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Introduction to Genetics

Introduction to Genetics. The work of Gregor Mendel. Gregor Mendel. Austrian monk (1822-1844) Considered the father of modern genetics Carried out genetic experiments with ordinary garden peas. He knew that: Male parts of a flower produced pollen:

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Introduction to Genetics

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  1. Introduction to Genetics The work of Gregor Mendel

  2. Gregor Mendel • Austrian monk (1822-1844) • Considered the father of modern genetics • Carried out genetic experiments with ordinary garden peas. • He knew that: • Male parts of a flower produced pollen: • Contains sperm:male reproductive cells • Female portions of a flower produce eggs • Female reproductive cells.

  3. Pics (peas)

  4. Fertilization • Sexual reproduction: the male & female reproductive cells join together. • Fertilization produces a new cell – • Develops into a tiny embryo

  5. Pea plants • Pea plants are usually self -pollinating Sperm cells in pollen fertilize eggs in the same flower The seed has the same parent

  6. What kind of plants are these? • Same parent: True breeding • If these plants breed with themselves (self-pollinate): • Offspring would be identical to parent. • One stock of plants would: • Produce only tall plants , another only short • Produce only green seeds , another one only yellow. Cross - pollinating: male and female reproductive cells from different plants

  7. Traits: specific characteristics • Seed color: yellow or green • Seed shape: smooth or wrinkled

  8. round yellow gray Smooth Green Axial short

  9. Mendel’s Seven F1 crosses on Pea Plants. Round or wrinkled Yellow or green color peas Purple or white petals Smooth or wrinkled Green or yellow pods Long or short stems Axel or terminal flowers

  10. Mendel made 2 conclusions: I. Biological inheritance is passed on from one generation to the next through genes. • Traits occurred in two different forms (or more) and were expressed through alleles • Example: • One gene for yellow peas (alleles) • One gene for green peas (alleles)

  11. And also: • II. Principal of dominance: • Some alleles are dominant and others are recessive. • Phenotype: visible traits (dominant or recessive trait) • Genotype: present but not visible (recessive trait)

  12. Blue eyes – brown eyes

  13. Alleles

  14. Following the Generations Results in all Hybrids(Tt) Cross 2 Hybridsget3 Tall & 1 Short(TT, Tt, tt) Cross 2 Pure Plants(TT x tt)

  15. “P” : parent generation (true breeding) • Crossed a tall plant with a short plant. • F1 generation: the result of the “P” cross breeding. (F1 is a hybrid generation) • Here the tall gene is dominant and the short gene is recessive. • F2 generation: the result of the F1 self pollination. • ¼ of plants are short.

  16. Segregation • Remember: • Alleles for tall height is dominant • Alleles for short height is recessive • Each F1 plant produces two types of gametes (sex cells) • Those with the allele for tallness • Those with the allele for shortness

  17. Probability and Punnet Squares

  18. Probability • This is the likelihood that a particular event will occur. • If you flip a coin 3 times in a row , What is the probability that it will land head up every time? • ½ * ½ * ½ = 1/8. You have a 1 chance in 8 of flipping head 3 times in a row.

  19. Punnet Square. • Used to predict and compare the genetic variation from a cross. • T = dominant (tall) • t = recessive (short) • TT or tt : homozygous – two identical alleles for a particular trait. • Tt : heterozygous – two different alleles for the same trait.

  20. Phenotype & genotype • Phenotype: • physical characteristics ( can be a dominant or recessive gene) • Genotype: • genetic makeup (always recessive)

  21. Monohybrid Crosses

  22. P1 Monohybrid Cross • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: RoundseedsxWrinkled seeds • RRx rr Genotype:Rr Phenotype:Round GenotypicRatio:All alike PhenotypicRatio: All alike r r Rr Rr R R Rr Rr

  23. F1 Monohybrid Cross • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: Roundseeds xRound seeds • Rrx Rr Genotype:RR, Rr, rr Phenotype:Round & wrinkled G.Ratio:1:2:1 P.Ratio: 3:1 R r RR Rr R r Rr rr

  24. F2 Monohybrid Cross (1st) • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: RoundseedsxRound seeds • RRx Rr Genotype:RR, Rr Phenotype:Round GenotypicRatio:1:1 PhenotypicRatio: All alike R r RR Rr R R RR Rr

  25. F2 Monohybrid Cross (2nd) • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: WrinkledseedsxRound seeds • rrx Rr R r Genotype:Rr, rr Phenotype:Round & Wrinkled G. Ratio:1:1 P.Ratio: 1:1 Rr rr r r Rr rr

  26. 1 trait: height (tall or short) Tt Tt Tt (25%) TT (25%) Tt (25%) tt (25%) Figure 11-7 , p.268

  27. Illustrative example • A punnet square depicting a cross between two plants: • heterozygous for : purple (B) and white (b) blossoms.

  28. Results of Monohybrid Crosses • Inheritablefactors or genesare responsible for all heritable characteristics • Phenotype is based on Genotype • Each traitis based ontwo genes, one from the mother and the other from the father • True-breeding individuals are homozygous ( both alleles) are the same

  29. Mendel’s Laws

  30. Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. All the offspring will be heterozygous and express only the dominant trait. RR x rr yields all Rr (round seeds)

  31. Law of Dominance

  32. Law of Segregation • During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. • Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

  33. Applying the Law of Segregation

  34. Law of Independent Assortment • Alleles for differenttraits are distributed to sex cells (& offspring) independently of one another. • This law can be illustrated using dihybrid crosses.

  35. Dihybrid Cross • A breeding experiment that tracks the inheritance of two traits. • Mendel’s “Law of Independent Assortment” • a. Each pair of alleles segregates independently during gamete formation • b. Formula: 2n (n = # of heterozygotes)

  36. How many gametes will be produced for the following allele arrangements? • Remember:2n (n = # of heterozygotes) • 1. RrYy • 2. AaBbCCDd • 3. MmNnOoPPQQRrssTtQq

  37. Answer: 1. RrYy: 2n = 22 = 4 gametes RY Ry rY ry 2. AaBbCCDd: 2n = 23 = 8 gametes ABCD ABCd AbCD AbCd aBCD aBCd abCD abCD 3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64 gametes

  38. Dihybrid Cross • Traits: Seed shape & Seed color • Alleles:R round r wrinkled Y yellow y green RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations

  39. RY Ry rY ry RY Ry rY ry Dihybrid Cross

  40. RY Ry rY ry Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy 9:3:3:1 phenotypic ratio Dihybrid Cross

  41. Dihybrid Cross Round/Yellow: 9Round/green: 3wrinkled/Yellow: 3wrinkled/green: 1 9:3:3:1

  42. RRYy RrYY RrYy RRYy RRyy RrYy Rryy rrYY rrYy RrYY RrYy RrYy Rryy rryy rrYy F2 Generation

  43. Summary of Mendel’s principals • Inheritance of biological characteristics is passed from parent to offs spring (via genes) • Some forms of gene are dominate and other recessive • Adult organisms will have two copies of each gene – one from each parent • Alleles for different genes will (usually) segregate independently from each other.

  44. Non-Mendelian inheritance

  45. Incomplete DominanceandCodominance, sex-linked traits

  46. Incomplete dominance • The phenotype (appearance) of the offspring is intermediate. • neither allele of the pair is completely dominant. • They blend !!!!!!

  47. Homozygous Red Flower All 1st Generation Offspring Pink Flower Homozygous White Flower X =

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