Pure line breed refers to

Options

A. Heterozygosity only
B. Heterozygosity and linkage
C. Homozygosity only
D. Homozygosity and self-assortment.

Answer

### Step-by-Step Solution:

1. **Definition of Pure Line Breed**:
- A pure line breed refers to a genetic line that consists of individuals that are homozygous for specific traits. This means that all the alleles for those traits are identical.

2. **Characteristics of Pure Line**:
- In a pure line, there is no mixture of genes from different varieties or species. This results in a consistent expression of traits across generations.
- Pure lines are often referred to as true breeding lines, meaning that when individuals from this line are bred together, they produce offspring that exhibit the same traits as the parents.

3. **Example from Mendelian Genetics**:
- In Mendel's experiments, he used pure lines to study inheritance. For example, a pure line for a dominant trait (homozygous dominant, represented as TT) and a pure line for a recessive trait (homozygous recessive, represented as tt) were crossed.
- The offspring from this cross would all be heterozygous (Tt) and express the dominant trait.

4. **Homozygosity vs. Heterozygosity**:
- A pure line is characterized by homozygosity, meaning that both alleles for a trait are the same (either both dominant or both recessive).
- In contrast, heterozygous individuals (Tt) contain one dominant and one recessive allele, which leads to variation in traits and is not considered a pure line.

5. **Conclusion**:
- Therefore, a pure line breed is defined by its homozygosity, ensuring that the genetic makeup remains consistent and predictable across generations.