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In a Mendelian cross of red and white varieties of the four O"clock plants, the...

Biology
JAMB 2004

In a Mendelian cross of red and white varieties of the four O"clock plants, the F1 generation expresses incomplete dominance by having flower which are

  • A. white
  • B. red
  • C. pink
  • D. multicoloured
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Correct Answer: Option C
Explanation

In four o'clock plants (Mirabilis jalapa), flower color inheritance is a classic example of incomplete dominance. In this pattern of inheritance, neither allele is completely dominant over the other. When a homozygous red variety (RR) is crossed with a homozygous white variety (rr or WW), the resulting F1 generation is heterozygous (Rr or RW). Because the red pigment is diluted rather than fully expressed or completely masked, the flowers exhibit an intermediate phenotype, which is pink.

A. white: This would only occur if white were the completely dominant trait or if both parents were white.

B. red: This would occur in a standard Mendelian cross where red is completely dominant over white.

D. multicoloured: This phenotype (such as spots or splotches) is characteristic of codominance, where both parental traits are expressed simultaneously and distinctly, rather than blending. 

There is an explanation video available below.


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Explanation Video

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