When Mendel crossed plants that had always produced only purple flowers with ones that had always produced only white flowers, what was the outcome of the first-generation cross?

It will produce 100% heterozygous purple flowers.

Explanation: First generation cross have homozygous parents. Purple colored flowers are dominant (XX) and the recessive the white colored flowers are (xx). If we cross both parents it will produce four heterozygous purple colored flowers.

All the progeny had a purple flowers in F1 generation.

Explanation:

A plant that always produced purple flower suggest that the plant is homozygous for purple color (PP) and the plant that always produces white flower then it is homozygous for white flower (pp) trait.

So when Mendel crossed these plants he saw that all the offsprings had purple flower which shows that purple is the dominant trait and white is the recessive trait.

P P

p Pp Pp

p Pp Pp

Therefore in first-generation, all the plants produced purple color flowers.