Final answer:
A Punnett square is a diagram that predicts the probability of offspring inheriting genotypes. By placing one parent's alleles on the top and the other's on the side, you can calculate the percentage of each possible genotype. For complex crosses, probability methods are more practical than Punnett squares.
Step-by-step explanation:
Understanding Punnett Squares and Percentages
To tackle percentage calculations using Punnett squares, let's start by reviewing what a Punnett square is. A Punnett square is a tool that predicts the probability of offspring inheriting particular genotypes from their parents. This calculation involves creating a grid where one parent’s alleles (gene versions) are listed across the top and the other parent's alleles down the side. The offspring's possible genotypes are filled in, combining one allele from each parent into the boxes that represent potential offspring.
For instance, if both pea plant parents have purple and white color alleles (Bb), each parent's alleles B and b are placed at the top and side of the square. When you combine the alleles, you get a ratio of their genetic combinations which can be expressed in percentage. If purple is dominant (B) and white is recessive (b), and both parents are heterozygous (Bb), the square would show a 3:1 ratio of purple to white in the offspring. To express this in percentage, 75% of the offspring will be purple, and 25% will be white.
When you're dealing with more complex genetic crosses such as those involving multiple genes, the Punnett square might be less practical. As an alternative, the forked-line and probability methods would be more efficient. In those cases, using the product and sum rules of probability can help determine the expected outcomes.