**1.1.3 The segment of a chromosome that codes for a particular characteristic.**
The correct answer is **B. Gene**. A gene is a specific sequence of DNA that contains the instructions for making a particular protein or RNA molecule, which in turn leads to a specific trait or characteristic in an organism. Genes are located on chromosomes and are responsible for the inheritance of traits from parents to offspring.
---
**1.2. Give the correct biological term for each of the following descriptions.**
1. **1.2.1. Allele that is only expressed in the homozygous state.**
The correct term for this description is **Recessive Allele**. A recessive allele is one that is only expressed when an individual has two copies (is homozygous) of that allele. In a heterozygous individual (having one dominant and one recessive allele), the dominant allele will mask the expression of the recessive allele.
2. **1.2.2. The study of heredity and variation in organisms.**
The correct term for this description is **Genetics**. Genetics is the branch of biology that focuses on the study of genes, genetic variation, and heredity in living organisms. It explores how traits are passed from parents to offspring and how genetic information is inherited and expressed.
3. **1.2.3. The physical and functional expression of a gene.**
The correct term for this description is **Phenotype**. Phenotype refers to the observable physical, physiological, and behavioral traits of an organism that result from the interaction between its genetic makeup (genotype) and the environment. It is what we can see or measure in an individual, such as eye color, height, or blood type.
These terms are fundamental in understanding genetics and how traits are inherited and expressed in organisms.
