Question

Question 6 You cross a true-breeding red-flowered snapdragon with a true-breeding white-flowered one. All of the FI are pink. What does this say about the alleles for the parental traits? (Concept 14.3) a. Pink is dominant, while red and white are recessive. b. Red is completely dominant. c. Both red and white are pleiotropic. d. Red and white are codominant. e. Red shows incomplete dominance over white.

Answer 1

Answer:

E (Red shows incomplete dominance over white)

Explanation:

This portrays a monohybrid cross involving a single gene coding for flower colour in snapdragon plants. According to the question, a purebreeding red flowered (homozygous) plant is crossed with a purebreeding white flowered (homozygous) plant to produce an all pink flowered offspring. This phenomenon is called INCOMPLETE DOMINANCE.

Mendel, in his experiments, discovered that an allele can mask the expression of another in a heterozygous state. He called the allele that masks DOMINANT allele while the allele that is masked RECESSIVE allele. However, exceptions like INCOMPLETE DOMINANCE, has occurred in the sense that an allele does not completely mask the expression of its allelic pair, instead an intermediate phenotype, which is a combination/blending of both parental phenotypes is produced.

In this case, the red flowered snapdragon (RR) does not completely cover up the expression of white flower (rr), hence a hybrid/heterozygous offspring is produced that combines the phenotypic characteristics of both parents to form an intermediate flower colour (pink). Hence, it can be said that Red flower is incompletely dominant over white flower or no allele/trait is dominant or recessive to another.