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Genetics by Mendel

Genetics by Mendel. One gene with two alleles CONTROLING TWO contrasting / Alternative forms of a SPECIFIC TRAIT is called MendeLElian Genetics. Introduction. Genetics is the study of genes. Inheritance is how traits, or characteristics, are passed on from generation to generation.

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Genetics by Mendel

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  1. Genetics by Mendel One gene with twoalleles CONTROLING TWO contrasting/ Alternative forms of a SPECIFIC TRAIT is called MendeLElian Genetics

  2. Introduction • Genetics is the study of genes. • Inheritance is how traits, or characteristics, are passed on from generation to generation. • Chromosomes are made up of genes, which are made up of DNA. • Genetic material (genes,chromosomes, DNA) is found inside the nucleus of a cell. • Gregor Mendel is considered “The Father of Genetics“ • Mendel's work was not recognized until the turn of the 20th century

  3. Mendelian Genetics • Dominanttraits-traits that are expressed. • Recessivetraits-traits that are covered up. • Alleles-the different forms of a characteristic. • Punnett Squares-show how crosses are made. • Probability-the chances/ percentages that something will occur. • Genotype-the types of genes (Alleles) present. • Phenotype-what it looks like. • Homozygous-two of the same alleles. • Heterozygous-two different alleles.

  4. Genes • Alleles - two forms of a gene (dominant & recessive) • Dominant – ‘stronger’ of two genes expressed in the hybrid; represented byacapital letter (R) • Recessive - gene that shows up less often in a cross; represented by alower case letter (r)

  5. Gregor Mendel • Austrian Monk. • Experimented with “pea plants”. • Used pea plants because: • They were available • They reproduced quickly • They showed obvious differences in the traits Understood that there was something that carried traits from one generation to the next - “FACTOR”.

  6. Gregor Mendel(1822-1884) Father of genetics Responsible for the Laws governing Inheritance of Traits

  7. Mendel cont…… In the mid-1800s, the rules underlying patterns of inheritance were uncovered in a series of experiments performed by an Austrian monk named Gregor Mendel.

  8. Gregor Johann Mendel • Between 1856 and 1863, Mendel cultivated and tested some 28,000 pea plants • He found that the plants' offspring retained traits of the parents • Called the “Father of Genetics"

  9. Site of Gregor Mendel’s experimental garden in the Czech Republic

  10. Mendel's Plant Breeding Experiments Gregor Mendel was one of the first to apply an experimental approach to the question of inheritance. For seven years, Mendel bred pea plants and recorded inheritance patterns in the offspring. Particulate Hypothesis of Inheritance Parents pass on to their offspring separate and distinct factors (today called genes) that are responsible for inherited traits.

  11. Mendel’s Pea Plant Experiments

  12. Why peas,Pisum sativum? • Can be grown in a small area • Produce lots of offspring • Produce pure plants when allowed to self-pollinate several generations • Can be artificially cross-pollinated

  13. Reproduction in Flowering Plants • Pollen contains sperm • Produced by the stamen • Ovary contains eggs • Found inside the flower • Pollen carries sperm to the eggs for fertilisation • Self-fertilisation can occur in the same flower • Cross-fertilisation can occur between flowers

  14. Mendel’s Experimental Methods • Mendel hand-pollinated flowers using a paintbrush • He could snip the stamens to prevent self-pollination • Covered each flower with a cloth bag • He traced traits through the several generations

  15. How Mendel Began Mendel produced pure strains by allowing the plants to self-pollinate for several generations

  16. Mendel was fortunate he chose the Garden Pea • Mendel probably chose to work with peas because they are available in many varieties. • The use of peas also gave Mendel strict control over which plants mated. • Fortunately, the pea traits are distinct and were clearly contrasting.

  17. To test the particulate hypothesis, Mendel crossed true-breeding plants that had two distinct and contrasting traits—for example, purple or white flowers. What is meant by “true breeding?” Mendel cross-fertilized his plants by hand. Why is it important to control which plants would serve as the parents?

  18. For each monohybrid cross, Mendel cross-fertilized true-breeding plants that were different in just one character—in this case, flower color. He then allowed the hybrids (the F1 generation) to self-fertilize.

  19. Typical breeding experiment P generation (parental generation) F1 generation (first filial generation, the word filial from the Latin word for "son") are the hybrid offspring. Allowing these F1 hybrids to self-pollinate produces: F2 generation (second filial generation). It is the analysis of this that lead to an understanding of genetic crosses.

  20. Eight Pea Plant Traits WITH THEIR CONTRASTING ALLELES • Seed shape--- Round (R) or Wrinkled (r) • Seed Colour---- Yellow (Y) or  Green (y) • Pod Shape--- Smooth (S) or wrinkled (s) • Pod Colour---  Green (G) or Yellow (g) • Seed Coat Colour---Gray (G) or White (g) • Flower position---Axial (A) or Terminal (a) • Plant Height--- Tall (T) or Short (t) • Flower colour--- Purple (P) or white (p)

  21. Mendel studies seven characteristics in the garden pea

  22. : Statistics indicated a pattern.

  23. Mendel stated that physical traits are inherited as “particles” Mendel did not know that the “particles” were actually Chromosomes & DNA Particulate Inheritance

  24. Genetic Terminology • Trait - any characteristic that can be passed from parent to offspring • Heredity - passing of traits from parent to offspring • Genetics - study of heredity

  25. Types of Genetic Crosses • Monohybrid cross - cross involving a single traite.g. flower colour • Dihybrid cross - cross involving two traits e.g. flower colour & plant height

  26. Punnett Square Used to help solve genetics problems

  27. More Terminology • Genotype - gene combination for a trait(e.g. RR, Rr, rr) • Phenotype - the physical feature resulting from a genotype (e.g. red, white)

  28. Genotype & Phenotype in Flowers Genotype of alleles:R= red flowerr= yellow flower All genes occur in pairs, so 2alleles affect a characteristic Possible combinations are: GenotypesRRRrrr PhenotypesRED RED YELLOW

  29. Genotypes • Homozygousgenotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also calledpure  • Heterozygousgenotype - gene combination of one dominant & one recessive allele    (e.g. Rr); also calledhybrid

  30. Mendel’s Experimental Results

  31. The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled Mendel’s observed ratio was 2.96:1 The discrepancy is due to statistical error The larger the sample the more nearly the results approximate to the theoretical ratio (see seed colour) Did the observed ratio during the experiments match the theoretical ratio?

  32. Generations • Parental P1 Generation= the parental generation in a breeding experiment. • F1 generation= the first-generation offspring in a breeding experiment. (1st filial generation) • From breeding individuals from the P1 generation • F2 generation= the second-generation offspring in a breeding experiment. (2nd filial generation) • From breeding individuals from the F1 generation

  33. Following the Generations Cross 2 Pure PlantsTT x tt Results in all HybridsTt Cross 2 Hybridsget3 Tall & 1 ShortTT, Tt, tt

  34. Monohybrid Crosses

  35. 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 F1 R Rr Rr

  36. P1 Monohybrid SUMMARY • Homozygous dominant x Homozygous recessive • OffspringallHeterozygous(hybrids) • Offspring calledF1 generation • Genotypic & Phenotypic ratio isALL ALIKE

  37. F1 Monohybrid Cross • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: Heterozygous Roundseeds xRound seeds • RrxRr Genotype:RR, Rr, rr Phenotype:Round & wrinkled G.Ratio:1:2:1 P.Ratio: 3:1 R r RR Rr R F2 r Rr rr

  38. F1 Monohybrid SUMMARY • Heterozygous x heterozygous • Offspring:25% Homozygous dominantRR50% HeterozygousRr25% Homozygous Recessiverr • Offspring calledF2 generation • Genotypic ratio is1:2:1 • Phenotypic Ratio is 3:1

  39. What Do the Peas Look Like?

  40. …And Now the Test Cross • Mendel then crossed a pure & a hybrid from his F2 generation • This is known as an F2 or test cross • There are two possible test crosses:Homozygous dominant x HybridHomozygous recessive x Hybrid

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

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

  43. F2 Monohybrid SUMMARY • Homozygous x heterozygous(hybrid) • Offspring:50% Homozygous RR or rr50% HeterozygousRr • Phenotypic Ratio is 1:1 • Called Test Cross because the offspring have SAME genotype as parents

  44. Practice Your Crosses Work the P1, F1, and both F2 Crosses for each of the other Seven Pea Plant Traits

  45. Genetic traits in humans can be tracked through family pedigrees • The inheritance of many human traits follows Mendel’s principles and the rules of probability Figure 9.8A

  46. Family pedigrees are used to determine patterns of inheritance and individual genotypes Dd Joshua Lambert Dd Abigail Linnell D_ JohnEddy ? D_ HepzibahDaggett ? D_ Abigail Lambert ? dd JonathanLambert Dd Elizabeth Eddy Dd Dd dd Dd Dd Dd dd Female Male Deaf Hearing Figure 9.8B

  47. Genetic Practice Problems

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