Pedigree Analysis, Applications, and Genetic Testing Benjamin A. Pierce GENETICS A Conceptual Approach FIFTH EDITION CHAPTER 6 Pedigree Analysis, Applications, and Genetic Testing © 2014 W. H. Freeman and Company

The Mystery of Missing Fingerprints

6.1 The Study of Genetics in Humans Is Constrained by Special Features of Human Biology and Culture Controlled mating is not possible Long generation time Small family size

6.2 Geneticists Often Use Pedigrees to Study the Inheritance of Characteristics in Humans Pedigree: pictorial representation of a family history, a family tree that outlines the inheritance of one or more characteristics. Proband: the person from whom the pedigree is initiated.

Figure 6.2 Standard symbols are used in pedigrees.

6.2 Geneticists Often Use Pedigrees to Study the Inheritance of Characteristics in Humans Autosomal recessive traits: Fig. 6.4 Autosomal dominant traits: Fig. 6.5 X-linked recessive traits: Fig. 6.7 & 6.8 X-linked dominant traits: Fig. 6.9 Y-inked traits: Fig. 6.10

Figure 6.4 Autosomal recessive traits normally appear with equal frequency in both sexes and seem to skip generations.

Figure 6.5 Autosomal dominant traits normally appear with equal frequency in both sexes and do not skip generations.

Figure 6.7 X-linked recessive traits appear more often in males than in females and are not passed from father to son.

Figure 6.8 Classic hemophilia is inherited as an X-linked recessive trait. This pedigree is of hemophilia in the royal families of Europe.

Figure 6. 9 X-linked dominant traits affect both males and females Figure 6.9 X-linked dominant traits affect both males and females. An affected male must have an affected mother.

Figure 6.10 Y-linked traits appear only in males and are passed from a father to all his sons.

Concept Check 1 Autosomal recessive traits often appear in pedigrees in which there have been consanguine mating, because these traits: a. tend to skip generations. b. appear only when both parents carry a copy of the gene for the trait, which is more likely when the parents are related. c. usually arise in children born to parents who are unaffected. d. appear equally in males and females.

Concept Check 1 Autosomal recessive traits often appear in pedigrees in which there have been consanguine mating, because these traits: a. tend to skip generations. b. appear only when both parents carry a copy of the gene for the trait, which is more likely when the parents are related. c. usually arise in children born to parents who are unaffected. d. appear equally in males and females.

Concept Check 2 How could you distinguish between an autosomal recessive trait with higher penetrance in males and an X-linked recessive trait?

Concept Check 2 How could you distinguish between an autosomal recessive trait with higher penetrance in males and an X-linked recessive trait? X-linked recessive traits are only passed to sons from mothers, not from fathers.

Dizygotic twins = nonidentical twins 6.3 Studying Twins and Adoptions Can Help Assess the Importance of Genes and Environment Dizygotic twins = nonidentical twins Monozygotic twins = identical twins Concordant trait: The trait shared by both members of a twin pair. Concordance: The percentage of twin pairs that are concordant for a trait. Table 6.2 Twin studies and obesity: Table 6.3

Fig. 6.12 Twin studies have shown that asthma is caused by a combination of genetic and environmental factors.

Concept Check 3 A trait exhibits 100% concordance in both monozygotic and dizygotic twins. What conclusion can you draw about the role of genetic factors in determining differences in the trait? a. Genetic factors are extremely important. b. Genetic factors are somewhat important. c. Genetic factors are unimportant. d. Both genetic and environment factors are important.

Concept Check 3 A trait exhibits 100% concordance in both monozygotic and dizygotic twins. What conclusion can you draw about the role of genetic factors in determining differences in the trait? a. Genetic factors are extremely important. b. Genetic factors are somewhat important. c. Genetic factors are unimportant. d. Both genetic and environment factors are important.

Figure 6.13 Adoption studies demonstrate that obesity has a genetic influence. [Redrawn with the permission of the New England Journal of Medicine 314:195, 1986.]

6.4 Genetic Counseling and Genetic Testing Provide Information to Those Concerned About Genetic Diseases and Traits Genetic counseling: provides information related to hereditary conditions.

Genetic conditions recommended for mandatory screening by the American College of Medical Genetics.

Figure 6.15 Amniocentesis is a procedure for obtaining fetal cells for genetic testing.

Figure 6.16 Chorionic villus sampling (CVS) is another procedure for obtaining fetal cells for genetic testing.

Interpreting Genetic Testing More than a thousand genetic tests available Complicated by several factors: Some diseases caused by numerous mutations Incomplete penetrance and environmental factors

Genetic Discrimination and Privacy Many new genetics tests 1970s: African Americans carrying sickle-cell trait had difficulty finding employment and health insurance Genetic Information Nondiscrimination Act