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  1. Objectives: General: Understand the concepts underlying Mendelian Genetics. Specific: 1. Identify the factors that influence individuality. 2. Describe the experiment of Mendel and explain their importance to the science of heredity. 3. Solve monohybrid crosses.

  2. What’s up for today? • Background about Gregor Mendel’s life. • Mendel and his experiment. • Characteristics of the garden pea. • Dominant and Recessive Traits • Monohybrid Crosses

  3. What can you say … ?


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

  6. Gregor Johann Mendel • Austrian Monk • Studied at the AgustinianMonastary of St. Thomas in Brno • Studied the inheritance of traits in pea plants • Developed the laws of inheritance • Mendel's work was not recognized until the turn of the 20th century

  7. 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"

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

  9. What did he studied?

  10. Pisumsativum’sCharateristics • Many earlier investigations was done that produced hybrid peas by crossing different varieties. • Large number of true-breeding varieties was available.

  11. Pisumsativum’sCharateristics • Pea plants are small and easy to grow and they have relatively short generation. • Both the male and female sexual organs are enclosed within the pea flower.

  12. 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 fertilization • Self-fertilization can occur in the same flower • Cross-fertilization can occur between flowers

  13. Steps in Mendel’s Experiment • A. Cross-breeding • B. Hybrid-breeding • C. True-breeding

  14. Steps in Mendel’s Experiment • Allowed pea plants of a given variety to produce offspring by self-fertilization for several years. (True-breeding) • Performed crosses between varieties exhibiting alternative forms of characters. (cross-breeding) • Permitted the hybrid offspring to produce by self fertilization for several generations.

  15. Steps in Mendel’s Experiment • True-breeding • Cross-breeding • Hybrid-breeding

  16. 2 ,, 2 B 2

  17. Seven Characters of Pea Plant • Flower color --- Purple (W) or white (w) • Seed Color---- Yellow (G) or  Green (g) • Seed shape--- Round (W) or Wrinkled (w) • Pod Color---  Green (Y) or Yellow (y) • Pod Shape--- Inflated(C) or Constricted (c) • Flower position--- Axial (T) or Terminal (t) • Plant Height--- Tall (D) or Dwarf (d)

  18. Expressed and Unexpressed • Dominant - stronger genes are expressed in the hybrid; represented by a capital letter (R) • Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r)

  19. Expressed and Unexpressed • Homozygous - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr);also called pure  • Heterozygous - gene combination of one dominant & one recessive allele   (e.g. Rr); also called hybrid

  20. Traits • PHENOTYPE is any observable characteristic or trait of an organism: such as its morphology and development. • GENOTYPE isthe genetic makeup of a cell, an organism, or an individual. Represented by letters (WW, YY, Yy, Dd)

  21. Alleles • An alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome.

  22. Steps in Mendel’s Experiment • True-breeding • Cross-breeding • Hybrid-breeding

  23. Test Cross • Used to determine if an individual exhibiting a dominant trait is homozygous or heterozygous for that trait.

  24. Steps in Mendel’s Experiment • True-breeding • Cross-breeding • Hybrid-breeding

  25. Monohybrid Cross • Cross between two individuals having single traits of particular interest. • Monohybrid inheritance is the inheritance of a single characteristic. • Example: • Plant Seed Color (Yellow x Green) • Flower Position (Axial x Terminal)

  26. Generation “Gap” • 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

  27. Punnett Square a diagram that is used to predict an outcome of a particular cross or breeding experiment. Reginald C. Punnett

  28. F1 Generation (Punnett Square) W W F1 Genotype:Ww F1 Phenotype: Purple Ratio:All alike Ww Ww w w Ww Ww Trait: Flower Color W – Purplew – White Cross: Purple Flower x White Flower WW x ww

  29. F2 Generation W w F2 Genotype:_____ F2 Phenotype: _____ Genotype Ratio: ___ Phenotype Ratio: ___ W WW Ww Ww w ww Trait: Flower Color Ww– PurpleWw– Purple Cross: Purple Flower x Purple Flower Ww x Ww

  30. Mendel’s Postulates • UNIT FACTORS IN PAIRS • Genetic characters are controlled “unit factors” that exist in pairs. • DOMINANCE/RECESSIVENESS • When two unlike unit factors is responsible for a single trait, one unit factor is dominant and the other is unexpressed. • SEGREGATION • During gamete formation, the paired unit factors separate or segregate. GENES

  31. Let’s Solve the following • In summer squash, white fruit color (Y) is dominant over yellow fruit color (y).  If a squash plant homozygous for white is crossed with a plant homozygous for yellow, what will the phenotypic and genotypic ratios be for: a. the F1 generation?     b. the F2 generation?


  33. Law of Dominance- States that when pure-breeding plants having contrasting characters are crossed, all the offspring will show only one of the characters. That which appears is the dominant character; that which does not appear is the recessive character.

  34. Principle of Segregation- For any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring.

  35. What is Mendelian Genetics? It describes how genes are transmitted from parent to offspring.

  36. Principle of Independent Assortment- Different pairs of alleles are passed to offspring independently of each other.  The result is that new combinations of genes present in neither parent are possible.  For example, a pea plant's inheritance of the ability to produce purple flowers instead of white ones does not make it more likely that it will also inherit the ability to produce yellow pea seeds in contrast to green ones.