How did Mendel's change scientific knowledge about genetics?

Answer 1

Prior to Mendel, scientists thought that the breeding of two living things, each of the same species but with different characteristics, would result in offspring with a blending of these characteristics. For example, if a giraffe with a long neck mated with one with a short neck; the result would be a giraffe with a medium length neck -- and all subsequent matings with short-necked giraffes would result in progressively shorter necks. Because of this, it was conceptually difficult to imagine how random fluctuations of a characteristic could become dominant within that species.

Mendel showed that characteristics could be passed on from only one of the parents. Thus, a long-necked giraffe could mate with a short-necked giraffe and produce children that had (mostly) long necks. Prior to Mendel, it was unknown how living things passed on specific characteristics. He showed that each parent individually contributes the "knowledge"* of specific characteristics, and that the children might have all, some, or none of each parent's characteristics.

* We now know that this "knowledge" is carried in the genes of the DNA, but Mendel had no idea about this.