Mendel’s laws, monohybrid and dihybrid crosses

1. Introduction

1. Genetics is the branch of biology that studies heredity and variation.
2. Heredity refers to the transmission of traits from parents to offspring.
3. Variation is the difference in traits among individuals of a species.
4. Gregor Mendel, known as the "Father of Genetics," conducted experiments on pea plants to understand inheritance.

2. Mendel’s Laws of Inheritance

1. Law of Dominance: In a heterozygous condition, the dominant allele is expressed, while the recessive allele remains hidden.
2. Law of Segregation: During gamete formation, the two alleles for a trait separate, and each gamete receives only one allele.
3. Law of Independent Assortment: The inheritance of one trait is independent of another, provided they are on different chromosomes.

3. Monohybrid Cross

1. A monohybrid cross is a genetic cross involving a single trait.
2. Mendel studied height in pea plants by crossing a tall plant (TT) with a dwarf plant (tt).
3. The F1 generation (Tt) showed only tall plants, proving the dominance of the "T" allele.
4. The F2 generation showed a 3:1 phenotypic ratio (3 tall: 1 dwarf).

4. Dihybrid Cross

1. A dihybrid cross involves two traits.
2. Mendel studied seed color (yellow/green) and seed shape (round/wrinkled).
3. Crossing pure yellow-round (YYRR) with green-wrinkled (yyrr) gave F1 hybrids (YyRr), all showing dominant traits.
4. The F2 generation showed a 9:3:3:1 phenotypic ratio.

5. Mendelian vs. Non-Mendelian Inheritance

1. Mendelian inheritance follows dominant-recessive patterns.
2. Non-Mendelian inheritance includes incomplete dominance, codominance, and multiple alleles.

6. Significance of Mendel’s Work

1. Helped establish the foundation of modern genetics.
2. Explained inheritance patterns through laws.
3. Later discoveries, such as DNA and chromosomes, supported his theories.