Gregor Mendel bred a population of pea plants, producing a large number of offspring. Of this offspring, 6,022 plants produced yellow seeds and 2,001 produced green seeds. What percentage of the total offspring displayed the dominant trait? Give your answer to the nearest whole number.
Gregor Mendel, known as the father of modern genetics, was an Austrian monk and scientist. He spent seven years breeding pea plants in order to study how they inherit certain features. So let’s begin by reviewing some of the key ideas associated with inheritance.
All organisms from single-celled paramecium to complex multicellular humans have features that are inherited or passed down genetically from parent to offspring. We call these features characteristics. A trait is a variation of a characteristic. For example, in humans, the shape of our hairline is a characteristic, and a straight or V-shaped hairline, often called a widow’s peak, are traits.
In our question, seed color is the characteristic, and yellow seeds or green seeds are traits. You may remember that the expression of traits is determined by the combination of alleles or alternate gene versions that an organism inherits. In humans, hairline shape is determined by the combination of two alleles represented by uppercase W and lowercase w. Similarly, seed color is also determined by the combination of two alleles represented by uppercase Y and lowercase y. We refer to the combination of an organism’s alleles as its genotype. And genotype determines phenotype, which is the set of observable traits of an organism.
Now let’s return to our question. We are asked to find the percentage of pea offspring displaying the dominant trait. The dominant trait will be expressed when at least one copy of the dominant allele is inherited. We have already determined that the two traits are yellow seeds and green seeds. But we need to figure out which of these traits is the dominant trait.
There are 6,022 plants that produced yellow seeds and 2,001 plants that produced green seeds. The number of plants producing yellow seeds is much greater than the number of plants producing green seeds. We know that in a cross of a heterozygous mendelian trait, we will see more offspring with the dominant phenotype or trait than the recessive phenotype. So we can conclude that yellow seeds is the dominant trait.
Our next step is to find the total number of offspring by adding the plants that displayed yellow seeds and the plants that displayed green seeds. The total number of offspring is 8,023. Finally, we need to find the percentage of this total that displayed yellow seeds. We do this by dividing the number of offspring that produced yellow seeds by the total number of offspring and multiplying by 100 percent, remembering to round to the nearest whole number. So the percentage of offspring displaying the dominant trait of yellow seeds is 75 percent.