If a heterozygous plant self-fertilizes, the possible results are that the offspring will be either homozygous dominant (TT), heterozygous (Tt), or homozygous recessive (tt).
The genotypic ratio for the offspring of a heterozygous plant that self-fertilizes is 1:2:1, meaning that there is a 1 in 4 (25%) chance that the offspring will be homozygous dominant (TT), a 2 in 4 (50%) chance that the offspring will be heterozygous (Tt), and a 1 in 4 (25%) chance that the offspring will be homozygous recessive (tt).
The phenotypic ratio for the offspring of a heterozygous plant that self-fertilizes is 3:1, meaning that there is a 3 in 4 (75%) chance that the offspring will have the dominant trait (tallness) and a 1 in 4 (25%) chance that the offspring will have the recessive trait (shortness).
The probability of having a homozygous tall plant is 1 in 4 (25%) if a heterozygous plant self-fertilizes.
Even when a plant self-fertilizes, there is still genetic variation between the offspring and the parent. This is because self-fertilization only involves the mixing of the genes that are present in the parent plant, and it does not create new genetic variation. Therefore, the offspring of a plant that self-fertilizes will have the same genetic variation as the parent plant, but the specific combination of genes in each individual offspring may be different from the parent.