Which statement is true-

Options

A. Characters segregate during formation of gametes
B. All characters show true dominance
C. The characters always blend in heterozygous condition
D. Mendelian disorder are determined by or absence or excess of one or more chromosome

Answer

To determine which statement is true among the given options, we will analyze each statement based on our understanding of genetics.

### Step-by-Step Solution:

1. **Evaluate the First Statement**:
- The first statement claims that "characters segregate during the formation of gametes."
- This is true because during meiosis, homologous chromosomes (which carry alleles for the same traits) segregate into different gametes. Therefore, each gamete receives only one allele from each pair of alleles.

2. **Evaluate the Second Statement**:
- The second statement says "all characters show true dominance."
- This statement is false. Not all traits exhibit complete dominance; some traits can show incomplete dominance or co-dominance. For example, in a heterozygous condition (Tt), the recessive allele (t) does not express dominance over the dominant allele (T).

3. **Evaluate the Third Statement**:
- The third statement claims that "characters always blend in heterozygous condition."
- This is also false. In a heterozygous condition, traits can exhibit complete dominance, incomplete dominance, or co-dominance. Therefore, not all characters blend; some may show one trait over the other.

4. **Evaluate the Fourth Statement**:
- The fourth statement states that "Mendelian disorders are determined by the absence or excess of one or more chromosomes."
- This statement is misleading. Mendelian disorders are primarily caused by mutations or defects in single genes, not by chromosomal abnormalities. Chromosomal disorders (like Down syndrome) are different from Mendelian disorders.

5. **Conclusion**:
- After evaluating all four statements, we find that the first statement is the only true statement. Therefore, the correct answer is option 1.

### Final Answer:
**The true statement is: "Characters segregate during formation of gametes."**

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