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Mendel and the Gene Idea

Mendel and the Gene Idea. Chp 14. Blending Model vs. Particulate Model. Discreet inheritable units Traits retain separate identities. genetic material mixes like paint Parent’s traits inseparable. Figure 14-01. Gregor Mendel. Austrian Monk

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Mendel and the Gene Idea

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  1. Mendel and the Gene Idea Chp 14

  2. Blending Model vs. Particulate Model • Discreet inheritable units • Traits retain separate identities • genetic material mixes like paint • Parent’s traits inseparable

  3. Figure 14-01 Gregor Mendel • Austrian Monk • Did not know about DNA, genes, or chromosomes! • Tried to prove particulate model of inheritance using pea plants Web Lab: Mendel and his Peas

  4. Advantages of working with pea plants: • Many different varieties • Character = inheritable feature (GENE) • Trait = variation of that character (ALLELE) • Can control plant matings (paintbrush)

  5. Removed stamens from purple flower Transferred sperm- bearing pollen from stamens of white flower to egg- bearing carpel of purple flower LE 14-2 Parental generation (P) Stamens Carpel Pollinated carpel matured into pod Planted seeds from pod Examined offspring: all purple flowers First generation offspring (F1)

  6. Started with true-breeding varieties = HOMOZYGOUS • If allowed to self-pollinate, all offspring had the same traits as their parent plant • Then, cross-pollinated two different true-breeding varieties = HYBRIDIZATION

  7. Hybridization

  8. P Generation LE 14-5_1 Appearance: Purple flowers PP White flowers pp Genetic makeup: Gametes: p P F1 Generation hybrid Appearance: Genetic makeup: Purple flowers Pp Monohybrid Cross – tracks a single character/gene

  9. Mendel’s Law of Segregation: Parental alleles separate (segregate) during gamete formation • occurs in Metaphase I of Meiosis I • only one allele per gamete

  10. P Generation Purple flowers PP White flowers pp Appearance: LE 14-5_2 Genetic makeup: p P Gametes F1 Generation Appearance: Genetic makeup: Purple flowers Pp gametes Gametes: 1 1 p P 2 2 F1 sperm P p F2 Generation Punnett Square showspossible offspring after fertilization P PP Pp gametes F1 eggs p Pp pp 3 : 1

  11. Genotype Phenotype PP (homozygous Purple 1 LE 14-6 Pp (heterozygous 3 Purple 2 Pp (heterozygous Purple pp (homozygous White 1 1 Ratio 1:2:1 Ratio 3:1

  12. r R F1 Rr r R F2 Rr rr Rr 3 round: 1 wrinkled 1 RR : 2 Rr : 1 rr

  13. Law of Dominance: The dominant allele (trait) is fully expressed and the recessive allele has no noticeable effect Recessive ≠ Bad

  14. Test Cross • Used to determine the genotype of an individual with a dominant phenotype • Cross it with a homozygous recessive and observe offspring ratios

  15. 100% tall 100% Tt 1 tall : 1 dwarf 1 Tt : 1 tt T T t T tt Tt Tt Tt t t Tt tt Tt Tt t t

  16. Law of Independent Assortment: Each allele pair segregates independently of other allele pairs during Meiosis (Metaphase I).

  17. Dihybrid Cross: tracks two genes (characters)

  18. TP tP tp Tp TTPp TTPP TtPp TtPP TP Tall purple Tp TTPp Ttpp TtPp TTpp TtPp ttPp tP ttPP TtPp TtPP TP Tp tP tp TtPp tp Ttpp ttPp ttpp 9 tall purple 3 dwarf purple 1 dwarf white 3 tall white 12:4 or 3:1 12:4 or 3:1

  19. Probability ranges from 0 – 1 Rule of Multiplication: Used to determine the chance of two or more independent events occurring together Determine probability of each independent event Multiply probabilities together Ex: What is the probability (chance) that when 2 coins are flipped they will both end up heads? Rules of Probability & Genetics ½ x ½ = ¼ (or .25)

  20. ½ ½ ½ ¼ ¼ ½ ¼ ¼

  21. What is the probability (chance) that 2 dice will both show a 4 when rolled? 1/6 x 1/6 = 1/36 Multiplication RuleProbability Problems

  22. Ex (F1): T t P p x T t P p F2: t p t p ½ x ½ x ½ x ½ = 1/16 t t p p ½ ½ ½ ½

  23. What is the probability (chance) that the sum of the numbers shown on 2 dice will equal 5? Rule of Addition: used to determine the probability of an event that can occur in two or more different ways/combinations Calculate probability for each possible combination/way using Rule of Multiplication Add the probabilities for each separate combination to get the total probability Rule of Addition

  24. What is the probability (chance) that the sum of the numbers shown on 2 dice will equal 5? Possible combinations: 1 + 4 2 + 3 3 + 2 4 + 1 1/6 x 1/6 1/6 x 1/61/6 x 1/61/6 x 1/6 1/36 +1/36 +1/36 +1/36 = 4/36 ( 1/9 ) Rule of Addition

  25. = 3/8 1 x x ½ ¾

  26. A__ B__ C__ = A__ B__ c c = A__ b b C__ = a a B__ C__ =

  27. A__ B__ C__ = 3/8 A__ B__ c c = 0 A__ b b C__ = 3/8 a a B__ C__ = 1/8 Sum = 7/8

  28. All problems (#1-17) due on Tonight, work on problems: # 2, 3, 4, 7, 8, & 10 Text book: pages 272 - 273

  29. Complete Dominance – one allele complete masks the other; the heterozygous (Rr) and homozygous dominant (RR) have the same phenotype Types of Dominance • The dominant allele usually codes for some protein/enzyme and the recessive allele codes for a defective protein/enzyme. Both are “expressed”, but only the dominant allele is functional and observable

  30. Codominance = two alleles expressed separately & both affect phenotype Ex: Red & White rhododendron “Roan” color in cattle Types of Dominance

  31. Incomplete Dominance = F1 hybrids (heterozygotes) have an intermediate phenotype Results in a THIRD phenotype NOT the same as blending (F2 show all phenotypes) 1:2:1 phenotypic and genotypic ratios in F2 Types of Dominance

  32. Multiple Alleles = more than two alleles/varieties IA & IB are codominant over i Fill in Interactive Question 14.6

  33. Suppose a father of blood type B and a mother of blood type A have a child of type O. What are the chances that their next child will be: Type O? Type B? Type A? Type AB? Blood Type practice…

  34. Blood Type practice… • Suppose a father of blood type B and a mother of blood type A have a child of type O. What are the chances that their next child will be: • Type O? ¼ • Type B? ¼ • Type A? ¼ • Type AB? ¼

  35. Pleiotropy = one gene has multiple phenotypic effects Ex: cystic fibrosis & sickle-cell disease Pleiotropy

  36. Epistasis = (“force upon”) one gene affects the expression of another gene Ex: coat color in mice BbCc BbCc Sperm bC Bc 1 1 1 1 BC bc 4 4 4 4 1 BC BBCC BbCC BBCc BbCc 4 1 bC BbCC bbCC BbCc bbCc 4 BBcc Bbcc BBCc BbCc 1 Bc 4 bbcc Bbcc 1 bbCc bc BbCc 4 9 3 4 16 16 16

  37. ¾ * ¾ = 9/16 M__B__ ¾ * ¼ = 3/16 brown white mm __ __ ¼ * 1 = 4/16 (¼)

  38. Polygenic = additive effect of 2 or more genes on one phenotype Ex: skin color height AaBbCc AaBbCc aabbcc Aabbcc AaBbcc AaBbCc AABbCc AABBCc AABBCC 20/64 15/64 Fraction of progeny 6/64 # alleles + 1 = # phenotypes 1/64

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