Year 10 Biology Revision

• DNA


  Deoxyribonucleic acid
• DNA function


  Carries the code for genetic information
• Nucleotides


  The building blocks of DNA, consisting of a sugar, a phosphate group, and a nitrogenous base
• Gene


  A segment of DNA that codes for a specific protein and contributes to a trait
• Chromosomes


  • Tightly wound package of DNA and proteins
  • Humans have 46 chromosomes (23 pairs)
  • 22 pairs of autosomes (carry genes not related to sex)
  • 1 pair of sex chromosomes
• DNA Synthesis


  1. DNA separates

  2. Complementary bases are added to exposed strands

  3. The bonds are sealed and errors are checked
• Mitosis


  • Results in two daughter cells identical to the parent cell
  • Required for growth, repair, replacement, and asexual reproduction
• Genetics


  The study of heredity and the transmission of traits from parents to offspring
• Gene


  The basic unit of heredity that is transmitted from parents to offspring and determines some characteristic of the offspring
• Inheritance


  The process by which genetic information is passed from parents to their offspring
• Alleles


  Alternative forms of a gene that occupy the same position on a chromosome and control the same characteristic
• Genotype


  The genetic makeup of an organism, consisting of the alleles present for a particular trait
• Phenotype


  The observable physical or biochemical characteristics of an organism, as determined by both genetic makeup and environmental influences
• Pure-breeding


  An organism that breeds true, producing offspring identical to the parents
• Dominant trait


  A trait that is expressed in the phenotype when only one copy of the allele is present
• Recessive trait


  A trait that is expressed in the phenotype only when two copies of the recessive allele are present
• Homozygous


  Having two identical alleles for a particular trait
• Heterozygous


  Having two different alleles for a particular trait
• In humans, the allele for brown eyes is dominant over the allele for blue eyes
• Homozygous brown = BB

  Homozygous blue = bb

  Heterozygous brown = Bb
• It is not possible to have a heterozygous blue eyed person because the allele for blue eyes is recessive
• Homozygous


  Having identical alleles for a given gene
• Heterozygous


  Having different alleles for a given gene
• Mendel's First Law (Law of Segregation)


  • Allele pairs separate during gamete formation and randomly unite at fertilisation
• Mendel's assumptions:

  • Alternative forms for genes (alleles)
  • For each trait, an organism inherits two alleles - one from each parent
  • When two alleles in a pair are different, one is dominant, one is recessive
• Dominant phenotype


  Trait expressed in both homozygous (DD) and heterozygous (Dd) individuals
• Recessive phenotype


  Trait only expressed in the homozygous recessive (dd) individual
• Tongue rolling is a dominant trait in humans. Possible genotypes of tongue rollers: TT, Tt
• Punnett Square


  • Shows all possible offspring that could result from a particular cross

  Gametes from one parent are placed at the top, gametes from the second parent are placed on the side
• Sex-linked inheritance


  Inheritance of traits controlled by genes located on the sex chromosomes (X and Y)
• Haemophilia


  • X-linked recessive trait

  Females need to receive two alleles for the recessive trait, males only need to receive one
• Pedigree


  • Diagram of how characteristics are passed from one generation to the next

  Allows us to determine the mode of inheritance and probability of an offspring for a given cross
• Mutation


  A change in the DNA sequence of a gene
• Natural selection


  The process by which certain traits become either more or less common in a population based on their relative fitness
• Evolution


  The gradual change in the characteristics of a population of organisms over successive generations, leading to the development of new species
• Selective agents


  • Light

  Temperature

  Predators

  Disease
• Light-coloured peppered moths gradually died out in the cities where pollution has changed the environment, as the dark-coloured moths were better camouflaged and had a higher survival rate.
• The rabbit population in Australia became more resistant to the myxoma virus over time because the virus initially killed 99.8% of wild rabbits, leaving only the 0.2% that were more resistant. These resistant rabbits then bred, passing on their resistance to the virus.
• Evidence for evolution


  • Fossils

  Comparative anatomy

  Genetics, protein and biochemical

  Embryology
• Fossil formation


  • Rapid burial (instant protection from elements)

  Low oxygen content (slows decomposition)

  Areas not disturbed by animals