The correct answer is option 4 - Gene pool. The gene pool refers to the total collection of all the different genes that exist within a population of a particular species. It represents the genetic diversity present within a population. Each individual within the population carries a specific set of genes, which together make up the gene pool.

Option 1 - Phenotype refers to the observable physical and biochemical traits of an organism, which are determined by both genetic and environmental factors. It does not represent the sum of genes in a population.

Option 2 - Karyotype refers to the number, size, and shape of chromosomes in an organism. It is a visual representation of an individual`s complete set of chromosomes, but it does not represent the sum of genes in a population.

Option 3 - Genotype refers to the specific genetic makeup or combination of alleles of an organism. It represents the genetic information carried by an individual, but it does not represent the sum of genes in a population.

Alert - The correct answer should be option 4 - Gene pool.