Chapter 6

1. Chapter 6 DNA DetectiveComplex Patterns of Inheritance, and DNA Fingerprinting 0

2. 1 Extensions of Mendelian Genetics Incomplete Dominance is when a heterozygote expresses a phenotype intermediate between both alleles. For example, RR produces red flowers, Rr produces pink flowers and rr produces white flowers Codominance is when two alleles are expressed at the same time. ABO blood type is an example of this with both the dominant A and B being expressed in a type AB person. Multiple allelism occurs when there are more than two alleles of a gene. ABO blood types exhibit this.

3. 1 Extensions of Mendelian Genetics ABO blood group has three alleles of one gene: IAand IB are codominant to each other; i is recessive to both other alleles. An individual will have two of these alleles.

4. 1 Extensions of Mendelian Genetics Another blood group is called the Rh factor. Rh+ is caused by a dominant allele. Rh+Rh+ or Rh+Rh- Rh- is caused by 2 recessive alleles. Rh-Rh- Blood typing can be used to exclude potential parents. E.g., an AB parent can never have an O child and two Rh- parents can never have a Rh+ child. See Table 8.2 for compatibilities of blood types.

5. 1 Extensions of Mendelian Genetics Pleiotropy is the ability of a single gene to cause multiple effects on the individual’s phenotype. Hemophilia is an example of pleiotropy. The inability to clot blood normally due to the absence of a clotting factor Gene for this clotting factor is on the X chromosome Prince Alexis suffered from this and inherited the hemophilia allele from his mother

6. 2 Sex Determination and Sex Linkage Humans have 22 pairs of autosomes and one pair of sex chromosomes Women: two X chromosomes Men: one X and one Y chromosome

7. 2 Sex Determination and Sex Linkage Sex-linked genes: genes located on the sex chromosomes X-linked: located on the X chromosome Y-linked: located on the Y chromosome SRY gene which leads to the development of the testes Males always inherit their X from their mother Males are more likely to express recessive X-linked traits than females due to carrying only 1 X. Females are less likely to express X-linked traits since they have to have 2 copies of the bad X’s.

8. 2 Sex Determination and Sex Linkage • Only females can be carriers of X-linked recessive traits. • Carriers express the normal trait but are heterozygous, so they carry the allele for the recessive trait. • Hemophilia, red-green color blindness, and Duchenne Muscular dystrophy are example of X-linked traits.

9. 2 Sex Determination and Sex Linkage X inactivation guarantees that all females receive only 1 dose of the proteins by the X chromosomes. Inactivation is irreversible and inherited during cell division. It is caused by RNA wrapping around the X chromosome.

10. Animation: X-Linked Recessive Traits Click “Go to Animation” / Click “Play”

11. 3 Pedigrees Pedigree: a family tree, showing the inheritance of traits through several generations Symbols commonly used in pedigrees are circles and squares

12. 3 Pedigrees Pedigrees reveal modes of inheritance Pedigree for an autosomal dominant trait:

13. 3 Pedigrees Pedigree for an autosomal recessive trait:

14. 3 Pedigrees Pedigree for an X-linked trait:

15. 3 Pedigrees

16. 4 DNA Fingerprinting No two individuals are genetically identical except for identical twins. Small differences in nucleotide sequences of their DNA This is the basis for DNA fingerprinting Unambiguous identification of people When sample size is small it is necessary to copy the genetic material to increase the quantity available for testing.

17. 4 DNA Fingerprinting Small amounts of DNA can be amplified using PCR (polymerase chain reaction) DNA is mixed with nucleotides, specific primers, Taq polymerase, and then is heated Heating splits the DNA molecules into two complementary strands Taq polymerase builds a new complementary strand DNA is heated again, splitting the DNA and starting a new cycle.

18. 4 DNA Fingerprinting Each cycle, the amount of DNA doubles.

19. Animation: Polymerase Chain Reaction (PCR) Click “Go to Animation” / Click “Play”

20. 4 DNA Fingerprinting DNA is cut into fragments using restriction enzymes, which cut around DNA sequences called VNTRs (variable number tandem repeats).

21. 4 DNA Fingerprinting Gel electrophoresisseparates DNA fragments on basis of their sizes Electric current is applied to an agarose gel Smaller fragments run faster through the gel Fragments are transferred to a sheet of filter paper Labeled probe reveals locations of fragments containing VNTRs

22. 4 DNA Fingerprinting Each person’s set of fragments is unique. All of a child’s bands must be present in one or both of the parents.

23. 4 DNA Fingerprinting Pedigree of Romanov family

24. 4 DNA Fingerprinting To see if parents and their children were Romanovs, DNA fingerprints were prepared for relatives of tsar and tsarina. Adult male skeleton (related to the children) was related to George, the tsar’s brother. Adult female skeleton (related to the children) was related to Prince Philip, the tsarina’s grand-nephew. Conclusion: the grave contained the tsar, tsarina, three of their children, and four servants.

25. Which forensic technique was used to determine the identity of the Romanovs? examining fingerprints ballistic (firearm) evidence DNA fingerprinting toxicology

26. Which forensic technique was used to determine the identity of the Romanovs? examining fingerprints ballistic (firearm) evidence DNA fingerprinting toxicology

27. Snapdragon color is an example of incomplete dominance. If you cross a red snapdragon with a white snapdragon, what will the offspring look like? All of the offspring will be red. All of the offspring will be white. All of the offspring will be pink. Half the offspring will be red and half will be white.

28. Snapdragon color is an example of incomplete dominance. If you cross a red snapdragon with a white snapdragon, what will the offspring look like? All of the offspring will be red. All of the offspring will be white. All of the offspring will be pink. Half the offspring will be red and half will be white.

29. Coat color of cattle displays codominance. A red coated cattle is bred with a white coated cattle. What color coat will their offspring have? Red coat C. Pink coat White coat D. Red and white coat

30. Coat color of cattle displays codominance. A red coated cattle is bred with a white coated cattle. What color coat will their offspring have? Red coat C. Pink coat White coat D.Red and white coat

31. Which genetic term best describes how the ABO blood system is inherited? codominance incomplete dominance pleiotropy X-inactivation

32. Which genetic term best describes how the ABO blood system is inherited? codominance incomplete dominance pleiotropy X-inactivation

33. Who is more likely to suffer from colorblindness, a disorder caused by a recessive allele on the X-chromosome? males females babies the elderly

34. Who is more likely to suffer from colorblindness, a disorder caused by a recessive allele on the X-chromosome? males females babies the elderly

35. Which of the following disorders is carried on the X chromosome and is considered pleiotrophic? Huntington's disease Cystic Fibrosis Hemophilia Tay-Sachs

36. Which of the following disorders is carried on the X chromosome and is considered pleiotrophic? Huntington's disease Cystic Fibrosis Hemophilia Tay-Sachs

37. What type of trait does this pedigree show? recessive trait sex-linked trait dominant trait codominant trait

38. What type of trait does this pedigree show? recessive trait sex-linked trait dominant trait codominant trait

39. Why is Taq polymerase used instead of human DNA polymerase? Taq polymerase is resistant to high temperatures. Taq polymerase is resistant to high pH levels. Taq polymerase is resistant to low temperatures. Taq polymerase is resistant to low pH levels.

40. Why is Taq polymerase used instead of human DNA polymerase? Taq polymerase is resistant to high temperatures. Taq polymerase is resistant to high pH levels. Taq polymerase is resistant to low temperatures. Taq polymerase is resistant to low pH levels.

41. Gel electrophoresis separates DNA fragments based on _______. Shape pH Number of strands Size

42. Gel electrophoresis separates DNA fragments based on _______. Shape pH Number of strands Size

43. ______ is used to amplify DNA. PCR Gel electrophoresis RFLP VNTR

44. ______ is used to amplify DNA. PCR Gel electrophoresis RFLP VNTR