To solve this problem, we need to compare the genetic content of a somatic cell that has just completed the S phase with that of a gamete of the same species.$\newline \bullet$A somatic cell is a diploid cell, meaning it has two sets of chromosomes (2n).$\newline \bullet$A gamete is a haploid cell, meaning it has one set of chromosomes (n).$\newline \bullet$During the S phase of the cell cycle, DNA replication occurs, doubling the amount of DNA in the cell.$\newline \bullet$After the S phase, a somatic cell still has 2n chromosomes, but the amount of DNA is doubled, resulting in 4C DNA content (where C is the amount of DNA in a haploid set).$\newline \bullet$A gamete, being haploid, has n chromosomes and C DNA content.$\newline$Now, let's compare the somatic cell after the S phase with a gamete:$\newline \bullet$The somatic cell has twice the number of chromosomes (2n vs. n) and four times the amount of DNA (4C vs. C) compared to a gamete.$\newline$Therefore, the correct option is Option 3: Twice the number of chromosomes and four times the amount of DNA.