In pigs, coat color may be sandy, red, or white. A geneticist spent several years mating true-breeding pigs of all different color combinations, even obtaining true-breeding lines from different parts of the country. For crosses 1 and 4 in the following table, she encountered a major problem: her computer crashed and she lost the data. She nevertheless persevered and, using the limited data shown here, was able to predict the mode of inheritance and the number of genes involved, as well as to assign genotypes to each coat color. Attempt to duplicate her analysis, based on the available data generated from the crosses shown.
When you have formulated a hypothesis to explain the mode of inheritance and assigned genotypes to the respective coat colors, predict the outcomes of the generations where the data were lost.

Verified step by step guidance

1. Step 1: Carefully examine the available data from the crosses provided in the table, focusing on the phenotypes (sandy, red, white) and their corresponding offspring ratios. Identify which crosses have complete data and which are missing (crosses 1 and 4).
2. Step 2: Formulate hypotheses about the mode of inheritance by considering common genetic patterns such as dominance, recessiveness, incomplete dominance, or epistasis. Since there are three phenotypes, consider whether one or two genes might be involved and how their alleles could interact to produce these colors.
3. Step 3: Assign tentative genotypes to each coat color based on the observed phenotypic ratios in the crosses with complete data. For example, if sandy is dominant over red and white, or if two genes interact to produce the colors, write down possible allele combinations (e.g., AAbb, aaBB, AaBb) that could explain the phenotypes.
4. Step 4: Use the genotypes assigned to the parental pigs in the known crosses to predict the expected genotypic and phenotypic ratios in their offspring. Check if these predictions match the observed data to validate your hypothesis about the mode of inheritance and number of genes involved.
5. Step 5: Apply your validated genetic model to predict the outcomes (genotypic and phenotypic ratios) of the crosses 1 and 4 where data were lost. Use Punnett squares or probability calculations based on the assigned genotypes to determine the expected distribution of coat colors in the offspring.

Key Concepts

Modes of Inheritance

Modes of inheritance describe how traits are transmitted from parents to offspring, including dominant, recessive, codominant, and polygenic patterns. Understanding these patterns helps predict offspring phenotypes based on parental genotypes, which is essential when analyzing coat color inheritance in pigs.

True-Breeding Lines and Genotype Assignment

True-breeding lines are populations that consistently produce offspring with the same phenotype, indicating homozygosity for the trait. Identifying true-breeding lines allows geneticists to assign genotypes to phenotypes, which is critical for deducing the genetic basis of traits like coat color.

Predicting Genetic Cross Outcomes

Predicting outcomes of genetic crosses involves using known genotypes and inheritance patterns to forecast offspring phenotypes and genotypes. This skill is vital when data are missing, as it enables reconstruction of lost results and validation of hypotheses about gene number and interaction.