Interactions between unlinked genes <ul><li>Starter activity: </li></ul><ul><li>Explain the difference between ‘autosomal ...
Learning objectives <ul><li>Explain the inheritance of 2 non-interacting unlinked genes </li></ul><ul><li>Bivalent </li></...
Unlinked genes <ul><li>There are instances when a single character is influenced by 2 or more unlinked genes. Bateson and ...
Cont…. <ul><li>They realised that 2 genes were involved  </li></ul><ul><li>2 dominant alleles ‘ P ’ = pea comb and  ‘ R ’ ...
Cont… <ul><li>What was realised was that the ratio was the same as ‘Mendel’ dihybrid cross (9:3:3:1) </li></ul><ul><li>Thi...
Parents Short Long SStt ssTT Gametes St sT F1 X F1 Medium Medium SsTt SsTt Gametes ST  St  sT  st ST  St  sT  st F2
Further investigation <ul><li>Bateson and Punnet did a further investigation between 2 ‘pure-breeding’ white-flowered plan...
Cont… Flower  scent pigment   Purple   precursor   pigment Controlled by gene P Controlled by gene C Only produced if alle...
Parents Red rose Red rose SSrr ssRR Gametes Sr sR F1 X F1 Red Red SsRr SsRr Gametes SR  Sr  sR  sr SR  Sr  sR  sr F2
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Interactions Between Unlinked Genes 7

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Interactions Between Unlinked Genes 7

  1. 1. Interactions between unlinked genes <ul><li>Starter activity: </li></ul><ul><li>Explain the difference between ‘autosomal linkage’ and ‘sex linkage’ </li></ul><ul><li>Autosomal Linkage refers to genes being on the same chromosome.  These genes tend to show up together in the same combinations in the offspring </li></ul><ul><li>Sex linkage If a gene is located on the X chromosome, the male has the problem that he does not have a homologue for this chromosome. He has a Y chromosome that doesn't have the same information on it as the X. Therefore, whatever allele he inherits from his mother's X chromosome, he expresses that allele </li></ul>
  2. 2. Learning objectives <ul><li>Explain the inheritance of 2 non-interacting unlinked genes </li></ul><ul><li>Bivalent </li></ul><ul><li>Pair of two homologous chromosomes formed by synapsis during the early stages of meiosis. </li></ul><ul><li>Bivalents separate into half bivalents during first meiotic division. </li></ul><ul><li>Shape of bivalent will depend upon: </li></ul><ul><li>number of chiasmata </li></ul><ul><li>position of chiasmata </li></ul><ul><li>size of chromosome </li></ul><ul><li>                                                                                                                                              </li></ul>
  3. 3. Unlinked genes <ul><li>There are instances when a single character is influenced by 2 or more unlinked genes. Bateson and Punnet did research of unlinked genes such as the ‘combs’ in poultry. </li></ul><ul><li>There are 2 types of combs (‘pea’ combs and ‘rose’ combs) </li></ul><ul><li>The F1 were ‘true’ bred </li></ul><ul><li>Produced ‘walnut’ comb and ‘single’ comb </li></ul><ul><li>The phenotype occurred in the ratio of 9:3:3:1 </li></ul>
  4. 4. Cont…. <ul><li>They realised that 2 genes were involved </li></ul><ul><li>2 dominant alleles ‘ P ’ = pea comb and ‘ R ’ = rose comb </li></ul><ul><li>So the genotypes of the parents in the original test cross (PPrr (pea comb) and ppRR (rose comb) </li></ul><ul><li>F1 genotype was PpRr interacting to give a ‘walnut’ comb </li></ul><ul><li>F2 genotype with no dominant alleles pprr to give a ‘single’ comb </li></ul>
  5. 5. Cont… <ul><li>What was realised was that the ratio was the same as ‘Mendel’ dihybrid cross (9:3:3:1) </li></ul><ul><li>This indicated that the 2 genes were inherited independently </li></ul><ul><li>‘walnut’ and ‘single’ combs were new forms of character due to the interaction of the genes and were not considered to be recombinants </li></ul><ul><li>There are examples gene interaction where the ratio is different </li></ul>
  6. 6. Parents Short Long SStt ssTT Gametes St sT F1 X F1 Medium Medium SsTt SsTt Gametes ST St sT st ST St sT st F2
  7. 7. Further investigation <ul><li>Bateson and Punnet did a further investigation between 2 ‘pure-breeding’ white-flowered plants sweet pea plants. This produced offspring with ‘purple’ flowers. The purple-flowered plants were allowed to self-pollinate to which the resulting progeny were (purple 9 : white 7) ratio. </li></ul><ul><li>This suggested that one gene (C) controlled the scent of the pigment and the other gene (P) controlled the conversion to its purple form </li></ul><ul><li>For the purple colour to develop, both genes must be present ( C, P) </li></ul><ul><li>For this to occur both white-flowered plants must be homozygous dominant for one of the genes, for the offspring to be purple </li></ul>
  8. 8. Cont… Flower scent pigment Purple precursor pigment Controlled by gene P Controlled by gene C Only produced if allele P present Only produced If both alleles P and C present
  9. 9. Parents Red rose Red rose SSrr ssRR Gametes Sr sR F1 X F1 Red Red SsRr SsRr Gametes SR Sr sR sr SR Sr sR sr F2

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