Question

A plant with red flowers is crossed with a plant with white flowers and the plant does not show incomplete dominance or codominance. Predict diagrammatically the above and add a note on type of cross.

Answer 1

Hint: Incomplete dominance is a condition where a blending of characters is seen in a heterozygotic individual. Co-dominance is a condition where there is no dominant and recessive relationship between the alleles and both the alleles express its phenotype.

Complete answer:
Let the alleles coding for the red flowers be $RR$ (homozygous dominant) and the alleles coding for the white flowers be $rr$ (homozygous recessive).
According to the question red flower is crossed with a white flower,
Parental generation $(P)$ -> $RR$ x $rr$
Gametes -> $R,R$ and $r,r$
$F1$generation -> $Rr$
The genotype $Rr$ represents a $F1$ hybrid which is again red in colour.
On selfing of $F1$, that is -> $Rr$ x $Rr$

$F2$ generation:

Gametes	$R$	$r$
$R$	$RR$	$Rr$
$r$	$Rr$	$rr$

Table: Selfing of $F1$ showing the genotypes of $F2$ generation.
The genotypic ratio in the $F2$ generation is $RR$:$Rr$:$rr$= $1:2:1$
The phenotypic ratio in the $F2$ generation is Red: white = $3:1$

This is a simple Mendelian monohybrid cross. We can confirm this by the ratio mentioned above. As we can see, the red phenotype is dominant over the white phenotype. That is the reason red colour is shown in the hybrid. It is referred to as a monohybrid cross because we are only considering one phenotype for the cross that is the colour of the flower.

Note: Both codominance and incomplete dominance are types of inheritance that deviates from Mendelian inheritance. Since it is mentioned that it does not show incomplete dominance there will be no appearance of an intermediate pink colour in the $F1$ hybrid. If there was co-dominance then there would have been an appearance of both red and white colours in the $F1$ generation.