Standard Biology Chapter 27 Human Genetics

1. Standard BiologyChapter 27 Human Genetics 27.1 The Role of Chromosomes Very complicated compared to peas!

2. Chromosome Number • Each human sperm and egg has 23 different chromosomes • Each human body cell has 46 chromosomes (23 pair) • Different organisms have different number of chromosomes- most are paired (Homologous) • Table 27-1 Chromosome Number p. 566 (next slide)

3. Chromosome Number

4. A Way to Tell Chromosome Number • Amniocentesis: a look at chromosomes in fetus • Performed 15-20 weeks gestation • Needle inserted into mother’s abdomen into amniotic fluid surrounding the fetus. Some fluid removed which also contains cells from the fetus. • Cells grown for 10 days, watch for dividing cells.

5. A Way to Tell Chromosome Number • Amniocentesis, cont. • Study the dividing cells (easy to see chromosomes as sister chromatids) • Arrange chromosomes in a karyotype

6. Karyotype Chromosome smear Karyotype

7. Karyotype • Ordered arrangement of chromosome pairs by number • Largest is #1, smallest is #22 • Match up banding pattern on chromosomes • Can determine sex of fetus by sex chromosomes • XY is male • XX is female • Y chromosome is much smaller than X

8. A Way to Tell Chromosome Number • Chorionic villi sampling (same idea as amniocentesis) • Use a piece of the placenta • Can do earlier in pregnancy and get results sooner • May not be as accurate

9. Sex- A Genetic Trait • Chromosomes # 1-22 are autosomes • Don’t determine sex • Are the same in males and females • Called non sex or body chromosomes • Males are XY so make X sperm and make Y sperm • Females are XX so only make X eggs

10. Sex- A Genetic Trait

11. Sex- A Genetic Trait • Males determine the sex of the child

12. Standard BiologyChapter 27 Human Genetics 27.2 Human Traits

13. Humans have many traits: those you can see and those you can’t.

14. Survey of Human Traits • Dominant traits • Freckles • Dimples

15. Survey of Human Traits • Recessive traits • Attached ear lobes • Straight hair • Nonroller tongue • Short eyelashes

16. Survey of Human Traits • L=long eyelash trait • l=short eyelash trait • Both parents are heterozygous and have long eyelashes • Expect 3:1 long to short eyelashes in offspring or expressed as a %, expect 75% long eyelashes children and 25% short eyelashes children

17. Survey of Human Traits L l L=long eyelash trait l=short eyelash trait Both parents are heterozygous and have long eyelashes L LL Ll l ll Ll

18. Incomplete Dominance • One trait not completely dominant over the other • Heterozygotes show in between trait • Example: Snapdragon flower color R=red, r=white; Parents are pink (heterozygous)

19. Incomplete Dominance

20. Incomplete Dominance • Example: Sickle cell Anemia p. 574 • RR=round red blood cells • R’R’= sickle red blood cells

21. Incomplete Dominance • Sickle cell Anemia • Serious health problems because sickle cells cannot carry enough oxygen • Causes pain and fatigue (tiredness) because sickle cell block capillaries • Sickle cell Anemia most in African Americans

22. Incomplete Dominance • Sickle cell Anemia • RR’= both round and sickle red blood cells • Usually no health problems because enough health red blood cells to carry oxygen

23. Blood Types in Humans

24. Blood Types in Humans • Three genes: A, B, and O • A and B are dominant to O • A and B are codominant

25. Genes on the X Chromosome • Sex chromosomes carry genes • X chromosome has many genes because it is a large chromosome • Y chromosome has few genes because it is a small chromosome • X chromosome and Y chromosome do have the same genes

26. Genes on the X Chromosome • Females are XX have 2 copies of each gene • Males are XY have 1 copy of X genes and 1 copy of Y genes

27. Color Blindness

28. Color Blindness • Color blindness gene on X chromosome p. 576 • Red and green shades look alike • Females 2 copies of color blindness gene; color blind if both copies are recessive (cc)/ not color blind if heterozygous (Cc) or if homozygous dominant (CC)

29. Color Blindness • Males 1 copy of color blindness gene; color blind if the one is recessive (c)/ not color blind if the one gene is dominant (C) • Males are more likely to be color blind • Females are carriers when they are heterozygous (Cc) • Example: Normal male (XCY), female carrier (XCXc)

30. Color Blindness XC XC Example: Normal male (XCY) female carrier (XCXc) XC XCXC XCXc Y XCY XcY

31. Color Blindness XC Xc Example: Color blind male (XcY), female carrier (XCXc) 50% color blind females 50% color blind males Xc XCXc XcXc Y XCY XcY

32. Color Blindness • This is called a sex-linked genes because it is located on the X chromosome • Another sex linked gene is hemophilia (blood clotting disorder)

33. Standard BiologyChapter 27 Human Genetics 27.3 Genetic Disorders About 600 babies born each day in the U.S. with a disorder, some are genetic disorders.

34. Errors in Chromosome Number • Can happen if baby has more than 46 chromosomes • Can happen if baby has less than 46 chromosomes • Can happen if sperm or egg have more or less than 23 chromosomes

35. Errors in Chromosome Number • Error happens during meiosis when sister chromatids don’t separate correctly; get one sex cell with 22 the other with 24 chromosomes • Can happen to any of your chromosomes

36. Down Syndrome (Trisomy 21) • 3 copies of chromosome #21

37. Down Syndrome (Trisomy 21) • mental retardation, heart problems, facial abnormalities

38. Down Syndrome (Trisomy 21) • 1 in 700 births • Increasing incidence with increasing age of mother

39. Turner’s Syndrome • Female with only 1 X chromosome (X0) • No neck, short, mental retardation, do not develop secondary sex characteristics • 1 in 5000 births

40. Genetic Disorders and Sex Chromosomes • Hemophilia • Failure of blood to clot • Bruising • Significant in royal families of Europe (Russia)

41. Genetic Disorders and Sex Chromosomes • Color blindness • Cannot distinguish red/green shades

42. Genetic Disorders and Autosomes • Dyslexia (dominant gene) • “Word blindness” • See and/or write letters and words backwards, difficult to learn to read

43. Genetic Disorders and Autosomes • PKU- phenylketonuria • Amino acid phenylalanine can’t breakdown in body, builds up causing mental retardation • Now tested at birth and babies are given special diet with low levels of this amino acid

44. Genetic Counseling • Looks at family history to determine genetic disorder • Use of genetics to predict and explain traits in children • Genetic counselor- person trained to interpret medical information and counsel patients

45. Genetic Counseling • Answer questions: • How did the baby get this disorder? • If the baby is healthy, does it have a problem gene? • Is the trait dominant or recessive? • What will happen to baby’s health as it gets older? • What are the chances that future children will have the trait? • What medical treatment is available?

46. Genetic Counseling • Genetic counselors use a pedigree (diagram of family history) that can show how a certain trait is passed along in a family

47. Cystic Fibrosis • Recessive genetic disorder • Symptoms of disease: excess and thick mucus, respiratory problems and digestive problems • Child with the disease 1 in 4 chance if parents are heterozygous F f F FF Ff f Ff ff

48. Cystic Fibrosis Pedigree 1 2 I II 1 2 3 4 5 1 2 3 4 III 1 2 3 4 IV 5

49. Pedigree Analysis • Are females • Are males • Shaded in circles and squares are affected individuals • Roman Numerals (I – IV) are generations • Lines across represent mating • Lines down represent offspring

50. Understanding the Pedigree • Count the number of affected males and affected females. If most males and few or no females most likely sex linked trait. • Look at the affected individuals. If every individual with the trait has a parent with the trait then this trait is dominant. If non-affected parents produce an offspring with the trait then it is recessive. • Determine the phenotype and genotype of every individual