● Gregor Mendel (1822-1884): An Augustinian friar and scientist, often called the "Father of Modern Genetics."
○ He conducted groundbreaking experiments with garden pea plants (Pisum sativum) in the mid-19th century.
○ He chose pea plants because they were easy to grow, had clearly distinguishable traits (e.g., flower color, seed shape), and could be easily cross-pollinated or self-pollinated.
○ Mendel meticulously kept track of traits through several generations, using quantitative analysis to understand inheritance patterns. His work was revolutionary because it proposed that traits are passed down in discrete units (what we now call genes/alleles), rather than blending.

● Mendel's Key Discoveries (Simplified):
○ Law of Segregation: During gamete formation (meiosis), the two alleles for a heritable trait separate (segregate) from each other, so that each gamete carries only one allele for each gene. When fertilization occurs, the new organism has two alleles for each gene (one from each parent).
○ Law of Independent Assortment: Genes for different traits assort independently of one another during gamete formation, meaning the inheritance of one gene does not affect the inheritance of another (this applies to genes on different chromosomes or far apart on the same chromosome).

● Dominant and Recessive Alleles:
○ Dominant Allele: An allele that, when present, always expresses its associated trait, even if only one copy is inherited. It "masks" the effect of a recessive allele. Represented by a capital letter (e.g., 'T' for tall, 'A' for attached earlobe).
○ Recessive Allele: An allele whose associated trait is only expressed when two copies of the allele are inherited (i.e., in the absence of a dominant allele). Represented by a lowercase letter (e.g., 't' for dwarf, 'a' for free earlobe).

● Homozygous and Heterozygous:
○ Homozygous (Purebred): An individual that has two identical alleles for a specific gene.
■ Homozygous Dominant: Has two dominant alleles (e.g., TT for tall, AA for attached earlobe).
■ Homozygous Recessive: Has two recessive alleles (e.g., tt for dwarf, aa for free earlobe).
○ Heterozygous (Hybrid): An individual that has two different alleles for a specific gene (one dominant and one recessive).
■ Example: Tt for tall (the dominant 'T' allele masks the recessive 't' allele), Aa for attached earlobe.

● Purpose: A Punnett Square is a simple graphical tool used to predict the possible genotypes and phenotypes of offspring resulting from a genetic cross. It illustrates the law of segregation by showing all possible combinations of alleles from the parents' gametes.
● How to Construct a Punnett Square (Monohybrid Cross - one trait):
1. Determine Parental Genotypes: Identify the genotypes of the two parents being crossed.
2. Determine Gametes (Alleles in each egg/sperm): Apply the Law of Segregation – each parent contributes only one allele from each gene pair to their gametes.
■ For a parent with genotype Tt, the gametes will be 1/2 T and 1/2 t.
■ For a parent with genotype TT, the gametes will be all T.
3. Draw the Square: Create a square grid. Place the possible gametes from one parent along the top edge and the possible gametes from the other parent along the left edge.
4. Fill in the Squares: Combine the alleles from the top and side into each inner square. Each inner square represents a possible genotype of an offspring.
5. Interpret the Results:
■ Genotypic Ratio: Count the number of each genotype combination (e.g., TT : Tt : tt).
■ Phenotypic Ratio: Determine the observable traits for each genotype and count the number of each phenotype (e.g., Tall : Dwarf).
■ Express results as ratios or percentages.