Chapter 25 Heredity and Hereditary Diseases

1. Chapter 25 Heredity andHereditary Diseases

2. Key Terms allele genetic pedigree chart amniocentesis genotype phenotype autosome heredity progeny carrier heterozygous recessive chromosome homozygous sex-linked congenital karyotype teratogen dominant meiosis trait familial mutagen gene mutation

3. Genes and Chromosomes Genes • Segments of DNA contained in the chromosomes • Control manufacture of protein synthesis • An allele is a specific version of a given gene Chromosomes • During mitosis, the DNA that makes up the chromosomes is replicated and distributed to daughter cells • 46 chromosomes in humans • 22 autosome pairs • One sex chromosome pair

4. Genes and Chromosomes (cont.) Figure 25-1 Genes and chromosomes.

5. Genes and Chromosomes (cont.) Dominant and Recessive Alleles • Gene pairs • Homozygous—both genes are same • Heterozygous—the two genes differ • Dominant allele • Express effect whether homozygous or heterozygous • Need to inherit from one parent only • Recessive allele • Only expressed if homozygous • Need to inherit from both parents

6. Genes and Chromosomes (cont.) Dominant and Recessive Alleles (cont.) • Phenotype: Any characteristic that can be observed or tested for • Example: Eye color, blood type • Genotype: A person’s genetic makeup • Example: Heterozygous dominant Bb (a carrier) Homozygous dominant BB Homozygous recessive bb

7. Genes and Chromosomes (cont.) Distribution of Chromosomes to Offspring • Reproductive cells produced by meiosis • Two meiotic divisions • First meiotic division distributes the chromosome pair into separate cells • Second meiotic division separates the strands of the duplicated chromosome and distributes to an individual gamete

8. Figure 25-2 Meiosis. Genes and Chromosomes (cont.) How many cells are produced in one complete meiosis?

9. Genes and Chromosomes (cont.) Punnett Squares A grid showing all the combinations of alleles that can result from a given parental cross • Capital letter represents the dominant allele • Lower-case letter represents the recessive allele What percentage of children from this cross will show the recessive phenotype? What percentage will be heterozygous?

10. Genes and Chromosomes (cont.) Sex Determination • Sex chromosomes not matched in size or appearance • Female (X) chromosome larger • Male (Y) chromosome smaller • Sex • Females: Two X chromosomes—XX • Males: An X and a Y chromosome—XY

11. Figure 25-4 Sex determination. Genes and Chromosomes (cont.) What percentage of children from this cross will show the recessive phenotype? What percentage will be heterozygous?

12. Genes and Chromosomes (cont.) Sex-Linked Traits • Traits carried on sex chromosomes (mostly X chromosome) • Most are recessive • Usually males exhibit trait • Heterozygous females are carriers inherited from mother

13. Figure 25-5 Inheritance of sex-linked traits. Genes and Chromosomes (cont.) What is the genotype of a carrier female?

14. Hereditary Traits (cont.) • Observable hereditary traits are skin, eye, and hair color • Less clearly defined traits are weight, body build, life span, and susceptibility to disease • Single-gene inheritance; less common • Multifactorial (multiple gene) inheritance; most common • Produces wide range of variation

15. Hereditary Traits (cont.) Gene Expression • Influenced by: • Sex • Other genes • Codominance • Incomplete dominance • The environment

16. Hereditary Traits (cont.) Genetic Mutation A change in a gene or chromosome • May be caused by: • Chromosomal breakage or loss • Gene fragment rearrangement • May occur during cell division • Spontaneous • Induced by a mutagen

17. Figure 25-6 Genetic exchange. Hereditary Traits (cont.)

18. Hereditary Traits (cont.) Mitochondrial Inheritance • Mitochondria contain some DNA • Multiplies independently • Can mutate, resulting in disease • Passed only from the mother to offspring

19. Genetic Diseases (cont.) Congenital versus Hereditary Diseases • Congenital means present at the time of birth • Hereditary means genetically transmitted • May not manifest until later in life Causes of Congenital Disorders • Often not known • Certain infections and toxins transmitted from mother (e.g., German measles) • Teratogen (agent, i.e., drug) • Ionizing radiation

20. Genetic Diseases (cont.) Causes of Congenital Disorders (cont.) • Alcohol intake • Fetal alcohol syndrome (FAS) • Cigarette smoking • Poor nutrition • Spina bifida related to inadequate folic acid

21. Figure 25-7 Congenital and hereditary diseases. Genetic Diseases (cont.)

22. Figure 25-8 Fetal alcohol syndrome. Genetic Diseases (cont.)

23. Figure 25-9 Spina bifida. Genetic Diseases (cont.)

24. Genetic Diseases (cont.) Chromosomal Disorders • Down syndrome (trisomy 21) • Klinefelter syndrome • Turner syndrome • Dominant gene disorders • Huntington disease • Marfan syndrome

25. Genetic Diseases (cont.) Chromosomal Disorders (cont.) • Recessive gene disorders • Phenylketonuria (PKU) • Sickle cell anemia • Cystic fibrosis • Tay-Sachs disease • Progressive muscular atrophies • Albinism • Fragile X syndrome • Osteogenesis imperfecta • Neurofibromatosis

26. Figure 25-10 Chromosomal disorders. Genetic Diseases (cont.)

27. Treatment and Prevention of Genetic Diseases (cont.) • More than 4,000 genetic diseases identified • List is growing as science advances Genetic Counseling • Team approach • Those who might consider genetic counseling: • Prospective parents over 35 years of age • Family history of genetic disorders • Considering some form of fertility treatment

28. Treatment and Prevention of Genetic Diseases (cont.) Genetic Counseling (cont.) • Family history • Pedigree chart • Laboratory studies • First-trimester prenatal screening: • Nuchal transparency test • Pregnancy-associated plasma protein test • Human chorionic gonadotropin test

29. Treatment and Prevention of Genetic Diseases (cont.) • Laboratory studies (cont.) • Second-trimester screening • Alpha-fetoprotein (AFP) screening • Estriol test • Inhibin test • Amniocentesis • Chorionic villus sampling • Karyotyping

30. Figure 25-11 A pedigree (family history) showing three generations (F1–F3). Treatment and Prevention of Genetic Diseases (cont.) What are the possible genotypes of the two normal children in the F3 generation?

31. Figure 25-12 Prenatal testing. Treatment and Prevention of Genetic Diseases (cont.)

32. Figure 25-13 Karyotype. Treatment and Prevention of Genetic Diseases (cont.) Look closely at this karyotype. How many chromosomes are present? What is the gender of the baby, and what genetic disorder is represented?

33. Treatment and Prevention of Genetic Diseases (cont.) Counseling Prospective Parents • Counselors have pertinent facts from family history and laboratory studies • Prospective parents may use information to make decisions

34. Treatment and Prevention of Genetic Diseases (cont.) Progress in Medical Treatment • Dietary control for certain diseases • Examples • Maple syrup urine disease • Wilson disease • Phenylketonuria • Vitamins • Hormones • Future: Possible treatment or correction of genetic disorder with genetic engineering

35. Case Study Role of a Genetic Counselor • Works as part of a team along with physicians, nurses, laboratory, and social service professionals • Collects all of the pertinent facts from the family history and laboratory studies • Has knowledge of genetic inheritance patterns • Presents information and discuss with prospective parents/parents the inheritance of their children

36. Word Anatomy (cont.)

37. Word Anatomy (cont.)