Final answer:
The parent pea plant is likely heterozygous (Tt) resulting in a 3:1 phenotypic ratio of tall to short progeny. When these tall progeny self-fertilize, approximately 25% are expected to be homozygous dominant (TT) and will breed true, yielding about 18 tall plants that will only produce tall offspring.
Step-by-step explanation:
The phenotypic outcome in pea plants is based on Mendelian genetics principles, where dominant alleles mask the effect of recessive alleles. A pea plant that is homozygous dominant (TT) for the tall trait will be tall, just as a heterozygous pea plant (Tt) will also be tall, indicating that two different genotypes can lead to the same phenotype. The progeny consisting of 72 tall plants and 19 short plants from a self-fertilized tall pea plant suggest that the parent plant was heterozygous (Tt). When the tall progeny undergo self-fertilization, we can expect a 3:1 ratio of tall to short plants, assuming the tall plants are also all heterozygous.
According to the Punnett square analysis, crossing two heterozygous tall pea plants (Tt x Tt) would give a genotypic ratio of 1:2:1, which is 1 TT (homozygous dominant), 2 Tt (heterozygous), and 1 tt (homozygous recessive). This implies we can expect 1/4, or 25%, of the tall plants to be homozygous dominant (TT) and breed true with tall offspring only. With 72 tall plants as the starting point, approximately 18 tall plants would be expected to breed true, which means they will produce only tall progeny when self-fertilized.