When marijuana seeds are classified as regular it means that the seeds when germinated can produce either male or female plants. It is expected that a batch of regular seeds can have about 50% male and 50% female so the tendency to have male together with female plants is about even. However, the sex of marijuana plants cannot be determined with certainty until they start to flower.
When the flowering stage starts, the male marijuana plants will start to pollinate the female plants and this will lead to producing seeds instead of the desired buds.
Most marijuana growers do not want the female plants to be fertilized so they immediately take out the male plants once their sex is identified during the initial stage of flowering. If the female marijuana plants are not fertilized there will be no seeds in the buds and the THC potency is higher.