inheritance

• Gametes


  sex cells
• Gametes are made by

  Meiosis
• Sexual reproduction


  -Involves the fusion of Male and female gametes (fertilisation)

  -mixing of genetic information so we can see variation in offspring
• Asexual reproduction


  -one parent

  -does not involve gametes and no mixing of genetic information

  -offspring are identical

  -only involves mitosis
• Clones


  identical genetic copies
• Meiosis


  -all chromosomes are copied

  -cell divides into two and then one more time, forming gametes

  -in the gametes the chromosomes are not in pairs so they have been halved

  -produces four gametes from one cell, all genetically different
• Meiosis takes place


  In reproductive organs, ovaries and testes
• Fertilisation


  Fusing of a male sex cell with a female sex cell
• Advantages of sexual reproduction

  -variation which gives the species more chance of survival because of natural selection (some will survive and reproduce)
• Advantages of asexual reproduction

  -no need to find a mate

  -more efficient and faster

  -allows an organism to produce many genetically identical offspring rapidly
• Disadvantages of asexual reproduction

  -no genetic variation so if conditions become unfavourable they all die
• Chromosomes contain


  DNA
• Structure of DNA


  double helix, each strand is a polymer
• DNA contains


  genes
• Each gene


  encodes for a specific sequence of amino acids to make a unique protein
• Genome


  all of an organism's genetic material
• Benefits of understanding the human genome

  -help us to search for genes that are linked to a disease like cancer

  -help us treat inherited disorders like CF

  -trace human migration patterns to discover ancestors
• nucleotides


  contain a phosphate group, sugar molecule, base

  
• Base pairs


  A-T

  C-G
• What does the order of amino acids determine?

  the shape of the protein
• What does the shape of a protein determine?

  its function
• Examples of proteins

  enzymes and antibodies
• How is the order of amino acids determined?

  by a sequence of bases in the gene for that protein
• Gregor Mendel


  investigated products of sexual reproduction on pea plants
• What did Mendel discover?

  -he discovered that characteristics are determined by 'units' that are inherited and do not blend together

  -scientists discovered that the 'units' he discovered acted similarly to chromosomes and they were later named genes
• Why was Mendel's discovery not recognised in his lifetime?

  -he was a monk not a scientist

  -he did not publish his work in a well known book
• Alleles


  Versions of a gene
• Genotype


  genetic makeup of an organism
• Homozygous


  Having two identical alleles for a particular gene
• Heterozygous


  Having two different alleles for a trait
• Phenotype


  An organism's physical appearance, or visible traits.
• Recessive

  A recessive allele will only show in the phenotype if two copies are present
• Dominant


  A dominant allele will show in the phenotype even if there is only one copy present
• Cystic fibrosis


  -disorder of cell membranes

  -controlled by a single gene

  -defective allele is recessive

  -affects respiratory and digestive system
• What is a carrier

  heterozygous genotype that carries recessive trait but doesn't express it
• Polydactyly


  -extra fingers or toes

  -caused by a dominant allele
• You cannot be a carrier of

  A dominant allele because you will have the phenotype
• Embryo screening


  A process of testing embryos for genetic disorders and rejecting embryos that are at risk
• Issues around embryo screening

  -expensive

  -some healthy embryos are destroyed
• Gene therapy


  The insertion of working copies of a gene into the cells of a person with a genetic disorder in an attempt to correct the disorder