Three dominant traits of corn seedlings, tunicate seed (T-), glossy appearance (G-), and liguled stem (L-), are studied along with their recessive counterparts, nontunicate (tt), nonglossy (gg), and liguleless (ll). A trihybrid plant with the three dominant traits is crossed to a nontunicate, nonglossy, liguleless plant. Kernels on ears of progeny plants are scored for the traits, with the following results: Phenotype Number Tunicate, glossy, liguled 102 Tunicate, glossy, liguleless 106 Tunicate, nonglossy, liguled     18 Tunicate, nonglossy, liguleless   20 Nontunicate, glossy, liguled     22 Nontunicate, glossy, liguleless   23 Nontunicate, nonglossy, liguled   99 Nontunicate, nonglossy, liguleless 110 500 If evidence of linkage is present, calculate the recombination frequency or frequencies from the data presented.

Key Concepts

Mendelian Genetics

Mendelian genetics is the study of how traits are inherited through generations based on the principles established by Gregor Mendel. It involves understanding dominant and recessive alleles, where dominant traits mask the expression of recessive ones. This framework is essential for predicting offspring phenotypes from parental genotypes, particularly in dihybrid or trihybrid crosses.

Linkage and Recombination

Linkage refers to the tendency of genes located close to each other on a chromosome to be inherited together during meiosis. Recombination occurs when homologous chromosomes exchange genetic material, leading to new allele combinations. The recombination frequency quantifies this exchange, providing insights into the genetic distance between linked genes, which is crucial for analyzing the results of genetic crosses.

Phenotypic Ratios

Phenotypic ratios represent the relative frequencies of different observable traits in the offspring resulting from a genetic cross. By analyzing the phenotypic outcomes, such as the number of seedlings exhibiting specific traits, one can infer the underlying genotypic ratios and assess whether the observed ratios align with expected Mendelian ratios, indicating potential linkage or independent assortment.