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Biology 2250 Principles of Genetics

Biology 2250 Principles of Genetics. Announcements Lab 3 Information: B2250 (Innes) webpage download and print before lab. Virtual fly: log in and practice http://biologylab.awlonline.com/

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Biology 2250 Principles of Genetics

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  1. Biology 2250Principles of Genetics Announcements Lab 3 Information: B2250 (Innes) webpage download and print before lab. Virtual fly: log in and practice http://biologylab.awlonline.com/ people that have ALREADY picked up their exams should see Dr. Carr for a re-marking of p. 2

  2. Weekly Online Quizzes Marks Oct. 14 - Oct. 25 Example Quiz 2** for logging in Oct. 21- Oct. 25 Quiz 1 2 Oct. 28 Quiz 2 2 Nov. 4 Quiz 3 2 Nov. 10 Quiz 4 2

  3. B2250Readings and Problems Ch. 4 p. 100 – 112 Prob: 10, 11, 12, 18, 19 Ch. 5 p. 118 – 129 Prob: 1 – 3, 5, 6, 7, 8, 9 Ch. 6 p. 148 – 165 Prob: 1, 2, 3, 10

  4. Mendelian Genetics    Topics: -Transmission of DNA during cell division Mitosis and Meiosis - Segregation - Sex linkage (problem: how to get a white-eyed female) - Inheritance and probability - Independent Assortment - Mendelian genetics in humans - Linkage - Gene mapping   - Tetrad Analysis (mapping in fungi) - Extensions to Mendelian Genetics - Gene mutation - Chromosome mutation - Quantitative and population genetics

  5. Mendelian Inheritance Determining mode of inheritance: - single gene or more complicated - recessive or dominant - sex linked or autosomal Approach: cross parents observed progeny compare with expected

  6. Mendel’s First Law ½ A gametes Aa Meiosis: diploid nucleus divides produces haploid nuclei Equal segregation of two members of a gene pair ½ a gametes P(a) = ½ P(A) = ½

  7. Mendel’s Second Law Independent assortment: during gamete formation, the segregation of one gene pair is independent of other gene pairs.

  8. Two Characters Monohybrid Cross parents differ for a single character (single gene ); seed shape Dihybrid Cross parents differ for two characteristics (two genes)

  9. Dihybrid Two Characters: 1. Seed colour yellowgreen Yy 2. Seed shape Round wrinkled Rr 4 phenotypes

  10. Dihybrid P Gametes RRyy X rrYY Ry rY RrYy DIHYBRID F1

  11. F1 Dihybrid ----->F2 F1 RrYy RrYy X RrYy F2 9 315 round, yellow 3 108 round, green 3 101 wrinkled, yellow 1 32 wrinkled, green Total 556

  12. Producing the F2 F1 YyRr X YyRr 1. F1 Gametes produce F2 2. Genotypes 3. Phenotypes F2

  13. Independent Assortment Male gametes Two gene systems: 1. Gametes from dihybrid 4 x 4 = 16 YyRr: ¼ YR Yr yR yr ¼ YR1/16YYRR Yr yR yr Female gametes F2

  14. Independent Assortment YyRr X YyRr 2. F2 Genotypes 3 x 3 = 9 ¼ RR ½ Rr ¼ rr ¼ YY1/16 YYRR ½ Yy ¼ yy F2

  15. Independent Assortment YyRr X YyRr 3. F2 Phenotypes 2 x 2 = 4 ¾ R- ¼ rr ¾ Y-9/16 R-Y- ¼ yy

  16. F1 YyRr x YyRr YY RR YY Rr Y-R- Yy RR Yy Rr YY rr Y-rr Yy rr yy RR yyR- yy Rr yyrr yy rr 9 Genotypes 4 phenotypes

  17. Independent Assortment Any number of independent genes: Genes Phenotypes Genotypes 1 2 3 2 4 (2 x2) 9 (3 x 3) 3 8 (2x2x2) 27 (3 x 3 x 3) n 2n 3n

  18. Mendelian Genetics in Humans Determining mode of inheritance Problems: 1. long generation time 2. can not control mating Alternative: * information from matings that have already occurred “Pedigree”

  19. Human Pedigrees Pedigree analysis: trace inheritance of disease or condition provide clues for mode of inheritance (dominant vs. recessive) (autosomal vs. sex linked) however, some pedigrees ambiguous

  20. Human Pedigrees 1. Ambiguous: 2. Unambiguous: Normal female Normal male Affected female

  21. Clues (non sex-linked) Recessive: 1. individual expressing trait has two normal parents 2. two affected parents can not have an unaffected child.

  22. Rare Recessive Rare = AA A- (AA or Aa) Cousins (inbreeding)

  23. Clues Dominant: 1. every affected person has at least one affected parent 2. each generation will have affected individuals

  24. Dominant Not AA All genotypes known

  25. Examples Recessive: - phenylketonuria (PKU) - hemophilia (sex linked) - cystic fibrosis - albinism Dominant: - huntingtons chorea - brachydactyly (short fingers) - polydactyly (extra fingers) - achondroblasia (dwarf)

  26. 2n = 46 http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=OMIM

  27. Brachydactyly Bb bb Bb short fingers bb normal

  28. http://omia.angis.org.au/

  29. Online Tutorial: http://www.biology.arizona.edu/mendelian_genetics/mendelian_genetics.html

  30. Solving Genetics Problems Don’t panic! Carefully read the problem What information is given? Know the terms used. What aspect of genetics does the problem address?

  31. Sex Linked Inheritance X-linked Dominant 1. affected male ---> all daughters affected no sons aa x AY ----> Aa, aY 2. affected female ----> ½ sons, ½ daughters affected Aa x aY ----> AY, aY, aa, Aa * *

  32. X-Linked Dominant 1. All daughters affected, no sons 2. 1/2 daughters affected, 1/2 sons affected

  33. X-linked Inheritance X-linked recessive: 1. more males than females show recessive phenotype 2. affected female ------> both mother and father have recessive allele A a x a Y --------> a a

  34. X-linked Inheritance X-linked recessive: 3. affected male ----> mother carries allele A a x AY -----> a Y 4. affected male -----> no affected offspring AA x a Y ----> AY, Aa carrier carrier

  35. X-Linked Recessive Mother carrier

  36. Sex Linked Inheritance(examples) X linked genes Humans: - colour blindness - hemophilia More common in males (hemizygous aY) X linked recessives expressed

  37. Queen Victoria (carrier) QE II Hemophilic male Carrier female X-linked recessive hemophilia

  38. X – linked disease genes

  39. Mendelian Genetics Topics: -Transmission of DNA during cell division Mitosis and Meiosis - Segregation (Monohybrid) - Sex linkage - Inheritance and probability - Independent Assortment (Dihybrid) - Mendelian genetics in humans (Pedigree)

  40. Mendel’s Second Law Independent assortment: during gamete formation, the segregation of one gene pair is independent of other gene pairs. Genes independent because they are on different chromosomes

  41. Independent Assortment Genotypes AABB AaBb AaBB AABb F1 AaBb X AaBb F2 9 A-B- 3 A-bb 3 aaB- 1 aabb Aabb, AAbb 4 phenotypes aaBb, aaBB

  42. Independent Assortment Test Cross AaBb X aabb gametes ab 1/4 AB AaBb 1/4 Ab Aabb 1/4 aB aaBb 1/4 ab aabb 4 phenotypes 4 genotypes

  43. Independent Assortment Inferred F1 gamete types AB Fig 6-6 ab Ab aB Interchromosomal Recombination

  44. (Genes) Meiosis I A Correlation of genes and Chromosomes during meiosis a 4 gamete types b B A A OR a a b B

  45. Linkage of Genes - Many more genes than chromosomes - Some genes must be linked on the same chromosome; therefore not independent

  46. Complete Linkage X dihybrid P A B a b F1 A B a b AaBb F1 gametes A B AB Parental Parental a b ab

  47. Recombinant Gametes ? Crossing over: - exchange between homologous chromosomes

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