Variation & Evolution

• taxonomy is the study of classification
• the unit of classification is the species
• species is a group of similar organisms that are capable of interbreeding and produce fertile offspring
• heredity is the passing on of features from parent to offspring by means of genes
• acquired variations are not inherited or controlled by genes they are learned or developed
• inherited variations are controlled by genes (DNA)
• variation is the individual differences between members of the same species
• inherited variations are caused by

  • sexual reproduction
  • mutations
• sexual reproduction cause the majority of inherited variations because of 2 reasons

  • independent assortment (at gamete formation)
  • crossing over (during meiosis)
• mutation is a change in the amount or structure of DNA
• mutations may be harmful as it could case the rate of mitosis to increase resulting in a tumour
• beneficial mutation are the source of evolution
• causes of mutations

  DNA doesn't repair itself properly

  DNA doesn't produce exact copies of itself
• mutagens are outside agents that cause mutations
• mutagens speed up the rate of spontaneous mutations
• mutagen that causes cancer = carcinogen
• 3 types of mutagens

  radiation - X-rays

  chemicals - pesticides

  viruses
• types of mutations

  gene mutations

  chromosome
• gene mutations are changes in a single gene
• sickle cell anaemia

  mutation in the gene for haemoglobin

  mutated gene = recessive allele

  haemoglobin produced is insoluble

  this causes the RBC to have a sickle shape

  RBC clump & breakdown
• effects of sickle cell anaemia

  paleness

  weakness

  heart failure
• chromosome mutations are large changes in the number or structure of chromosomes
• chromosome mutation example

  Down's syndrome

  caused by 1 extra chromosome (2n=47)

  chromosome no21 has 3 copies
• evolution is how living things change genetically to produce new forms of life over long periods of time
• who came up with the theory of natural selection

  Charles Darwin & Alfred Russel Wallace
• theory of natural selections 3 observations

  overbreeding

  populations remain constant

  inherited variations occur in populations
• theory of natural selection conclusions

  there is a struggle for existence

  natural selection
• natural selection is the process by which particular traits become more common in a population due to that trait being advantageous to the species
• speciation is the production of a new species as a result of evolution
• Theory of Natural Selection

  natural selection happens because individuals of a species have inherited differences or variations

  this results in different abilities to survive and reproduce

  natural selection occurs when the environment acts on the inherited differences between organisms of the same species.

  natural selection results in organisms of a species becoming better adapted to their environment
• evidence for evolution

  the fossil record

  comparative anatomy

  embryo studies
• paleontology is the study of fossils
• a fossil is the preserved remains/evidence of something that lived a long time ago
• example of fossils


  shells

  bones

  footprints

  teeth
• fossil evidence for evolution

  fossils can be aged (using radiocarbon dating)

  fossils show change