Genetics

1. Genetics U.K. College of Nursing

2. Genes and Chromosomes • Each cell contains 23 pairs of matched chromosomes for a total of 46 chromosomes per cell. • One chromosome from each pair is inherited from each parent. • There are 22 pairs of autosomes, which control most traits in the body, and one pair of sex chromosomes, which determine gender and other traits.

3. Genes and Chromosomes • Some genes are dominant and their characteristics are expressed even if only on one chromosome. • Some genes are recessive and their characteristics will be expressed only if they are carried by both chromosomes in a pair.

4. Group Exercise Human Variation

5. Punnet Squares • Visual representation of the principles of inheritance • Dominant trait--Capital letter • Recessive trait--Small letter • Male vs female trait/gene

8. Patterns of Inheritance • Autosomal Dominant • Autosomal Recessive • Sex-Linked (or X-linked) Dominant • Sex-Linked (or X-linked) Recessive • Chromosomal Abnormalities • Congenital Anomalies

9. Autosomal Dominant • Trait appears in every generation (does not skip) • Both males and females are affected • Each pregnancy of an affected person has a 50% chance of producing an affected offspring

10. Autosomal Dominant Disorders • Disorders • Huntington’s Disease • Retinitis Pigmentosa • Polycystic Kidney Disease • Achodroplasia • Marfan Syndrome

11. Autosomal Dominant Disorders- Marfan Syndrome

12. Autosomal Dominant Inheritance

13. Autosomal Dominant • Clinical Situation-- • One parent is unaffected • One parent carries the defective gene for Marfan Syndrome • Draw the Punnet Square

14. Autosomal Dominant Punnett Square

15. Autosomal Recessive • Both parents are usually unaffected, but are carriers • Trait first appears only in siblings rather than in parents • Trait found equally in males and females • 25% risk when both parents are carriers • Increased incidence with consanguinity

16. Autosomal Recessive • Disorders • Phenylketonuria • Fanconi’s Anemia • Tay Sachs Disease • Sickle Cell Anemia • Cystic Fibrosis

17. Autosomal Recessive Inheritance

18. Autosomal Recessive • Clinical Situation • Male carries the defective gene for Tay Sachs disease • Female carries the defective gene for Tay Sachs disease • Draw the Punnett Square

19. Autosomal Recessive Punnett Square

20. X-linked Inheritance • Sex-Modified Traits - Dominant genes are expressed in both males & females but at differing frequencies • Ex: Baldness - expressed as dominant in males, but recessive in females, never as severe in females

21. X-linked Dominant • Very rare • Often lethal in males therefore few males present in the pedigree • Multiple miscarriages may be present • No carrier status, all individuals with the gene are affected • Trait appears in every generation

22. X-linked Dominant • Female children of affected males will all be affected (100% risk); no male to male transmission. • Homozygous females (both X chromosomes are affected) have a 100% chance of having an affected child of either sex. • Heterozygous females (only one X affected) have a 50% of having an affected child witheach pregnancy.

23. X-linked Dominant Disorders • Hypophosphatemic Rickets • Fragile X Syndrome

24. Fragile X Syndrome

25. X-linked Dominant • Clinical Situation • Male is affected with hypophosphatemic rickets • Female is unaffected • Draw the Punnet square

26. X-linked Dominant Punnet Square

27. X-linked Recessive • Incidence of trait much higher among males in a kinship than among females • Trait cannot be transmitted from father to son • An affected male will pass the carrier status to all his daughters • Female carriers have a 50% risk of transmitting the gene to their offspring witheach pregnancy

28. X-linked Recessive • Disorders • Hemophilia A • Duchenne’s Muscular Dystrophy • Color-Blindness

29. Duscenne’s Muscular Dystrophy

30. X-Linked Recessive Inheritance

31. X-linked Recessive • Clinical Situation • Male is affected with Hemophilia A • Female is normal (non-carrier) • Draw the Punnett Square • Use X1 for chomosome with normal allele and X2 for chromosome with disease allele

32. X-linked Recessive Punnet Square

33. X-linked Recessive • Clinical Situation • Male is normal • Female is a carrier of color-blindness • Draw the Punnett Square

34. X-linked Recessive Punnett Square

35. X-linked Recessive • Clinical Situation • Male is affected with Duschenne Muscular Dystrophy • Female is carrier of Duschenne Muscular Dystrophy • Draw the Punnett Square

36. X-linked Recessive Punnett Square

37. Genotype - The actual gene constitution of a given person. • Phenotype - The observable characteristics of a given person

38. Traits can be environmentally modified • type 2 diabetes • PKU • Traits can be medically modified • Sickle cell disease (bone marrow transplant) • Polycysitc kidney disease (kidney transplant) • However, genotype stays the same so next generation are not saved from condition

39. Group Exercise Punnet Squares and Patterns of Inheritance

40. Karyotypes • The arranged representation of the chromosomal make-up of a cell nucleus

44. Chromosomal Abnormalities • Abnormalities in number of chromosomes • Caused by nondisjunction: failure of homologous chromosomes or sister chromatids to separate properly into different progeny cells • Monosomy - condition in which one chromosome of a pair is missing from a somatic cell

45. Monosomy X - Turners Syndrome

46. Monosomy--Turner’s Syndrome

47. Chromosomal Abnormalities • Trisomy - condition in which one chromosome in the pair is pesent in three copies in a somatic cell • Down Syndrome (21), Trisomy 13 or 18 • Klinefelter’s Syndrome - XXY

48. Abnormalities of Chromosome Number Trisomy

50. Chromosomal Structural Abnormalities • Deletions - absence of normal chromosomal material; can be terminal or interstitial • Duplications - presence of an extra copy of a chromosomal segment • Inversions - Intrachromosomal re-arrangement such that the rearranged section is inverted • Ring Chromosome - Fusion of the ends of a chromosome that forms a circle or ring