The modern synthesis of evolutionary biology integrates Darwinian evolution with Mendelian genetics, emphasizing the inheritance of alleles in diploid organisms, which possess two sets of chromosomes. A fundamental tool in this study is the Punnett square, which allows predictions about the offspring's traits based on parental genotypes.

Key vocabulary includes:

Phenotype: The observable traits of an organism, influenced by genetics and the environment. For example, the coat color of rabbits, such as brown or white, represents their phenotypes.
Gene: A segment of DNA that encodes for a specific trait or protein. In the rabbit example, the gene responsible for coat color is of particular interest.
Allele: Different versions of a gene. For the coat color gene, there are two alleles: dominant (represented as A) and recessive (represented as a).
Genotype: The specific combination of alleles an organism possesses. For instance, a brown rabbit with the genotype aa is homozygous recessive, while a white rabbit could be either homozygous dominant (AA) or heterozygous (Aa).

While Mendelian genetics focuses on single matings, population genetics expands this view to consider allele inheritance across entire populations. This approach introduces the concept of the gene pool, which encompasses all alleles present in a population, regardless of the organisms they belong to. For example, if we analyze a population of rabbits, the gene pool would include all alleles from both brown and white rabbits.

From the gene pool, we can derive allele frequency, which is the proportion of a specific allele within the gene pool. For instance, if 60% of the alleles are dominant (A) and 40% are recessive (a), these percentages represent the allele frequencies. Changes in allele frequency over time are indicative of evolution, highlighting the importance of understanding the gene pool and its dynamics in the context of modern biology.

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