A homozygous white-flowered plant is crossed with a homozygous dark purple-flowe

Question

A homozygous white-flowered plant is crossed with a homozygous dark purple-flowered plant. All of the seeds grow into pale purple-flowered plants. A) If there is no dosage effect, is it more appropriate to write the genotype for the white-flowered plant “WW” or “pp”? B) What is your reasoning? (3 pts)

Uppercase letters are used to represent dominant genes and lowercase letters are used to represent recessive genes. All of the seeds grew into pale purple-flowered plants, the dominant gene would be purple and the recessive gene would be white. You would write the genotype for the white-flowered plant as “pp” instead of “WW” because the white would be the recessive gene. How would I explain that they are both homozygous? Is this explanation correct?

Purple flower = PP

White flower = pp

P

P

p

Pp

Pp

p

Pp

Pp

P

P

p

Pp

Pp

p

Pp

Pp

Explanation / Answer

As white is recessive and purple is dominant trait, the genotype for white (recessive) should be represented as "pp" but not "WW". Usually dominant trait is represented with capital letter while recessive with lower case. Hence, the provided representation is correct: purple = PP, white = PP.

White is recessive so it would appear only when both the alleles are "pp" (homozygous condition). Also, purple will appear in both heterozygous as well as homozygous conditions. As per the given traits of offsprings, obtained from the cross of white and purple flowered plants, are purple. It indicates that if a parent plant with purple flower would be heterozygous, then white flowered plant might have appeared in offsprings. See the below cross for the case of heterozygous purple flowered plant:

Pp X pp => Pp, Pp, pp, pp.

There are two white and two purple flowered plants.

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