In a given hybridization between two flowers, red "r" is dominant, and white "r" is recessive. in a cross between two white-flowered plants, all of the offspring had white flowers. if a plant grower wanted to produce red flowers, what should s/he consider during breeding?

Ans.

The dominant allele can be defined as the allele, which can express itself in both heterozygous and homozygous conditions. On the other hand, recessive allele can only express itself in homozygous condition (when both the alleles for recessive traits are present. It means presence of one dominant allele can hide the expression of recessive allele.

In given experimental flower, red color is dominant over white color of flower. So, 'if a plant grower wants to produce red flowers only, he should choose both the parent plants having red flowers as they have at least one allele for red color that would transfer to their offspring.'

Lets understand this in a calculative way,  

Let the parents genotype be RR and Rr

The offspring’s produced are – RR, Rr, Rr, RR, Thus all the offsprings are white as r is recessive, for producing a red flower the offspring must have “rr” genotype.  

Now if parents have Rr and rr genotype , then the offspring would have Rr, rr, rr, Rr giving two white and two red flower. Of the second case may be where both the parent white flower are the carrier with genotype “Rr”

Thus in order to produce red flower the parents with following genotypes is necessary –  

a)Both parents having Rr

b)One parents with rr and the other parent with Rr genotype

they are known to reach a speed of 21 miles per hour

i think the answer would be d