Populations and evolution

• What is a species?

  a group of similar organisms that can reproduce to give fertile offspring.
• Why can two different species not produce fertile offspring.

  Organisms of the same species have the same number of chromosomes, so when organisms with a different number of chromosomes reproduce the zygote will have an odd number of chromosomes which is not viable.
• What are populations?

  group of organisms of the same species occupying a particular space at a particular time.
• What is a gene pool?

  the collection of genes within a population at a particular time. This takes into account the alleles of the genes.
• What is allele frequency?

  how often different alleles occur in the gene pool.
• How do new species form?

  Overtime the gene pool of a species population changes due to natural selection.
• What is phenotype frequency?

  number of individuals in a population that have a specific observable trait.
• How do you calculate phenotype frequency?

  (total individuals with phenotype / total individuals in population) x 100
• What does the Hardy-Weinberg principle state?

  If certain conditions are met, the allele frequencies of a gene within a population will not change from one generation to the next.
• What conditions needs to be met for the hardy Weinberg principle to be true?

  Diploid organisms.

  
  

  Only reproduce sexually.

  
  

  No overlap with generations i.e. parents do not reproduce with their offspring.

  
  

  Mating is random.

  
  

  The population is large.

  
  

  There is no migration, mutation, or selection.

  
  

  Allele frequency's are equal in both sets.
• How do you work out allele frequency?

  P = frequency of dominant allele

  Q = frequency of recessive allele

  P^2 = the frequency of the homozygous dominant genotype

  2PQ. = the frequency of the heterozygous genotype

  Q^2 = the frequency of the homozygous recessive allele

  
  

  P + Q = 1

  
  

  P^2 + Q^2 + 2PQ = 1