Topic 6 - Inheritance, Variation and Evolution

• Meiosis - the process by which gametes are made. Genetically different from the parent cells
• Meiosis:

  Chromosomes in diploid cells (23 pairs) copied -> similar chromosomes pair up and genes are swapped between them -> cell divides to produce two diploid cells -> these divide again to produce 4 haploid cells (gametes)
• Most animals reproduce sexually while plant can reproduce sexually (pollen and egg) and asexually
• Asexual reproduction happens by mitosis so the offspring are genetically identical
• Sexual advantage: offspring can become better adapted to their environment

  Asexual advantage: only one parent is needed to reproduce
• Malaria parasites and some fungi can do both
• Genome - the entire genetic code in an organism
• DNA - double helix polymer that stores genetic code
• Gene - portion of DNA that codes for a protein - mapping these allows us to identity causes of disorders
• Genotype - an organism's specific genetic code
• Phenotype - how a genotype is expressed in physical characteristics
• Monomers/Nucleotides/Bases are made from a sugar/phosphate group
• Bases: A+T, C+G (Apple + Tree and Car + Garage). Every three bases code for an amino acid
• Protein synthesis:

  Code is copied by mRNA (transcription), taken to ribosome which assembles amino acids into polypeptides then proteins (translation) that are then folded into shape.
• Mutations can result in wrong proteins being synthesised
• Characteristics are determined by the type and quantity of proteins synthesised. Some are controlled by one gene however most are a result of two or more genes interacting. Different versions of the same genes are called Alleles.
• Dominant alleles are expressed even when a genotype contains a recessive allele. There must be no dominant allele in order for a recessive allele to be expressed in the phenotype.
• BB and bb are homozygous alleles whereas Bb is heterozygous
• Homozygous = one type of allele
• Heterozygous = two types of allele
• Polydactyly is caused by a dominant allele. Cystic fibrosis is due to a recessive allele
• Females have XX chromosomes while males have XY chromosomes
• Variation is a result of both genetic and environmental factors
• Darwin's theory of evolution:

  • Random mutations result in variation
  • Some organisms better adapted to environment
  • These compete (survival of the fittest)
  • Those better adapted ar more likely to survive - overtime these desirable characteristics are more pronounced
• Lamark's theory of evolution:

  • Mutations/adaptations are a result of environment affecting characteristics inherited by offspring and are not random
• Antibiotic-resistant bacteria are used as evidence for Darwin's theory. If not all bacteria are killed, those most resistant will reproduce. This is why you must complete the full course of antibiotics
• Species = a group of organisms that can breed to produce fertile offspring
• Selective breeding = breeding organisms that have desired characteristics to produce offspring in which they are more pronounced
• Genetic engineering - the insertion of a gene into an organism's genome so it synthesised a specific protein to achieve a desired characteristic
• Examples of GM:

  • Insulin-producing bacteria
  • Creating GM crops like golden rice that produces Vitamin A
  • Disease resistant crops
• The desired gene is cut from another organism's DNA using enzymes -> gene inserted into a vector e.g bacteria, plasmid or virus -> vector inserts gene into cells of another organism in early development -> organism develops with desired characteristic due to cells synthesising that specific protein
• Fossils - the decayed remains of organisms
• Fossils that look like bones are actually bones that have been replaced with minerals
• Some fossils can still have soft organic tissue if the conditions for decay are not present
• Footprints that have hardened in mud are considered fossils, as are other traces of organisms left behind
• Cloning = producing genetically identical organisms
• Can clone plants using cutting or tissue cultures
• Cloning animals:

  The cells resulting from fertilising can be separated to produce identical offspring
• Cloning process:

  The nucleus is taken from the skin cell of an organism to be cloned -> nucleus is inserted into an egg cell -> electric shock causes the egg to split and develop ->developing cell is inserted into a surrogate mother -> clone is born
• Linnaeus's Taxonomy Classification:

  Kingdom (King)

  Phylum (Philip)

  Class (Came)

  Order (Over)

  Family (For)

  Genus (Good)

  Species (Soup)