Answer:
If thick-shelled snails have thick-shelled offspring and thin-shelled snails have thin-shelled offspring then this is good evidence that shell thickness is heritable.
Step-by-step explanation:
Inheritance is a natural mechanism by which genetic information contained in the DNA sequence is passed from parents to offspring. Moreover, heritability is a measure of the genetic influence on the variation in a particular phenotypic trait (e.g., height, eye color, etc.) between individuals in a population. The values of heritability for a particular phenotypic trait range from zero (when all variation in a population comes from environmental factors and therefore is not heritable) to one (when all variation in a population comes from genetic factors and therefore is heritable). For example, in this case, if parental snails always have offspring with the same phenotype for the trait ‘shell thickness’, it would indicate that the heritability for this trait is equal to one, thereby evidencing that all of the variability for the trait 'shell thickness' comes from genetic differences.