Final answer:
It is true that when both parents are heterozygous for an autosomal recessive trait, 1/4 (25%) of their children are statistically expected to express the trait, according to Mendelian genetics.
Step-by-step explanation:
When both parents are heterozygous for an autosomal recessive trait, it is true that statistically 1/4 of their children will express that trait. This can be reasoned by using simple Mendelian genetics, where two heterozygous parents (each with one dominant and one recessive allele for the trait concerned) can produce offspring with the following combinations: DD, Dd, dD, and dd. The 'dd' combination, which corresponds to the autosomal recessive disorder manifesting, has a 1 in 4 chance of occurring. This indicates that there is a 25% chance that any given child of such a pair will express the recessive trait.
However, it's important to note that while genetics give us probabilities for outcomes across large numbers, actual outcomes in individual families can vary due to chance. Thus, real-world scenarios may not always perfectly follow predicted statistical ratios. For example, a family might have fewer or more than the expected number of children expressing a recessive trait due to random assortment and fertilization events.