Unit 7 bio

• Genotype


  The genetic constitution of an organism
• Phenotype


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


  When you have a pair of homologous chromosomes carrying the same alleles for a single gene
• Heterozygous


  When you have the 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


  The 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 with different types of inheritance
• Monohybrid example - Cystic fibrosis

  • Cystic fibrosis is caused by a recessive allele
  • Parents are heterozygous
• Multiple alleles and codominance example - Blood groups

  • Blood group A has dominant A allele or recessive O allele
  • Blood group B has dominant B allele or recessive O allele
  • Blood group AB has both dominant A and B alleles
  • Blood group O has two recessive O alleles
• Sex linkage example - Colour blindness

  • Colour blindness is caused by a recessive allele on the X chromosome
  • Non-colour blind male reproduces with female carrier
• Epistasis example - Labrador coat colour

  • Gene 1 controls whether pigment will be produced (dominant allele) or not (recessive allele)
  • Gene 2 controls the colour of the pigment (dominant black, recessive brown)
• Dihybrid cross


  1. Consider inheritance of two genes at the same time

  2. Need parental phenotypes and genotypes

  3. Work out gametes

  4. Punnett square to get offspring genotypes and phenotypes

  5. Determine the ratio
• Autosomal linkage


  Two genes located on the same chromosome, not sex chromosomes
• Crossing over results in new combinations of alleles in the gametes, affecting the predicted ratio
• Crossing over


  Results in new combinations of alleles in the gametes, so the predicted gametes in the Punnett square may differ
• 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. Have to be inherited together

  3. Whole chromosome pulled to create one gamete

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


  Only two types of gametes possible: dominant alleles or recessive alleles
• Autosomal linkage


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


  Creates new combinations of gametes, resulting in more than 2 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

  5. Determine if significant difference
• Hardy-Weinberg principle


  Mathematical model to predict allele frequencies in 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
• p


  Frequency of the dominant allele
• q


  Frequency of the recessive allele
• p^2


  Frequency of the homozygous dominant genotype
• 2pq


  Frequency of the heterozygous genotype
• q^2


  Frequency of the homozygous recessive genotype
• Genetic variation is due to mutations, random fertilization, and meiotic processes
• Natural selection


  • Predation
  • Disease
  • Competition