Unit 14 Bio 1201

Chapter 14: Mendelian Genetics

Overview of Mendelian Genetics

  • The "particulate" hypothesis: Parents pass on discrete heritable units known as genes.

Figures and Illustrations

  • Figure 14.1: Introductory Illustration related to Mendelian Genetics.

  • Figure 14.2: Parental generation (P) illustrating the relations between stamens and carpels in the context of first filial generation offspring (F₁).

Mendelian Experimentation

  • ### P Generation Experiment (True-Breeding Parents)

    • First Illustration (Figure 14.3-1):

    • Involved crossing purple flowers (PP) and white flowers (pp).

    • Second Illustration (Figure 14.3-2):

    • Resulted in F₁ generation (hybrids); all offspring exhibited purple flowers, irrespective of the parental phenotype.

    • Third Illustration (Figure 14.3-3):

    • Further self- or cross-pollination of F₁ plants led to F₂ generation.

    • Results: 705 purple-flowered plants and 224 white-flowered plants, confirming dominance.

Table of Mendel’s F₁ Crosses Results

  • Table 14.1 presents Mendel's results for seven characters in pea plants.

    • Dominant vs. Recessive Traits:

    • | Character Trait | Dominant Trait | Recessive Trait | F₂ Generation | Dominant:Recessive Ratio |

    • |----------------------|----------------|------------------|---------------|--------------------------|

    • | Flower color | Purple | White | 705:224 | 3.15:1 |

    • | Flower position | Axial | Terminal | 651:207 | 3.14:1 |

    • | Seed color | Yellow | Green | 6022:2001 | 3.01:1 |

    • | Seed shape | Round | Wrinkled | 5474:1850 | 2.96:1 |

    • | Pod shape | Inflated | Constricted | 882:299 | 2.95:1 |

    • | Pod color | Green | Yellow | 428:152 | 2.82:1 |

    • | Stem length | Tall | Dwarf | 787:277 | 2.84:1 |

Mendel’s Model and the Law of Segregation

  • Mendel's hypothesis explaining the 3:1 inheritance pattern observed in F₂ offspring:

    • Key Concepts (today's terminology):

    1. Alleles: Different versions of genes.

    2. Inheritance: One allele from each parent.

    3. Dominant vs. Recessive: Dominant alleles express their traits over recessive alleles.

    4. Separation: Alleles separate during gamete formation, leading to genetic diversity.

Genetic Makeup and Gametes

  • Genetic Definitions:

    • Figure 14.5-1 depicts P generation with genetic makeup PP (purple) and pp (white).

  • F₁ Generation: All plants are hybrids (Pp).

  • Gametes Representation: P and p contributing to various combinations.

F₂ Generation Outcomes

  • F₂ Ratios:

    • Appearance: 3 purple, 1 white.

    • Genotype Ratios: 1 PP (homozygous), 2 Pp (heterozygous), 1 pp (homozygous). Ratios explained: 3:1 and 1:2:1.

Testcross Predictions

  • Determining the genotype of a purple-flowered parent (unknown: either PP or Pp).

    • If PP: All offspring purple.

    • If Pp: 50% offspring purple, 50% white (Pp x pp).

Di-hybrid Crosses and Independent Assortment

  • Figure 14.8 illustrates the predicted offspring ratios from YYRR and yyrr crossed.

    • Phenotypic Ratio: 3:1.

    • Independent assortment gives a phenotypic ratio of 9:3:3:1.

Probability and Mendelian Inheritance

  • Laws of probability govern Mendelian inheritance:

    • Multiplication Rule: Applies to independent events.

    • Addition Rule: Applies to mutually exclusive events.

Genes in Segregation

  • Figure 14.9: Diagram illustrating segregation of alleles into gametes.

Incomplete Dominance and Codominance

  • Figure 14.10-3: Example showing incomplete dominance in flower color (CWCW x CRCR results in pink gametes through mixing).

ABO Blood Groups

  • Figure 14.11:

    • Three alleles (IA, IB, i) leading to blood group phenotypes.

    • Genotypes leading to blood group appearances: A, B, AB, and O.

Epistasis and Polygenic Inheritance

  • Figure 14.12 deals with the concept of epistasis in genetic interactions.

Polygenic Inheritance

  • Figure 14.13: Distribution of phenotypes according to number of dominant and recessive alleles in skin color variation.

Nature vs. Nurture: Case of Hydrangeas

  • Figure 14.14 presents how hydrangea flower colors can be affected by soil pH (Nature vs. Nurture).

Genetic Disorders and Pedigree Analysis

  • Figure 14.15: Pedigree chart detailing inheritance of traits (e.g., widow’s peak vs no widow’s peak).

    • Determination of dominant or recessive trait based on offspring outcomes.

Genetic Testing Techniques

  • Figure 14.19: Illustrations of amniocentesis and chorionic villus sampling (CVS).

    • Techniques to test fetal genetic conditions before birth.

Conclusion

  • Mendelian genetics underscores the predictable patterns of inheritance observed through controlled experimental cross-breeding, allowing for the establishment of foundational genetics principles which apply to both plant and animal breeding, genetics research, and understanding hereditary diseases.