PEDIGREES

=Pedigrees= [image:http://i.imgur.com/kwM0enP.png] In a pedigree, males are represented by squares, and females with circles. [image:http://i.imgur.com/uLzpKFO.png] Affected individuals (those with a disease or characteristic of interest) are shaded. [image:http://i.imgur.com/gL73hSe.png] When two individuals have a child they are shown as follows [image:http://i.imgur.com/zqN5VAM.png] Multiple children are shown as follows Successive generations are shown as follows [image:http://i.imgur.com/bOytO3Z.png] For a pedigree to be of any use, we must first decide if the condition is dominant or recessive. If the condition is dominant: *Affected individuals = AA or Aa *Unaffected individuals = aa *Affected individuals have always inherited the dominant allele (A) from at least one of their parents (who therefore must also be affected). Therefor the dominant condition should be seen in every generation. Two affected individuals (if they were Aa) could also produce an unaffected child (aa) If the condition is recessive: *Affected individuals = aa *Unaffected individuals = AA or Aa *Affected individuals (aa) often have two unaffected parents (Aa) ==Recessive Disorder== [image:http://i.imgur.com/0tLr0kS.png] This condition must be recessive because the condition has ‘popped-up’ in individuals who have unaffected parents. This tells us that the condition must be recessive, that the affected individuals must be homozygous recessive (aa) and that their unaffected parent must be carriers (Aa) –that is they are "carriers" of the disease-causing allele but are unaffected because they also carry the dominant, normal allele. If affected individuals have two unaffected parents, the condition must be recessive. ==Dominant Condition== [image:http://i.imgur.com/9kzt9ZX.png] Every affected individual shown has an affected parent suggesting that this is most likely a dominant characteristic. If the disorder were recessive, we might expect to see some affected individuals with unaffected parents. Thus, all the affected individuals probably carry a dominant allele (they are AA or Aa) while all the unaffected individuals must be homozygous recessive (aa). However, this isn't actually conclusive evidence. The only definitive evidence that a condition is dominant is if two affected individuals have an unaffected child (basically proof that 'unaffected' is recessive) =Tips for answering questions= [image:http://i.imgur.com/mfvlb1x.png] This pedigree was taken from a previous exam question. Shaded Individuals have a genetic disorder. Students were asked to identify the genotype of individual C. ===Step One: Dominant or Recessive?=== This condition is most likely dominant as every affected individual also has an affected parent. Conclusive proof comes from the fact that two affected individuals (B and C) have an unaffected child. '''Always keep a look out for a child who is different from both their parents''' -this indicates that the child has the recessive trait and that the parent's trait is dominant. ===Step Two: Label everyone A_ or aa=== Because the condition is dominant any affected individuals must carry at least one dominant allele so we can label them A_ for now. Any unaffected individuals must be aa. [image:http://i.imgur.com/x9b5oQw.png?2] ===Step Three: Fill in the gaps=== By looking at the parents or children of a given individual, we can often fill in any gaps in their genotype. For instance we know individual C must be A_ because they have the disorder which is dominant. However individual C has an unaffected mother (aa), so she must have inherited one of these recessive alleles from her mother also. Thus individual C must be Aa. We could have also determined this by looking at her children. One of her children is unaffected (aa), so must have inherited one of these recessive allele from her mother. Individual C • Phenotype: Has the genetic disorder (affected) • Genotype: Aa