1. PEDIGREE CHARTS (and Test Crosses) Biology 12

2. Review: Each Pair of Gene Alleles Is Separated and Two Alleles End Up in Different Gametes

3. A Testcross Can Reveal Genotypes: Used if one is unsure if there is a homozygous dominant or heterozygous individual o In order to determine the genotype of these individuals a test cross must be performed Cross unknown (TT or Tt) with a homozygous recessive (tt) o If any offspring show the recessive trait then the unknown must be heterozygous. o If all offspring show the dominant trait the unknown must be homozygous.

4. Example Test Cross: Tt tt TT x tt tttt t T T T Tt x tt Offspring: all dominant phenotypeOffspring:1/2 dominant, ½ recessive

5. What is a pedigree chart? Pedigree charts show a record of the family of an individual They can be used to study the transmission of a hereditary condition They are particularly useful when there are large families and a good family record over several generations.

6. Goals of Pedigree Analysis 1. Determine the mode of inheritance: dominant, recessive, partial dominance, sex-linked, autosomal, mitochondrial, maternal effect. 2. Determine the probability of an affected offspring for a given cross.

7. What symbols are used?

8. o Example: family with 5 children. The pedigree chart shows that the second son is affected by the condition.

9. Organising the pedigree chart: o Children are list oldest to youngest from left to right o Generations are identified by Roman numerals I II III IV

10. o Individuals in each generation are identified by both a.Roman numerals (indicated generation) b.Numbered from the left Example: The affected individuals below are II-3, IV-2 and IV-3

11. Dizygotic twins Adopted Monozygotic twins Consanguineo us marriage Sex unspecified Divorced Number of children of each sex indicated Multiple marriage AffectedExtra marital union Some other symbols:

12. Example: A pedigree chart of a family showing 20 individuals

13. To do: o Go back and add a pedigree chart to #7 on the Monohybrid Cross Assignment o Pedigree Studies Activity o Page 142 #1,2 o Page 148 # 3 (Dominant allele for PKU, so if a person has one “big letter” they show symptoms of the disease)