beckygardener said:You wrote, "If I cross 'White Temptation' with 'Gentle Shepherd' and all the seedlings are white-flowered like their parents then white flower is recessive."
Why would it be recessive? I would have expected the white trait to be dominant since both parents were white flowered.
It is not usually possible to definitively classify a characteristic as dominant/recessive/additive/etc. from the observations of only one cross. So one must examine the results of several different kinds of crosses to determine how a characteristic might be inherited.
In the case of red flowers and white flowers in my example first a red flowered plant was crossed with a white flowered plant and all the seedlings were red coloured. Only one parent needed to be red and even though the other parent was white all the seedlings were red flowered. Two of those red flowered seedlings were crossed together and some of their seedlings were red flowered and some were white flowered. Finally two white flowered plants were crossed with each other and all their seedlings were white flowered. Both parents had to be white flowered for all their seedlings to be white flowered. One needs to look at the results of all three of the different types of crosses to determine how red and white flowers are inherited.
More of the example. If I only cross 'Pardon Me' with another red flowered plant (I make no other crosses) and all the seedlings are red-flowered I cannot tell whether red flowers is a dominant characteristic or a recessive characteristic. If I only cross 'White Temptation' with 'Gentle Shepherd' and all the seedlings are
white flowered I cannot tell whether white flowers is a dominant characteristic or a recessive characteristic. I have to make crosses between red flowered plants and white flowered plants and usually I also have to make crosses with the seedlings so produced to get a good idea about how those two flower colours are inherited.
In fact, the classical test for determining how characteristics are inherited is to cross two individuals to produce the F1 seedlings. Then to cross two of those F1 seedlings with each other to produce the F2 seedlings (or usually to self-pollinate one of the F1 seedlings) and to cross one of those F1 seedlings back to one parent and another of those F1 seedlings back to the other parent. Finally, if one wants to complete the analysis one would take some of the F2 seedlings showing the different parental characteristics and self-pollinate them.
Even in the simplest Mendelian case I could have the following types of crosses (red flower is dominant to white flower, white flower is recessive to red flower):
red flowered x red flowered producing all red flowered seedlings
red flowered x red flowered producing red flowered and white flowered seedlings
red flowered x white flowered producing all red flowered seedlings
red flowered x white flowered producing some red flowered and white flowered seedlings
white flowered x white flowered producing all white flowered
