The correct option is B. Mendelian Inheritance. Explanation of the Correct Answer Mendelian Inheritance refers to the principles of heredity that were first described by Gregor Mendel in the 19th century. Mendel conducted experiments with pea plants and discovered that traits are passed from parents to offspring through discrete units called alleles. Here’s a step-by-step breakdown of why this concept is the correct answer:

1. Definition of Alleles: Alleles are different forms of a gene that can exist at a specific locus (position) on a chromosome. For example, a gene for flower color in pea plants may have a purple allele and a white allele.
2. Principles of Inheritance: Mendel proposed several key principles:
3. Law of Segregation: This law states that during the formation of gametes (sperm and egg), the two alleles for a trait segregate from each other so that each gamete carries only one allele for each gene. For instance, if a plant has one purple allele and one white allele, it will produce gametes that carry either the purple or the white allele, but not both.
4. Law of Independent Assortment: This law states that the alleles for different traits are passed independently of one another from parents to offspring. For example, the inheritance of flower color does not affect the inheritance of seed shape.
5. Genotype and Phenotype: The combination of alleles that an individual has is called its genotype, while the observable traits (like flower color) are referred to as the phenotype. Mendelian inheritance explains how different combinations of alleles can lead to different phenotypes in offspring.
6. Punnett Squares: Mendelian inheritance can be illustrated using Punnett squares, which are diagrams that predict the genotype and phenotype ratios of offspring from a genetic cross. For example, crossing a homozygous purple flower (PP) with a homozygous white flower (pp) would yield all heterozygous purple flowers (Pp) in the first generation.

Explanation of Why Other Options Are Incorrect

• A. Natural Selection: This concept refers to the process by which organisms better adapted to their environment tend to survive and produce more offspring. While natural selection can influence which alleles are passed on over generations, it does not explain the mechanism of how traits are inherited from parents to offspring. Therefore, it is not the correct answer.
• C. Genetic Drift: Genetic drift is a mechanism of evolution that refers to random changes in allele frequencies in a population, especially in small populations. It does not explain the inheritance of traits from parents to offspring but rather how allele frequencies can change over time due to chance events. Thus, it is not relevant to the question.
• D. Gene Flow: Gene flow, or gene migration, is the transfer of alleles or genes from one population to another. While gene flow can introduce new alleles into a population, it does not explain the inheritance of traits from parents to offspring. It is more about the movement of genetic material between populations rather than the mechanism of inheritance.

Summary of Key Points

• Mendelian Inheritance explains how traits are passed from parents to offspring through alleles.
• It includes key principles such as the Law of Segregation and the Law of Independent Assortment.
• The concepts of genotype and phenotype are central to understanding how traits are expressed.
• Other options like Natural Selection, Genetic Drift, and Gene Flow do not directly address the mechanism of inheritance.

This thorough understanding of Mendelian inheritance is crucial for grasping the fundamentals of genetics and how traits are transmitted across generations.