Download
chapter 11 part 2 n.
Skip this Video
Loading SlideShow in 5 Seconds..
Chapter 11 (Part 2) PowerPoint Presentation
Download Presentation
Chapter 11 (Part 2)

Chapter 11 (Part 2)

157 Vues Download Presentation
Télécharger la présentation

Chapter 11 (Part 2)

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Chapter 11 (Part 2) Punnett Squares Honors Genetics Ms. Gaynor

  2. What is “Probability”? • Why did Mendel get his results? • What is the probability that Mendel would get his results EACH time? • PROBABILITY = likelihood (chance) that an event will happen

  3. Probability Rules Probability Rule #1 The multiplication rule (“and”) • States that the probability that 2 or more independent events will occur together is the product (x ing) of their individual probabilities

  4. Rr Segregation of alleles into eggs Rr Segregation of alleles into sperm   Sperm r R 1⁄2 1⁄2 R R r R R 1⁄2 1⁄4 1⁄4 Eggs r r R r r 1⁄2 1⁄4 1⁄4

  5. Probability Rule #2 • The rule of addition (“or”) • States that the probability that any 1 of 2 or more exclusive events will occur is calculated by adding (+ ing) together their individual probabilities

  6. IN SUMMARY:2 Probability Rules Multiplication Rule • What are the chances of _?_AND_?_ happening at the same time? • MULTIPLY probability of EACH event happening TOGETHER Addition Rule • What are the chances of _?_ OR_?_ happening at same time? • ADD the probability of EACH event happening TOGETHER

  7. Probability Example Problems • Ms. Gaynor has 4 sisters. What is the probability that this will happen (her mother having 5 girls in a row)? • ½ x ½ x ½ x ½ x ½ =?? • 0.03125 or 3.125 % chance

  8. Mendel’s Results • Does Mendel’s segregation model account for the 3:1 ratio he observed in the F2 generation of his numerous crosses? • We can answer this question using a Punnett square, which shows a genetic cross

  9. What is a Punnett Square? • a diagram (box) used to predict the probabilities of the possible outcomes for offspring that will result from a cross between 2 parents • SHOWS EXPECTED RESULTS (not necessarily actual)

  10. Monohybrid Cross • a cross between 2 individuals that looks at 1 trait • There are 4 different types • Ex: freckles OR dimples • a cross between 2 individuals that looks at the possibilities of inheriting 2 DIFFERENT traits at one time • Ex: Freckles AND dimples Dihybrid Cross

  11. Monohybrid Punnett Square Mom’s genotype (Hh) x Dad’s genotype (hh) Tall Short Mom’s allele #1 Mom’s allele #2 H h Dad’s Allele #1 h Dad’s Allele #2 h

  12. Genotypic Ratio vs. Phenotypic Ratio • Genotypic Ratio = the GENOTYPE probabilities (expected results) of offspring • Ex: 50 % AA and 50 % Aa • Phenotypic Ratio = the PHENOTYPE probabilities (expected results) of offspring • Ex: 100% Tall

  13. Ratios • Can be expressed as a: • DECIMAL • Ex: 0.75 and 0.25 • FRACTION • Ex: ¾ and ¼ • PRECENTAGE • Ex: 75% and 25% • RATIO • Ex: 3: 1

  14. Punnett Square Genotypic ratio = 50 % Hh, 50% hh Phenotypic ratio = 50 % Tall, 50% short

  15. COMPLETE DOMINANCE: 4 different types of monohybrid crosses

  16. #1: Homozygous Dominant x Homozygous Recessive Mom’s genotype (HH) x Dad’s genotype (hh) Tall Short H H h h Genotypic ratio = 100% Hh (4:0) Phenotypic ratio = 100% Tall (4:0)

  17. #2: Homozygous Recessive x Homozygous Recessive Mom’s genotype (hh) x Dad’s genotype (hh) short Short h h h h Genotypic ratio = 100% hh (4:0) Phenotypic ratio = 100% short (4:0)

  18. #3: Homozygous Dominant x Heterozygous Mom’s genotype (HH) x Dad’s genotype (Hh) Tall Tall H H H h Genotypic ratio = 50% HH, 50% Hh (2:2) Phenotypic ratio = 100% Tall (4:0)

  19. #4: Heterozygous x Heterozygous Mom’s genotype (Hh) x Dad’s genotype (Hh) Tall Tall H h H h Genotypic ratio = 25% HH, 50% Hh, 25% hh (1:2:1) Phenotypic ratio = 75% Tall, 25% short (3:1)

  20. Phenotype Genotype Purple PP (homozygous) 1 Pp (heterozygous) 3 Purple 2 Pp (heterozygous) Purple 1 pp (homozygous) White 1 Ratio 3:1 Ratio 1:2:1 Figure 14.6

  21. The Testcross • Allows us to determine the genotype of an organism with the dominant phenotype, but unknown genotype • Genotype is not immediately obvious • Cross an individual with the dominant phenotype with an individual that is homozygous recessive for a trait

  22. Conduct a test cross, where the unknown dominant individual is crossed with the known recessive . • H _ ?_ x hh

  23. Test Cross Mom’s genotype (H?) x Dad’s genotype (hh) Tall Short H ? h h Genetypic ratio = Phenotypic ratio =

  24. Mendel’s 2nd Law:Law of Independent Assortment • says that the genes are inherited independently of other genes • Occurs during Metaphase I • Mendel assumed traits occur on different chromosomes!

  25. Dihybrid Crosses • How are two characters transmitted from parents to offspring? • As a package? • Independently?

  26. Dihybrid Crosses • crosses involveing crossing 2 DIFFERENT traits at one time • Example: Mate 2 parents and look at the probability of seeing 2 traits, such as: • eye color AND hair color • freckles AND dimples • Produces four possible phenotypes in the F2 generation

  27. Using the information from a dihybrid cross, Mendel developed the law of independent assortment • Each pair of alleles segregates independently during gamete formation

  28. For the following genotype, how many DIFFERENT gametes can be formed? • AaBBCcDdeeFf • 10 different • A, a, B, C, c, D, d, e, F, f

  29. How do You Do Dihybrid Crosses? 2 ways 1. one BIG Punnett Square (16 boxes instead of 4) 2. Make 2 separate Punnett Squares • 1 square for EACH trait • Then use PROBABILITY RULES and MULTIPLY

  30. One BIG Punnett Square 1. Find the possible gametes using F.O.I.L method AaBb x AABb AB AB Ab Ab aB AB ab Ab

  31. 2. Place the gametes in the Punnett Square & fill in boxes AB Ab aB ab AB Ab AB Ab

  32. Genotypic Ratio AAbB = 8/16 or 1/2 AaBB = 2/16 or 1/8 Aabb = 2/16 or 1/8 AABB = 2/16 or 1/8 AAbb= 2/16 or 1/8

  33. Phenotypic Ratio A= freckles, a= no freckles B = Dimples, b= no dimples AAbB = 8/16 (50%) freckles, dimples AaBB = 2/16 (12.5%) freckles, dimples Aabb = 2/16 (12.5%) freckles, no dimples AABB= 2/16 (12.5%) freckles, dimples AAbb = 2/16 (12.5%) freckles, no dimples So…12/16 (75%) freckles AND dimples 4/16 (25%) freckles AND no dimples

  34. Now…the easier way! • Write out a key for EACH trait • AA, Aa= Freckles, aa= No freckles • BB, Bb= Dimples, bb= No dimples • Figure out the genotypes of EACH parent and put them together • Draw 2 Punnett squares & figure out the FRACTION ratio of possible genotype and phenotypes • Draw punnett square #1 for trait #1 • Draw punnett square #2 for trait #2 • Figure out genotype/phenotype possibilities of offspring by multiplying fractions

  35. The Laws of Probability Control Mendelian Inheritance • Mendel’s laws of segregation and independent assortment • Reflect the rules of probability

  36. Probability Rules and Dihybrid Crosses • A dihybrid or other multicharacter cross • Is equivalent to two or more independent monohybrid crosses occurring simultaneously • In calculating the chances for various genotypes from such crosses • Each character first is considered separately and then the individual probabilities are multiplied together