A level bio-7

• Genotype


  The genetic constitution of an organism
• Phenotype


  The expression of the genes but also the interaction with the environment
• Homozygous


  Having a pair of homologous chromosomes carrying the same alleles for a single gene
• Heterozygous


  Having homologous chromosomes carrying two different alleles for a single gene
• Recessive allele


  Only expressed if there's no dominant allele present
• Dominant allele


  Always expressed
• Codominant


  Both alleles are equally dominant and expressed in the phenotype
• Multiple alleles


  More than two alleles for a single gene
• Sex linkage


  A gene whose locus is on the X chromosome
• Autosomal linkage


  Genes located on the same chromosome, not the sex chromosomes
• Epistasis


  One gene modifies or masks the expression of a different gene at a locus
• Monohybrid


  Inheritance of just one gene
• Dihybrid


  Inheritance of two genes at a time
• A genetic coding table is provided to help represent different types of inheritance in genetic crosses
• Monohybrid genetic cross


  1. Represent gene with capital letter for dominant allele, lowercase for recessive

  2. Determine probability of offspring phenotypes
• Codominant genetic cross


  1. Represent gene with base letter and superscript for alleles

  2. Determine probability of offspring phenotypes
• Multiple allele genetic cross

  1. Represent gene with base letter and superscript for alleles

  2. Determine probability of offspring phenotypes
• Sex-linked genetic cross


  1. Represent gene on X chromosome, not Y

  2. Determine probability of offspring phenotypes
• Epistasis genetic cross


  1. One gene masks expression of another

  2. Determine probability of offspring phenotypes
• Dihybrid genetic cross


  1. Represent two genes with separate letters

  2. Determine probability of offspring phenotypes
• Crossing over can result in new combinations of alleles in gametes, affecting the predicted dihybrid cross ratio
• Crossing over


  Results in new combinations of alleles in the gametes
• Autosomal linkage


  Two genes are located on the same chromosome, but not the X or Y chromosome
• Autosomal linkage


  1. Alleles for each gene are linked on the same chromosome

  2. Whole chromosome pulled to create one gamete

  3. Other chromosome pulled to create other gamete
• Autosomal linkage


  Only two types of gametes can be made - dominant alleles together, recessive alleles together
• Autosomal linkage


  Results in a 3:1 ratio instead of 9:3:3:1
• Crossing over


  Creates new combinations of gametes, leading to 4 different phenotypes
• Chi-squared


  Statistic used to investigate differences between expected and observed frequencies
• Using chi-squared


  1. State null hypothesis

  2. Convert ratio to expected frequency

  3. Calculate chi-squared value

  4. Compare to critical value
• Hardy-Weinberg principle


  Mathematical model to predict allele frequencies within a population
• Gene pool


  All the alleles of all the genes within a population at one time
• Population


  All the individuals of one species in one area at one time
• Adult frequency


  Proportion of an allele within a gene pool
• Using Hardy-Weinberg equations


  1. Identify known values

  2. Calculate p and q

  3. Use equations to find other values
• Genetic variation


  Differences in phenotype within a population due to genetic and environmental factors
• Sources of genetic variation

  • Mutations
  • Random fertilization of gametes
  • Meiosis - crossing over and independent segregation
• Natural selection


  Process where organisms with advantageous phenotypes are more likely to survive and reproduce
• Disruptive selection


  Individuals with extreme traits are more likely to survive, leading to loss of middling traits
• Speciation


  Creation of a new species due to reproductive isolation
• Allopatric speciation


  Populations become geographically isolated, accumulating genetic differences