Question

A self-pollinating plant with orange flowers and alternating leaf arrangement produces
Plants with red flowers and alternating leave- 47
Plants with orange flowers and alternating leaves- 103
Plants with yellow flowers and alternating leaves- 51
If a yellow-flowered offspring were self-pollinated, what would the resulting plant's flowers look like?
A. 100% yellow
B. 100% red
C. 100% orange
D. 50% yellow, 50% red

Answer 1

Plant having orange phenotype generated plants with yellow and red flowers. That means the gene expressing colour of a flower had two alleles i.e., yellow and red. The heterozygous allele gave a different combination of colour of the flower which was orange, which can be a mixture of two basic colours expressed by dominant and recessive alleles.

Step by step answer: The ‘Y’ allele is dominant and expresses yellow flowers whereas the ‘y’ allele is recessive and expresses red flowers. But here as orange flowers are also generated it can be concluded that the yellow allele is incompletely dominant over the red allele and thus ‘Yy’ heterozygous allele gives orange coloured flower. Incomplete dominance is a phenomenon in which the dominant allele is not entirely masking the expression of the recessive allele and as a result the heterozygous off-springs partially express both the allele as a combined phenotype. Yellow coloured flowers are only generated when homozygous dominant alleles are expressed and red coloured flowers are only generated when homozygous recessive alleles are expressed. So, if yellow-flowered (YY) offspring were self-pollinated the next generation will only have yellow coloured plants having genotype YY.
Hence, the correct answer is option A. 100% yellow
Additional information: Such inheritance does not follow Mendel’s rule of segregation.

Note: Incomplete dominance is different from codominance. Because in codominance neither of the alleles is suppressed but both dominant and recessive alleles are expressed simultaneously in the off-spring. Therefore, whenever the dominant and recessive allele gives rise to a third expression which is completely different from both the alleles it is the incomplete dominant inheritance.