In human beings, where genotype AABBCC represents dark skin colour, aabbcc represents light skin colour and AaBbCc represents intermediate skin colour, the pattern of genetic inheritance can be termed as:
a) Pleiotropy and codominance
b) Pleiotropy and incomplete dominance
c) Polygenic and qualitative inheritance
d) Polygenic and quantitative inheritance

Options

A. Pleiotropy and codominance
B. Pleiotropy and incomplete dominance
C. Polygenic and qualitative inheritance
D. Polygenic and quantitative inheritance

Explanation

To solve the question regarding the genetic inheritance pattern represented by the genotypes AABBCC (dark skin color), aabbcc (light skin color), and AaBbCc (intermediate skin color), we will analyze the options provided and identify the correct terms that describe the inheritance pattern.

### Step-by-Step Solution:

1. **Understanding the Genotypes:**
- AABBCC represents dark skin color, indicating that the presence of dominant alleles (A, B, and C) leads to this phenotype.
- aabbcc represents light skin color, indicating that the presence of recessive alleles (a, b, and c) leads to this phenotype.
- AaBbCc represents intermediate skin color, showing a mix of dominant and recessive alleles.

2. **Identifying the Type of Inheritance:**
- The presence of multiple genes (A, B, and C) affecting a single trait (skin color) indicates that this is an example of **polygenic inheritance**. In polygenic inheritance, multiple genes contribute to a single phenotype.

3. **Determining the Nature of the Trait:**
- The variation in skin color from dark to light, with an intermediate phenotype, suggests that the trait is influenced by the quantity of dominant alleles present. This means that the expression of the trait is quantitative, as it varies in degree rather than being categorical.

4. **Evaluating the Options:**
- a) Pleiotropy and codominance: Incorrect, as pleiotropy involves one gene affecting multiple traits, and codominance involves both alleles being fully expressed.
- b) Pleiotropy and incomplete dominance: Incorrect for similar reasons; incomplete dominance involves blending of traits.
- c) Polygenic and qualitative inheritance: Incorrect, as qualitative inheritance refers to traits that fall into distinct categories, not a range.
- d) Polygenic and quantitative inheritance: Correct, as it describes the situation where multiple genes influence a single trait and the trait varies in degree.

5. **Conclusion:**
- The correct answer is **d) Polygenic and quantitative inheritance**.