Section 12.1 Summary – pages 309 - 314

1. Section 12.1 Summary – pages 309 - 314 Pedigrees illustrate inheritance • Pedigree - 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.

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

3. Section 12.1 Summary – pages 309 - 314 Pedigrees illustrate inheritance Female Male I 1 2 II 2 1 4 5 3 • Circle = female • Square = male. III 1 4 2 3 ? IV 5 3 4 2 1

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

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

6. Section 12.1 Summary – pages 309 - 314 Pedigrees illustrate inheritance • Half-shaded circle or square is a carrier, a heterozygous individual.

7. Section 12.1 Summary – pages 309 - 314 Pedigrees illustrate inheritance • A horizontal line connecting a circle and a square indicates that the individuals are parents, and a vertical line connects parents with their offspring. I 1 2 II 4 2 3 1 5 III 1 4 2 3 ? IV 2 3 5 1 4

8. Section 12.1 Summary – pages 309 - 314 Pedigrees illustrate inheritance • Each horizontal row of circles and squares in a pedigree designates a generation, with the most recent generation shown at the bottom. I 1 2 II 3 1 2 4 5 III 1 2 4 3 ? IV 3 5 1 2 4

9. Section 12.1 Summary – pages 309 - 314 Pedigrees illustrate inheritance • The generations are identified in sequence by Roman numerals, and each individual is given an Arabic number. I 1 2 II 3 1 2 4 5 III 1 2 4 3 ? IV 3 5 1 2 4

10. Section 12.1 Summary – pages 309 - 314 Simple Dominant and Recessive Genetic Disorders • Recessives: • Cystic fibrosis • Tay-Sachs • Phenylketonuria (PKU) • Dominant: • Huntington’s

11. Section 12.1 Summary – pages 309 - 314 Cystic fibrosis • Cystic fibrosis (CF) is common among white Americans. • Caused by a defective transport protein in plasma membranes. • Results in the formation and accumulation of thick mucus in the lungs and digestive tract.

12. Section 12.1 Summary – pages 309 - 314 Tay-Sachs disease • Tay-Sachsdisease is a lethal disorder of the central nervous system. • Results in the absence of an enzyme that normally breaks down a lipid produced and stored in tissues of the central nervous system. • Because this lipid fails to break down properly, it accumulates in nerve cells and causes severe neurologic damage.

13. Section 12.1 Summary – pages 309 - 314 I 1 2 Typical Pedigree for II 1 2 4 3 Tay-Sachs III 3 1 2 IV 1

14. Section 12.1 Summary – pages 309 - 314 Phenylketonuria • Phenylketonuria (PKU) is results from the absence of an enzyme that converts phenylalanine to tyrosine. • Causes severe damage to the central nervous system. • Infants affected by PKU are given a diet that is low in phenylalanine until their brains are fully developed.

15. 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.

16. 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. • How has the allele for Huntington’s been able to persist within the human population? • Onset of Huntington’s is usually between 30 and 50, after the individual may already have had children.

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

18. Section 1 Check Question 1 I 1 2 What does this pedigree tell you about those who show the recessive phenotype for the disease? II 1 2 4 3 III 3 1 2 IV 1 NC: 3.03