An organism of the genotype AaBbCc was testcrossed to a triply recessive organism (aabbcc). The genotypes of the progeny are presented in the following table. 20 AaBbCc 20 AaBbcc 20 aabbCc 20 aabbcc 5 AabbCc 5 Aabbcc 5 aaBbCc 5 aaBbcc If these three genes were all assorting independently, how many genotypic and phenotypic classes would result in the offspring, and in what proportion, assuming simple dominance and recessiveness in each gene pair?

Verified step by step guidance

1. Identify the genotypes of the parent organisms: AaBbCc and aabbcc.
2. Determine the possible gametes produced by each parent. The AaBbCc parent can produce 2^3 = 8 different gametes (ABC, ABc, AbC, Abc, aBC, aBc, abC, abc), while the aabbcc parent can only produce one type of gamete (abc).
3. Since the aabbcc parent can only produce one type of gamete, the genotypes of the offspring will be determined by the gametes from the AaBbCc parent.
4. Calculate the number of genotypic classes: Each gene pair (A/a, B/b, C/c) can independently assort into two possible genotypes (dominant or recessive), resulting in 2^3 = 8 genotypic classes.
5. Calculate the number of phenotypic classes: Assuming simple dominance, each gene pair will result in one dominant phenotype if at least one dominant allele is present, leading to 2^3 = 8 phenotypic classes.

Key Concepts

Independent Assortment

Independent assortment is a fundamental principle of genetics stating that alleles for different genes segregate independently of one another during gamete formation. This means that the inheritance of one trait will not affect the inheritance of another, allowing for a variety of combinations in the offspring. In the context of the question, it implies that the three genes (A, B, and C) can combine in multiple ways, leading to a diverse array of genotypes and phenotypes.

Testcross

A testcross is a genetic cross performed to determine the genotype of an organism exhibiting a dominant phenotype. This is done by crossing it with a homozygous recessive individual. In this scenario, the organism with genotype AaBbCc is crossed with aabbcc, allowing the observation of offspring to infer the genetic makeup of the dominant parent based on the phenotypes of the progeny.

Genotypic and Phenotypic Ratios

Genotypic ratios refer to the relative frequencies of different genotypes in the offspring, while phenotypic ratios refer to the relative frequencies of observable traits. In this case, the question asks for the expected ratios based on the assumption of simple dominance and recessiveness. By applying the principles of independent assortment and the testcross results, one can calculate the expected number of each genotype and phenotype among the offspring.