Phenotypic ratios

• Autosomal linkage= when genes that are linked are found on one of the other pairs of chromosomes.
• Linked genes are inherited as one unit- there is no independent assortment during meiosis so they are inherited together.
• Recombinant offspring= they have different combinations of alleles than either parent.

  • The closer the genes are on a chromosome the less likely they are to be separated during crossing over and the fewer recombinant offspring produced
• Recombinant frequency= measure of the amount of crossing over that happens in meiosis.

  Recombinant frequency= number of recombinant offspring/total number of offspring.

  • A recombinant frequency of 50% indicates that there Is no linkage and the genes are on separate chromosomes.
  • Less than 50% indicates that there Is gene linkage and the random process of independent assortment has been hindered.
• • As the degree of crossing over reduces the recombinant frequency also gets smaller. The degree of crossing over is determined by how close the genes are on the chromosome. The closer they are the less likely they will be separated during crossing over.
• Chi-squared test

  = Measures the size of the difference between the results you actually observe and those you expected to get.

  • Helps determine whether differences in the expected and observed results are significant or not.
  • Null hypothesis= there is no significant difference between what we expect and what we observed.
  • Xsquared= sum of (observed expected)squared/expected
• If calculated Xsquared value is less then critical value (at significance 0.05) we cant reject the null hypothesis so there is no significant difference between what we observed and what we expected.

  Is calculated value is more than the critical value we reject the null hypothesis so another factor is causing the significant difference.
• Epistasis= interaction of genes at different loci.

  • Gene regulation is a form of epistasis
  • Can be dominant or recessive.
• Hypostatic= gene affected by another gene
• Epistatic= gene that effects another gene.