![]() ![]() The specific combination of alleles that comprise the genotype determines which phenotype is observed. There were nine different genotypes in the F2 plants resulting from the dihybrid cross. The phenotypic ratio in the F2 plants was 9:3:3:1. The F2 generation pea plants expressed either round or wrinkled seed shape with either yellow or green seed color. Self-pollination in the F1 plants resulted in a different phenotypic ratio in the F2 plants. The phenotypes (observable physical traits) in the F1 plants were the dominant traits of round seed shape and yellow seed color. Genotype determines which traits are expressed in the phenotype. ![]() In Mendel's experiment with seed shape and color, the genotype of the F1 plants was RrYy. Inherited allele combinations determine an organisms genotype (gene composition) and phenotype (expressed traits). They are separated during meiosis (process for the production of sex cells) and united at random during fertilization.ĭiploid organisms inherit two alleles per trait, one from each parent. These different forms are called alleles, which are positioned at specific locations on specific chromosomes.Īlleles are transmitted from parents to offspring by sexual reproduction. Each gene is located on a chromosome and can exist in more than one form. Genes are segments of DNA that determine distinct traits. Wikimedia Commons/CC BY-SA 3.0 How Genes and Alleles Determine Traits This means that the dominant traits of round seed shape and yellow color completely masked the recessive traits in the F1 generation. The resulting offspring (or F1 generation) were all heterozygous for round seed shape and yellow seeds (RrYy). Wrinkled seed shape (rr) and green seed color (yy) are recessive. In this cross, the traits for round seed shape (RR) and yellow seed color (YY) are dominant. For example, a plant that had round seeds and yellow seed color was cross-pollinated with a plant that had wrinkled seeds and green seed color. Mendel performed dihybrid crosses in plants that were true-breeding for two traits. Mendel's Independent Assortment Experiment
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