Human Patterns of Inheritance

1. Human Patterns of Inheritance Chapter 7

2. Human Patterns of Inheritance • *Complete Dominance - Mendel • Incomplete Dominance – Blending • Co-Dominance – 2 alleles expressed • Multiple Alleles – Blood Type • Polygenic Inheritance – height, hair, eyes • Epistasis • **Sex Linked Traits - X or Y

3. Humans are difficult to study… Why? • Each cell has ~30,000 different genes interacting; Exceptions to Mendel • Experimental & Investigative Problems • Long Generation Time • Small # of Offspring • Nature vs. Nurture

4. How do we know what we know? • Pedigrees • Twin Studies – nature vs. nurture • Human Genome Project – sequenced all genes • Unethical Studies in History • Genetic Technologies – DNA fingerprint, gene knockout, transgenic studies

5. Co-dominance – When both of the parent’s alleles are seen in a heterozygous child. Both equally expressed! Brown skin color allele (B) and white skin color allele (W) both expressed (BW) in phenotype

6. Co-Dominance A brown and white spotted cow (BW) is mated with a brown and white spotted cow (BW). What are the possible phenotypes of their offspring. Set up a punnett square. Genotypic ratio = 1 BB: 2BW: 1WW Phenotypic ratio = 1 Brown: 2 Brown/White:1 White

7. Incomplete Dominance – When neither of the parent’s traits are seen in a heterozygous offspring. Instead you see an intermediate trait (blending) Red allele (R) and White allele ( r) blend to make pink flowers – heterozygous condition

8. Incomplete Dominance Problem A pink snapdragon flower (Rr) is crossed with another pink snapdragon flower (Rr). What are the possible offspring colors? Set up a punnett square. Rr x Rr Phenotypic ratio = genotypic ratio Ratio = 1 red (RR) :2 pink (Rr) :1 white (rr)

9. Blood Typing – Multiple Alleles & Co Dom • More two alleles control a trait • not a mixing (like incomplete dom.) • BOTH alleles may be expressed (co-dominant) or exhibit complete dominance • Ex: Blood phenotypes type = A, B, AB, O • May write genotype AO or IAIO • A is dominant to O AA, AO  Type A • B is dominant to O BB, BO  Type B • A-B co-dominant AB  Type AB • O is recessive OO  Type O

10. ABO – antigen marker on blood cellDetermines antibody made (opposite)Why? Autoimmunity!

11. ABO - Example Problem • A person with genotype type AB blood and a person with phenotype O blood have a child. What are the possible blood types of the offspring? Work a punnett square. • Phenotype: A – 50% • Phenotype: B - 50% • A woman with type A blood is has a child with a man who has type B blood. Their child has type O blood. Was the child switched at birth? Explain.

12. Rh Factor - +/- • A second main trait for blood exists • Rh = protein on the surface of a red blood cell • Rh + means has protein/Rh- does not • Rh+ is dominant; Rh- is recessive

13. Blood types by percentage…Anything unusual? • O+: 38 percent • O-: 7 percent • A+: 34 percent • A-: 6 percent • B+: 9 percent • B-: 2 percent • AB+: 3 percent • AB-: 1 percent

14. Blood Typing is Important Because… • Transfusions - Red blood cells of incompatible blood types may clump together leading to death – (agglutination) • Rh (–) person cannot take Rh(+) blood • O- universal donor; AB+ universal recipient • Solve problems of unknown parentage. • Unable to say who definitely is the father, but can say who definitely isn’t the father.

15. Blood agglutination

16. ABO/Rh - Determining two factors for blood typing – use a DIHYBRID punnett square • A male with blood genotype AO+- has a child with a female blood genotype BO-- . • How do you find out probabilities of offspring? • Dihybrid punnett • Gametes: • Male: A+, A-, O+, O- • Female: B-, B-, O-,O-

17. Polygenic Inheritance • When a trait is controlled by 2 or more genes • AaBBCc • Explains the presence of multiple phenotypes for a single trait (Polymorphism) • Example: • Skin Color-if a darker skin and lighter skin individual produce offspring, the offspring will have an intermediate color of skin • Hair Color/Eye Color - there are approximately six genes that govern eye color, from brown to blue. • Height, nose length, and footsize to name a few…

18. Polymorphism – a widerange of trait values

19. I. Epistasis One gene controls the function of another gene Example: For example, in mice there is a gene that codes for the presence or absence of pigmentation in fur. A second gene codes for the color of the fur if pigmentation is present. If the first gene codes for the absence of pigmentation, the mouse will have white fur regardless of the color the second gene codes for.

20. Human Genetics Problems Answers • a. 50% • b. SS and ss • c. Heterozygous – 50%; Homozygous Dom. 50% • d. A or O • e. Charlie = AO; Women – Wendy or Susan • f. 50% • g. Both Keith & Wendy – BO and BO genotypes • h. see board- Russ 6/16 A+, 2/16 A-, 6/16 – B+, 2/16 B- • i. 1. – 165cm 2. yes 3. 180cm 4. no • j. blue – 6/16; brown – 6/16; red – 4/16

21. Have developed ways to approach the difficulties… • Pedigree analysis – family history for a particular trait See page 315-316 in whale book for example *Circles represent females *Squares represent males *White represents persons with a normal phenotype (NOT trait being tracked) *Shaded represents persons with the abnormal, recessive, or disease trait *Half shaded = heterozygous if trait is recessive, incomplete dominance, etc *Generations are numbered with Roman numerals *Individuals in a generation are numbered from left to right

22. Pedigrees (A sneak peak) • What information do pedigrees provide? • Pattern of inheritance of specific alleles • The members of a family who exhibit a specific phenotype • Makes it possible to find unknown genotypes

23. Figure 14.14 Pedigree analysis

24. Figure 14.16 Large families provide excellent case studies of human genetics

25. “Blue People of Appalachia” • Six generations after a French orphan named Martin Fugate settled on the banks of eastern Kentucky's Troublesome Creek with his redheaded American bride, his great-great-great great grandson was born in a modern hospital not far from where the creek still runs. • The boy inherited his father's lankiness and his mother's slightly nasal way of speaking. • What he got from Martin Fugate was dark blue skin. "It was almost purple," his father recalls. • Doctors were so astonished by the color of Benjy Stacy's skin that they raced him by ambulance from the maternity ward in the hospital near Hazard to a medical clinic in Lexington. Two days of tests produced no explanation for skin the color of a bruised plum. ….

26. “Blue People” Pedigree • A symptom of this condition is “blue skin” which is due to the absence of the enzyme diaforase, a necessary enzyme that converts methemoglobin to hemoglobin • Co-dominant trait – Bb - some blue, bb – very blue!

28. Huntington’s Pedigree Lab

29. What Determines Gender Anyway? • “Autosomes” – body chromosomes (1-22) • “Sex Chromosomes”-determine sex of an organism • The 23rd pair of chromosomes in humans (the last set) MaleFemale

30. People You Should Know… • E.B. Wilson and Nettie Stevens (1905)-American scientists who discovered sex chromosomes • In females, sex chromosomes match: XX • In males, sex chromosomes differ: XY • Punnett Square for determining gender:

31. How do we determine the sex/genetic disorders of a baby?Karyotyping! karyotype – picture of chromosomes • Can detect gender (XX or XY) • Can detect non-disjunction (ex: Down Syndrome, XYY Syndrome, Turner’s Syndrome, etc)

32. Figure 14.17 Testing a fetus for genetic disorders

35. Figure 15.14 Down syndrome

36. Figure 15.x3 XYY karyotype

37. Discovery of traits on the sex chromosomes… • Thomas Hunt Morgan (1912)- Showed that the presence of white eye color gene in fruit flies was located on the X chromosome. • P1 – white eye x red eye  100% red eyes • F1 – red eye x red eye  75% red; 25% white eyes • All white eyed flies were male! (XrY)

38. Figure 15.2 Morgan’s first mutant

39. Sex Linked Traits • Alleles are located on particular chromosomes • Trait is carried on a sex chromosome; exception to 2 allele/trait rule! • Most sex linked are on the X-chromosome • Y-linked-father  son • X-linked- mother  son, daughter; father  daughter Ex: colorblindess, hemophilia

40. X-linked Disorder

41. Section 14-2 • Write allele (ex: C or c) superscript next to chromosome that carries that allele (chromosome is inherited intact with allele) • Red-green colorblindness is an X-linked recessive trait • Carrier mother x normal male - XCXc x XCY Father (normal vision) Normal vision Colorblind Male Female Daughter (normal vision) Son (normal vision) Mother (carrier) Daughter (carrier) Son (colorblind) Go to Section:

42. Try this…. • Colorblindness is a recessive trait found on the X chromosome • A father (XC Y) and a colorblind mother (Xc Xc) mother have a female child and a male child. What is the probability either child will be colorblind. Work the punnett square.

43. Try this… • Boris is a hemophiliac (XhY) and Natasha is a normal (XH XH). Natasha is pregnant with a fraternal twins – a boy and a girl. • What are the chances that the boy will have hemophilia? • What are the chances the girl will have hemophilia? • What are the chances she will be a carrier?

44. What are the hallmarks of X-linked recessive inheritance? • As with any X-linked trait, the disease is never passed from father to son. • Males are much more likely to be affected than females. • All affected males in a family are related through their mothers. • Trait or disease is typically passed from an affected grandfather, through his carrier daughters, to half of his grandsons.

45. Hemophilia in the Royal Families

46. A little more on Red-Green Colorblindness (Protanopia) • Humans have 3 color receptors (wavelength receptors) – red, green and blue • All other shades are combinations of these colors interpreted by the ocular nerve’s impulse to the visual cortex of the brain • Red/Green colorblindess has altered cone proteins which perceive wavelengths of light

47. What # do you see in the middle?