Final answer:
Height in pea plants is genetically controlled by two alleles, with tallness (T) being dominant over shortness (t). A test cross can suggest an unknown genotype, but larger samples are needed for accuracy. Observed phenotypic ratios can confirm or challenge Mendelian predictions.
Step-by-step explanation:
The height of pea plants is indeed genetically controlled, which is explained by Mendelian genetics. Within pea plants, the height gene consists of two alleles: a dominant allele for tallness (T) and a recessive allele for shortness (t). According to Mendel's experiments, these alleles determine the phenotype of the plant with the tall allele being dominant over the short allele.
When conducting a test cross involving pea plants, if one parent has a known genotype of wrinkled peas (rr) and is crossed with a plant of unknown genotype with round peas, the phenotype of the offspring can suggest the genotype of the unknown parent. For instance, if all offspring display round peas, the unknown parent could potentially be homozygous dominant (RR) or heterozygous (Rr). However, to determine this with certainty, a larger sample size would be necessary, since a sample of three could coincidentally all show the dominant phenotype even if the unknown parent was heterozygous.
To analyze data in a way consistent with Mendelian laws, look for phenotypic ratios that approximate those predicted by Mendel. If the observed ratio significantly deviates from the expected ratio, this suggests additional genetic complexities that Mendel's simple dominant-recessive model does not explain.