Human Inheritance

1. Human Inheritance

2. Impacts, Issues:Strange Genes, Tortured Minds • Exceptional creativity often accompanies neurobiological disorders such as schizophrenia, autism, chronic depression, and bipolar disorder • Examples: Lincoln, Woolf, and Picasso

3. 12.1 Human Chromosomes • Males have XY sex chrom, females have XX • All other chromosomes are autosomes– chromosomes that are same in males and females

4. Sex Determination in Humans • Sex of a child is determined by the father • Eggs have an X chromosome; sperm have X or Y

5. Autosomal Dominant Inheritance • A dominant autosomal allele is expressed in homozygotes and heterozygotes • Tends to appear in every generation • With one homozygous recessive and one heterozygous parent, children have a 50% chance of inheriting and displaying the trait • Examples: achondroplasia, Huntington’s disease

6. Autosomal Recessive Inheritance • Autosomal recessive alleles are expressed only in homozygotes; heterozygotes are carriers and do not have the trait • A child of two carriers has a 25% chance of expressing the trait • Example: galactosemia

7. Autosomal Inheritance

8. Fig. 12-4a, p. 188

9. Fig. 12-4b, p. 188

10. Galactosemia

11. Neurobiological Disorders • Most neurobiological disorders do not follow simple patterns of Mendelian inheritance • Depression, schizophrenia, bipolar disorders • Multiple genes and environmental factors contribute to NBDs

12. 12.3 Too Young to be Old • Progeria • Genetic disorder that results in accelerated aging • Caused by spontaneous mutations in autosomes

13. 12.4 Examples of X-Linked Inheritance • X chromalleles give rise to phenotypes that reflect Mendelian patterns of inheritance • Mutated alleles on the X chromosome cause or contribute to over 300 genetic disorders

14. X-Linked Inheritance Patterns • More males than females have X-linked recessive genetic disorders • Males have only one X chromosome and can express a single recessive allele • A female heterozygote has two X chromosomes and may not show symptoms • Males transmit an X only to their daughters, not to their sons

15. X-Linked Recessive Inheritance Patterns

16. Some X-Linked Recessive Disorders • Hemophilia A • Bleeding caused by lack of blood-clotting protein • Red-green color blindness • Inability to distinguish certain colors caused by altered photoreceptors in the eyes • Duchenne muscular dystrophy • Degeneration of muscles caused by lack of the structural protein dystrophin

17. Hemophilia A in Descendents of Queen Victoria of England

18. Nondisjunction • Changes in chronumber cause nondisjunction, when a pair of chromfails to separate during meiosis • Affects the chromosome number at fertilization • Monosomy (n-1 gamete) • Trisomy (n+1 gamete)

19. Nondisjunction

20. Autosomal Change and Down Syndrome • Only trisomy 21 (Down syndrome) allows survival to adulthood • Characteristics include physical appearance, mental impairment, and heart defects • Incidence of nondisjunction increases with maternal age • Can be detected through prenatal diagnosis

21. Trisomy 21

22. Down Syndrome and Maternal Age

23. Change in Sex Chromosome Number • Changes in sex chromnumber may impair learning or motor skills • Female sex chromabnormalities • Turner syndrome (XO) • XXX syndrome (three or more X chromosomes) • Male sex chromosome abnormalities • Klinefelter syndrome (XXY) • XYY syndrome

24. Turner Syndrome • XO (one unpaired X chromosome) • Usually caused by nondisjunction in the father • Results in females with undeveloped ovaries

25. 12.7 Human Genetic Analysis • Charting genetic connections with pedigrees reveals inheritance patterns for certain alleles • Pedigree • A standardized chart of genetic connections • Used to determine the probability that future offspring will be affected by a genetic abnormality or disorder

26. Defining Genetic Disorders and Abnormalities • Genetic abnormality • A rare or uncommon version of a trait; not inherently life threatening • Genetic disorder • An inherited condition that causes mild to severe medical problems, characterized by a specific set of symptoms (a syndrome)

27. Some Human Genetic Disorders and Genetic Abnormalities

28. Constructing a Pedigree for Polydactyly

29. 12.8 Prospects in Human Genetics • Genetic analysis can provide parents with information about their future children • Genetic counseling • Starts with parental genotypes, pedigrees, and genetic testing for known disorders • Information is used to predict the probability of having a child with a genetic disorder

30. Prenatal Diagnosis • Tests done on an embryo or fetus before birth to screen for sex or genetic problems • Involves risks to mother and fetus • Three types of prenatal diagnosis • Amniocentesis • Chorionic villus sampling (CVS) • Fetoscopy

31. Amniocentesis

32. Fetoscopy

33. Preimplantation Diagnosis • Used in in-vitro fertilization • An undifferentiated cell is removed from the early embryo and examined before implantation

34. After Preimplantation Diagnosis • When a severe problem is diagnosed, some parents choose an induced abortion • In some cases, surgery, prescription drugs, hormone replacement therapy, or dietary controls can minimize or eliminate symptoms of a genetic disorder • Example: PKU can be managed with dietary restrictions

35. Genetic Screening • Genetic screening (widespread, routine testing for alleles associated with genetic disorders) • Provides information on reproductive risks • Identifies family members with a genetic disorder • Used to screen newborns for certain disorders • Used to estimate the prevalence of harmful alleles in a population