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Mendelian Genetics

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Mendelian Genetics

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    1. Mendelian Genetics

    2. Mendel’s Genetics Experiments with Peas

    3. Pea Characters Investigated

    4. Genetic Loci & Alleles

    5. Genetic Recombination at Fertilization

    6. Mendel’s Test for Evaluating the Inheritance of Seed Shape in Pea Plants Recognized two different traits for the seed shape character in pea plants: round versus wrinkled seeds. Established true-breeding varieties for each of these traits.

    7. Mendel’s Test for Evaluating the Inheritance of Seed Shape in Pea Plants Crossed true-breeding round seed variety with the true breeding wrinkled seed variety (this represents the Parental, or P, cross). Offspring (F1 generation) are called “hybrids”.

    8. 100% of these hybrids produced round seeds. Crossed these F1 generation hybrids among each other (individual crosses being selected at random). Mendel’s Test for Evaluating the Inheritance of Seed Shape in Pea Plants

    9. Results for their offspring (F2 generation): 5474 (74.7%) were plants that produced round seeds. Mendel’s Test for Evaluating the Inheritance of Seed Shape in Pea Plants

    10. Results for their offspring (F2 generation): 1850 (25.3%) were plants that produced wrinkled seeds. Mendel’s Test for Evaluating the Inheritance of Seed Shape in Pea Plants

    11. Results for their offspring (F2 generation): Ratio of round:wrinkled = approx. 3:1 Mendel’s Test for Evaluating the Inheritance of Seed Shape in Pea Plants

    12. Mendel’s Explanation for his Results For every character (e.g., seed shape) an individual possess two instruction sets (alleles). One of these alleles was originally derived from the individual’s mother, the other allele being originally derived from the individual’s father.

    13. Mendel’s Explanation for his Results In true-breeding individuals, both alleles are the same. Hybrids, on the other hand, have one of each kind of allele.

    14. Mendel’s Explanation for his Results Mendel believed that only two alleles were possible for a given genetic character, and that one of the alleles (the dominant one) masked the expression of the other (the recessive one) in the hybrid.

    15. Mendel’s Explanation for his Results When the hybrid formed gametes, only one of the two possible alleles would end up in a gamete. However, both alleles possessed an equal chance of appearing in a gamete.

    16. Mendel’s Explanation for his Results Defining alleles: R = the round allele (dominant). r = the wrinkled allele (recessive).

    17. Mendel’s Explanation for his Results Defining genotypes & their phenotypes: RR genotype (homozygous dominant) = round phenotype. rr genotype (homozygous recessive) = wrinkled phenotype. Rr genotype (heterozygous) = round phenotype

    18. Pea Shapes

    19. Mendel’s Explanation for his Results Parental (P) Cross Round X Wrinkled RR rr Gametes: R r

    20. Mendel’s Explanation for his Results F1 Generation Hybrids 100% Round 100% Rr

    21. Mendel’s Explanation for his Results F1 Generation Cross Round X Round Rr Rr Gametes: R r R r

    22. Mendel’s Explanation for his Results F1 Gametes: R r R r F2 Generation Outcome Round Wrinkled RR Rr Rr rr Note: 3:1 ratio of round:wrinkled

    23. Punnett Square Diagram

    24. Mendel’s Law of Segregation

    25. A Testcross

    26. Punnett Square Diagram for Testcross

    27. Mendel’s Law of Independent Assortment

    28. Mendel’s Test Using the Seed Shape Character with the Seed Color Character Define Alleles and Associated Traits: Seed Shape Character R = round seed trait (dominant) r = wrinkle seed trait (recessive)

    29. Mendel’s Test Using the Seed Shape Character with the Seed Color Character Define Alleles and Associated Traits: Seed Color Character Y = yellow seed trait (dominant) y = green seed trait (recessive)

    30. Mendel’s Test Using the Seed Shape Character with the Seed Color Character Parental (P) cross: crossed true-breeding plants that produce round-yellow (RRYY) seeds with true-breeding plants that produce wrinkled-green seeds (rryy).

    31. Mendel’s Test Using the Seed Shape Character with the Seed Color Character F1 Generation: hybrids for both characters (Rr & Yy; or RrYy) were100% round-yellow. F1 Generation Individuals (RrYy) crossed among each other.

    32. Mendel’s Test Using the Seed Shape Character with the Seed Color Character F2 Generation Results: 315 (56.7%) round-yellow 108 (19.4%) round-green 101 (18.2%) wrinkled-yellow 32 (5.8%) wrinkled-green

    33. No Independent Assortment

    34. With Independent Assortment

    35. Calculating Expected Frequencies Expect 9/16 of the F2 generation offspring to be round-yellow. Therefore, of a total of 556 offspring the expected number (frequency) of round-yellow offspring may be calculated as follows:

    36. Calculating Expected Frequencies Expect 3/16 of the F2 generation offspring to be round-green. Therefore, of a total of 556 offspring the expected number (frequency) of round-yellow offspring may be calculated as follows:

    37. Calculating Expected Frequencies Expect 3/16 of the F2 generation offspring to be wrinkled-yellow. Therefore, of a total of 556 offspring the expected number (frequency) of round-yellow offspring may be calculated as follows:

    38. Calculating Expected Frequencies Expect 1/16 of the F2 generation offspring to be wrinkled-yellow. Therefore, of a total of 556 offspring the expected number (frequency) of round-yellow offspring may be calculated as follows:

    39. Comparing Observed to Expected Results Observed Round-Yellow 315 Round-Green 108 Wrinkled-Yellow 101 Wrinkled-Green 32 Expected Round-Yellow 312.75 Round-Green 104.25 Wrinkled-Yellow 104.25 Wrinkled-Green 34.75

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