Inheritance , variation and evolution

• Meiosis - leads to non identical cells being formed

  Mitosis - leads to identical cells being formed
• Sexual reproduction - The process of producing offspring through fusion of gametes from two parents.
• Asexual reproduction is when one parent produces offspring with the same genetic makeup as itself
• Meiosis halves the number of chromosomes in gametes and fertilisation restore the full number of chromosomes
• Cells in reproductive organs divide by meiosis to form gametes
• When a cell divides to form gametes

  • Copy of the genetic information are made
  • the cell divides twice to form four gametes , each with a single set of chromosomes
  • all gametes are genetically different from each other
• Gametes join at fertilisation to restore the normal number of chromosome. The new cell divides by mitosis
• DNA - a polymer made up of two strands forming a double helix & dna is contained in structurea called chromosome
• Genome - the entire set of genetic material in an organism
• Genome

  • help to identify gene disease
  • helps doctors to find effective treatment for us
  • trace the migration of our ancestors
• gene - small section of DNA that codes for a particular type of protein
• Each gene may have different forms called alleles
• Some characteristics are controlled by a single gene , such as fur colour in cats
• A dominant allele is always expressed , even if only one copy is present
• A recessive allele is only expressed if two copies are present
• Genotype - tells us the alleles present for example Ee
• Phenotype - tells us the characteristics caused by the persons alleles
• Homozygous - Having two copies of the same alleles of a particular gene, e.g. BB
• Heterozygous - Having two different alleles for a particular gene e.g Bb
• Polydactyly - having extra fingers or toes & is caused by a dominant allele
• cystic fibrosis - a disorder of cell membrane & is caused by a recessive allele
• Embryo screening - a test that can be done on embryos to see if they have a genetic disorder
• Issues around embryo screening

  • it’s expensive some believe the money should be put elsewhere in healthcare
  • embryos are destroyed and some think this is morally wrong
• 23 pairs of chromosome in which 22 pairs control characteristics , but only one of the pairs carry the genes that determine sex
• In females sex chromosome are the same ( XX)
• In males the chromosomes are different ( XY)
• Variation - all the different characteristics of individuals in a population
• Variation may be due to

  • the genes they inherited (genetic causes)
  • the conditions in which they have develop(environmental causes)
  • a combination of genes and the environment
• All variants arise from mutations and that : most have no effect on the phenotype ; some influence the phenotype ; very few determine pheotype
• Mutations - changes in the DNA sequence of an organism that can lead to changes in the phenotype. ( characteristics )
• Mutations occur continuously. Very rarely a mutation leads to a new phenotype
• Evolution - the process of mutation & natural selection which leads to a change in species over time to suit a particular environment
• Explain how evolution occurs through natural selection of variants that gives rise to phenotypes best suited to their environment

  If two populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring they have formed two new species
• Selective breeding - is the process by which humans breed plants & animals for particular genetic characteristics
• Pros of selective breeding

  • animals which produce more meat or milk
  • Large or unusual flowers
  • domestic dogs with a gentle nature
  • diseases resistance in crops
• Selective breeding cons

  • inbreeding in which some breeds can be prone to disease or inherited defects
• Genetic engineering- the process of modifying the genetic material of an organism to produce a desired chartecterisitc
• Plant crops have been genetically engineered to be resistant to diseases & produce bigger fruit
• Bacteria cells have been gentically engineered to produce useful substances such as human insulin to treat diabetes
• genetically modified - crops in which have had there genes modified by genetic engineering