Final answer:
The probability that the offspring will show the dominant phenotype when two heterozygous organisms are crossed is 75%, following Mendelian genetics principles.
Step-by-step explanation:
When you cross two heterozygous organisms, the probability that the offspring will show the dominant phenotype is 75%. This is determined by using a Punnett square to show the possible combinations of alleles that can occur from such a cross.
If we have two heterozygotes, Bb, we can pair each allele from one parent with each allele from the other parent to determine the genotypes of the offspring. If B represents the dominant allele and b the recessive allele, the resulting genotypes can be BB, Bb, Bb, and bb. Among these, BB and Bb both exhibit the dominant phenotype. Thus, we have three out of four, or 75%, of the offspring displaying the dominant phenotype, according to the laws of probability and Mendelian genetics.
Explaining these crosses to friends can help make the concept clearer. In a group of offspring from two heterozygous parents, expect three to show the dominant trait for every one that shows the recessive trait. This follows the 3:1 ratio, which reflects the fact that the dominant phenotype appears whenever at least one dominant allele is present.