Final answer:
Fertilization is the union of a haploid sperm and a haploid egg to form a diploid zygote, maintaining the species' characteristic diploid chromosome number. For an organism with 13 chromosomes per gamete, the correct answer is the first option, illustrating the combination of equal chromosome numbers from each parent.
Step-by-step explanation:
Fertilization is the process in which a haploid sperm cell from the male combines with a haploid egg cell from the female to form a diploid zygote. This crucial reduction of chromosome numbers via meiosis ensures that the resulting offspring maintains the species' characteristic diploid number during sexual reproduction. If we consider an organism in which each gamete contains 13 chromosomes, option 1 is correct: The process in which the sperm (with 13 chromosomes) from the male combines with the egg (with 13 chromosomes) from the female to form the fertilized egg, or zygote, is called fertilization. The zygote will then have 26 chromosomes in total, representing the full diploid set for that species.
Through sexual reproduction, there is a significant potential for genetic variation. This variation originates from the independent assortment of chromosomes during meiosis and the subsequent random fertilization of gametes. Our example organism that has 13 chromosomes per haploid gamete would then exhibit tremendous genetic diversity as a result of these processes.