Final answer:
In the cross between two heterozygous pea plants, you would expect 75% of the offspring to be yellow, as yellow is the dominant color. This translates to approximately 555 yellow peas out of 740 offspring, confirming Mendel's hypothesis about trait segregation and random combination.
Step-by-step explanation:
When crossing heterozygous pea plants (CᵢCᵢ x CᵢCᵢ), where yellow peas are dominant over green, you would expect a phenotypic ratio of three yellow to one green based on Mendelian genetics. Each heterozygous plant has a genotype of Yy, which means they can produce two types of gametes: Y and y. When these gametes combine during fertilization, they can form YY (homozygous dominant), Yy (heterozygous), or yy (homozygous recessive) pea plants. Since yellow is dominant, both YY and Yy plants will have a yellow phenotype. The Punnett square predicts that 25% of offspring will be YY, 50% will be Yy, and 25% will be yy. Therefore, 75% are expected to be yellow.
To determine the expected number of yellow peas amongst 740 offspring, we calculate 75% of 740, which gives us 555. This matches the observation that 555 of the peas are yellow, which supports Mendel's hypothesis that traits, such as pea color, segregate and assort independently during meiosis and combine randomly during fertilization. Mendel's experiments with pea plants formed the foundation of classical genetics, leading to the discovery of the law of segregation and the law of independent assortment.
Each offspring's phenotype is a result of its genotype, where yellow is dominant over green (Y > y). Therefore, any genotype that includes at least one dominant 'Y' allele will express the yellow phenotype. However, Mendel's experiments went beyond just predicting phenotypes; he developed the test cross to distinguish between homozygous dominant (YY) and heterozygous (Yy) organisms. This is a crucial element of Mendelian genetics, as it provides a tool for identifying the genetic makeup behind a dominant trait.