Inheritance, Variation, and response

• Meiosis


  The formation of four non-identical cells from one cell
• Mitosis


  The formation of two identical cells from one cell
• Sexual reproduction


  1. Joining of male and female gametes, each containing genetic information from the mother or father

  2. Sperm and egg cells in animals

  3. Pollen and egg cells in flowering plants
• Gametes are formed by meiosis, as they are non identical
• Normal cell


  Has 46 chromosomes in two sets of 23 pairs, one from each parent
• Gamete


  Has 23 chromosomes, fuses in fertilisation
• The genetic information from each parent is mixed, producing variation in the offspring
• Asexual reproduction


  1. One parent with no gametes joining

  2. Happens using mitosis, where two identical cells are formed from one cell

  3. No mixing of genetic information

  4. Leads to clones, genetically identical to each other and the parent
• Meiosis


  1. Cell makes copies of chromosomes, has double genetic information

  2. Cell divides into two cells, each with half the chromosomes

  3. Cell divides again producing four gametes, each with a quarter the chromosomes

  4. Gametes are genetically different due to chromosome shuffling
• Gametes with 23 chromosomes join at fertilisation to produce a cell with 46 chromosomes
• This cell divides by mitosis to produce many copies, an embryo forms, and cells begin to differentiate
• Advantages of sexual reproduction

  • Produces variation in offspring
  • Allows selective breeding
• Advantages of asexual reproduction

  • Only one parent needed
  • Uses less energy and is faster
• Organisms using both sexual and asexual reproduction

  • Malarial parasites
  • Some fungi
  • Some plants
• DNA


  Genetic material in the nucleus, a polymer with two strands in a double helix structure
• Gene


  A small section of DNA on a chromosome that codes for a specific protein
• Genome


  All the genes coding for all the proteins within an organism
• The whole human genome has now been studied, improving understanding of genes linked to diseases, treatment of inherited disorders, and tracing human migration
• DNA structure


  1. Made of nucleotides with sugar, phosphate, and one of four organic bases

  2. Two strands with complementary base pairing (A-T, C-G)

  3. Order of bases forms a code, three bases coding for one amino acid

  4. Amino acids joined to form proteins
• Protein synthesis


  DNA in nucleus transcribed to mRNA, mRNA transported to ribosomes, amino acids brought and joined to form protein
• Mutation


  Change in DNA sequence, can insert, delete or substitute a base, affecting protein structure and function
• Most mutations do not alter the protein or only do so slightly, some can have serious effects
• Variation arises from coding DNA determining proteins and non-coding DNA controlling gene expression
• Gamete


  Reproductive cell with half the normal number of chromosomes
• Chromosome


  Structure in the nucleus made of a long strand of DNA
• Gene


  Short section of DNA coding for a protein, contributing to a characteristic
• Allele


  Different forms of the same gene, humans have two alleles per gene
• Dominant allele


  Only one is needed to be expressed and observed
• Recessive allele


  Two copies are needed to be expressed and observed
• Homozygous


  Both inherited alleles are the same
• Heterozygous


  One inherited allele is dominant, the other is recessive
• Genotype


  Combination of alleles an individual has
• Phenotype


  The physical characteristics observed in the individual
• Family trees show inheritance of phenotypes over generations
• Punnett square diagrams can be used to determine probability of offspring genotypes and phenotypes
• 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
• Family trees show the inheritance of different phenotypes over generations in the same family