B5

• Gamete


  An organism's reproductive cell (egg in female and sperm in males), which has half the number of chromosomes (23)
• Chromosome


  A structure found in the nucleus which is made up of a long strand of DNA
• Gene


  A short section of DNA that codes for a protein, and therefore contribute to a characteristic
• Gamete


  An organism's reproductive cell (egg in female and sperm in males), which has half the number of chromosomes (23)
• Chromosome


  A structure found in the nucleus which is made up of a long strand of DNA
• Gene


  A short section of DNA that codes for a protein, and therefore contribute to a characteristic
• Allele/variant


  The different forms of the gene - humans have two alleles for each gene as they inherit one from each parent
• Dominant allele


  Only one (out of the two alleles) is needed for it to be expressed and for the corresponding phenotype to be observed
• Recessive allele


  Two copies are needed for it to be expressed and for the corresponding the phenotype to be observed
• Homozygous


  When both inherited alleles are the same (i.e. two dominant alleles or two recessive alleles)
• Heterozygous


  When one of the inherited alleles is dominant and the other is recessive
• Genotype


  The combination of alleles an individual has, e.g. Aa
• Phenotype


  The physical characteristics that are observed in the individual, e.g. eye colour
• Genome


  The genetic information of that organism
• Genetic information and its interaction with the environment


  • Influence how genetic traits are presented, i.e. the phenotype
• Continuous variation


  Variation in a characteristic that occurs in a range, such as height
• Discontinuous variation


  Variation in a characteristic that occurs in distinct categories, such as eye colour
• The human genome has been studied, which has improved our understanding of the genes linked to different types of disease, the treatment of inherited disorders and has helped in tracing human migration patterns from the past
• Mutation


  Causes all variants (alleles)
• Most mutations have no effect on the phenotype, as most of DNA is non-coding and therefore does not cause a change in any proteins
• Some mutations do have a small influence on phenotype and very few can completely change the phenotype if they are in coding regions
• Coding region


  Part of DNA that codes for a protein
• Non-coding region


  Part of DNA that does not code for a protein
• Protein synthesis


  1. DNA contains the genetic code

  2. mRNA nucleotides match to complementary base on DNA strand

  3. mRNA strand is created

  4. mRNA moves to cytoplasm and onto ribosomes

  5. Bases on mRNA are read in threes to code for amino acids

  6. Amino acids are brought to ribosomes by carrier molecules

  7. Amino acids connect to form a protein

  8. Protein folds to form 3D structure
• Advantages of sexual reproduction

  • Produces variation in offspring
  • Decreases chance of whole species becoming extinct
• Advantages of asexual reproduction

  • Only one parent is needed
  • Allows selective breeding
  • Uses less energy and is faster as organisms do not need to find a mate
  • In favorable conditions lots of identical offspring can be produced
• Meiosis


  1. Cell makes copies of chromosomes

  2. Cell divides into two cells with half the amount of chromosomes

  3. Each cell divides into two again to produce four genetically different cells with 23 chromosomes each
• Diploid


  Cell has double the amount of genetic information
• Haploid

  Cell has half the normal amount of chromosomes (23)
• Punnett square diagram


  Used to show the probability of offspring having certain genotypes and phenotypes
• Most phenotypic features are the result of many different genes interacting rather than a single gene inheritance
• Uppercase letters


  Represent dominant characteristics
• Lowercase letters


  Represent recessive characteristics
• Sex determining genes


  Located on the 23rd chromosome pair
• X chromosome


  Females have two, and pass on X chromosomes in their eggs
• Y chromosome


  Males have one, and can pass on X or Y chromosomes in their sperm
• There is a 50% chance of babies being born as either a boy or a girl
• Gregor Mendel's conclusions from breeding experiments on pea plants


  • Offspring inherit 'hereditary units' from each parent
  • One unit is received from each parent
  • Units can be dominant or recessive, and cannot be mixed together
• Mendel was not recognised till after his death as genes and chromosomes were not yet discovered, so people could not understand his work
• In the late 19th century chromosomes as a part of cell division were observed