in the DNA
• Most mutations do not alter the protein that is made or only cause minor changes that do not change the appearance or the function of the protein.
• What is a substitution mutation?

  It only affects one codon so only changes one amino acid
• What is a frameshift mutation?

  Addition or deletion of a base affecting every codon after this so changes every amino acid after the mutation
• What happens when a protein has a mutation?

  No longer able to do this job: structural protein loses its strength, enzyme or antibody is no longer complimentary to the substrate or antigen