Mendelian Genetics

Differentiate between blending inheritance and Mendelian inheritance.
Explain why Mendel’s experiments were successful.
Differentiate between the following terms: genotype vs phenotype, gene vs allele, homozygous vs heterozygous, and dominant vs recessive.
Explain Mendel’s law of segregation and law of independent assortment.
Use a Punnett square to calculate the expected proportions of genotypes and phenotypes in the offspring of monohybrid and dihybrid crosses.
Relate genetics (alleles and genes) to cellular structures (chromosomes and DNA).

Results in Clonal Offspring:
- New shoots sprout from underground stems, producing a genetically identical clone of trees.
Confers a Large Numerical Advantage:
- Asexual reproduction can lead to rapid population increase as all offspring are genetically identical.
- Generational Comparison:
- Generation 1 → Generation 2 → Generation 3
  - Results in densely populated clonal growth in contrast to sexual reproduction, which introduces genetic diversity.

Theories included:
- Inheritance of Acquired Characteristics: Characteristics acquired during an organism’s lifetime were believed to be passed on to the next generation.
- Chromosome Theory of Inheritance: Proposed that genes are located on chromosomes, and patterns of inheritance are determined by chromosome behavior during meiosis.
- Blending Inheritance: Suggested that offspring's traits are a blend of parental traits, leading to phenotypic convergence which does not account for trait reemergence in later generations.

Study of Inheritance in Garden Peas:
- Utilized scientific methods to explore inheritance.
- Demonstrated that characteristics can be transferred from generation to generation as discrete “particles” (genes).
- Each parent has two copies of each gene, passing on a single copy to offspring.
- Variation of traits is preserved.
Advantages of Studying Inheritance in Garden Peas:
1. Strict Control Over Mating:
- Self-fertilization: Male parts of one plant pollinate and fertilize female parts of the same plant.
- Cross-fertilization: Male parts of one plant pollinate and fertilize female parts of a different plant.
1. Easily Distinguishable Traits:
- Traits like purple or white flowers can be readily observed and documented.
1. Ease of Cultivation:
- Garden peas are simple to grow, allowing extensive experimentation.
Mendel’s Experimental Approach:
- Selected seven traits with two distinct forms (e.g., color, shape).
- Developed true-breeding lines, which self-fertilize to produce offspring identical to the parent plants.
- Created hybrids by crossing true-breeding plants with contrasting traits.
- Maintained meticulous records and statistical analyses of his results across multiple generations.

Wild Type: Traits most commonly found in nature.
Cross: Cross-fertilization of two different plants.
Generations:
- P Generation: Parental plants.
- F1 Generation: Hybrid offspring of parental plants.
- F2 Generation: Offspring of F1 plants that self-fertilize or cross-fertilize with each other.
Punnett Square: A device used to predict the results of a genetic cross.

Genotype: The genetic make-up of an organism.
Phenotype: An organism’s expressed physical traits, usually determined by somatic cells.

Alleles: Alternate forms of a gene.
- Dominant Allele: The allele that determines the phenotype and is expressed even when paired with a recessive allele.
- Recessive Allele: An alternative to the dominant allele, which is expressed only when paired with another recessive allele.

Gene Locus: The specific location of a gene on a homologous chromosome.
Genotypes:
- Homozygous: Identical alleles (e.g., PP or aa).
- Heterozygous: Different alleles (e.g., Yy).

Traits and Phenotypes:
- Seed Shape: Round, Wrinkled.
- Parental (P) Generation: Round x Round, Wrinkled x Wrinkled.
- Filial 1 (F₁) Generation Results: All offspring display the dominant phenotype (Round).

Monohybrid Cross Results:
- F1 Progeny: All Round (dominant).
- F2 Progeny: Resulting ratio of phenotypes is 3 Round: 1 Wrinkled, demonstrating that the wrinkled trait reemerges.
Mendel’s Hypothesis:
- Heritable characteristics controlled by discrete units (genes).
- Each individual inherits two genes for a trait, one from each parent.
- Alleles segregate during gamete formation (Mendel's 1st Law): Each gamete receives one of the parent's two alleles for each gene.

Monohybrid Cross Methodology:
- Example: Crossing two heterozygous parents (Tt):
- Write down the genotypes of both parents, list possible gametes (T or t), and fill in a Punnett square to visualize outcomes.
- F2 Generation: The resulting offspring ratios in genotypes (1:2:1) and phenotypes (3:1).

Mendel’s 1st Law: Different alleles of a gene segregate during gamete formation.
Mendel’s 2nd Law: Alleles of different genes assort independently.
Chromosome Theory of Inheritance: Genes are located on chromosomes; inheritance patterns are determined by chromosome behavior during meiosis.

Observed Ratios in F2 Generation Examples:
- Stem length: Tall (787) to Short (277) = 2.84:1.
- Pod shape: Inflated (882) to Constricted (299) = 2.95:1.
- Seed shape: Round (5474) to Wrinkled (1850) = 2.96:1.
- Seed color: Yellow (6022) to Green (2001) = 3.01:1.
- Counts provide evidence supporting Mendelian ratios, confirming his laws of inheritance.

Familiarize with genetics terminology: gene, allele, dominant, recessive, homozygous, heterozygous, P, F1, F2, true-breeding, hybrid.
Practice creating possible gametes from given genotypes.
Perform basic one trait and two trait genetic crosses.
Understand the relationship between Mendel’s Laws and cellular processes during meiosis.