1. Patterns of Heredity Pedigrees March 19, 2010

2. 12.1 Section Objectives – page 309 Interpret a pedigree. Section Objectives: Identify human genetic disorders caused by inherited recessive alleles. Predict how a human trait can be determined by a simple dominant allele.

3. Section 12.1 Summary – pages 309 - 314 A pedigree is a graphic representation of genetic inheritance. It is a diagram made up of a set of symbols that identify males and females, individuals affected by the trait being studied, and family relationships. It is like a family tree for your genes. Pedigrees illustrate inheritance

4. Section 12.1 Summary – pages 309 - 314 Key for Understanding Pedigrees Male Female Affected male Affected female Mating Parents Siblings Known heterozygotes for recessive allele Death

5. Section 12.1 Summary – pages 309 - 314 In a pedigree, a circle represents a female; a square represents a male. Pedigrees illustrate inheritance Female Male ? I II III IV 1 2 1 1 1 3 2 2 2 4 3 3 5 4 4 5

6. Section 12.1 Summary – pages 309 - 314 Highlighted circles and squares represent individuals showing the trait being studied. ? I II III IV 1 2 1 1 1 3 2 2 2 4 3 3 5 4 4 5 Pedigrees illustrate inheritance

7. Section 12.1 Summary – pages 309 - 314 Pedigrees illustrate inheritance Circles and squares that are not highlighted designate individuals that do not show the trait. ? I II III IV 1 2 1 1 1 3 2 2 2 4 3 3 5 4 4 5

8. Section 12.1 Summary – pages 309 - 314 A half-shaded circle or square represents a carrier, a heterozygous individual. Pedigrees illustrate inheritance

9. Section 12.1 Summary – pages 309 - 314 Simple Recessive Heredity Most genetic disorders are caused by recessive alleles. Cystic fibrosis Cystic fibrosis (CF) is a fairly common genetic disorder among white Americans. Another is Tay-Sachs (tay saks) disease. It is a recessive disorder of the central nervous system.

10. Section 12.1 Summary – pages 309 - 314 I II III IV Typical Pedigree for 1 2 1 1 1 3 2 2 4 3 Tay-Sachs Who had this disease? Tay-Sachs Who had this disease?

11. Section 12.1 Summary – pages 309 - 314 Huntington’s disease Huntington’s disease is a lethal genetic disorder caused by a rare dominant allele. It results in a breakdown of certain areas of the brain.

12. Section 12.1 Summary – pages 309 - 314 Huntington’s disease Ordinarily, a dominant allele with such severe effects would result in death before the affected individual could have children and pass the allele on to the next generation. But because the onset of Huntington’s disease usually occurs between the ages of 30 and 50, an individual may already have had children before knowing whether he or she is affected.

13. Section 12.1 Summary – pages 309 - 314 Typical Pedigree of Huntington’s Disease I 1 II III 2 1 1 3 2 2 4 3 45 5