Which of the following is not true for homologous chromosome pairs?

Options

A. They come from only one of the individual's parents
B. They usually contain slightly different versions of the same genetic information
C. They segregate from each other during meicsls I
D. They synapse during meiosis I

Answer

To determine which statement is not true for homologous chromosome pairs, let's analyze the properties of homologous chromosomes step by step.

### Step-by-Step Solution:

1. **Definition of Homologous Chromosomes**: Homologous chromosomes are pairs of chromosomes in a diploid organism that have the same structure and gene sequence but may contain different alleles (variations of a gene). One chromosome of each pair comes from the male parent and one from the female parent.

2. **Chromosome Structure**: Each homologous chromosome consists of two sister chromatids after DNA replication, which occurs during the S phase of the cell cycle. Prior to replication, in the G1 phase, each chromosome is single-stranded.

3. **Origin of Chromosomes**: One chromosome in a homologous pair is inherited from the mother (female parent) and the other from the father (male parent). This is a fundamental characteristic of homologous chromosomes.

4. **Phases of the Cell Cycle**: Homologous chromosomes are present during various phases of the cell cycle, including G1, S, G2, and M phases. During the S phase, each chromosome duplicates its DNA content, resulting in two sister chromatids for each chromosome.

5. **Meiosis and Genetic Variation**: During meiosis, homologous chromosomes undergo processes such as synapsis (pairing) and segregation. This leads to genetic variation in gametes due to the different alleles present on the homologous chromosomes.

6. **Evaluating Statements**: Given the properties of homologous chromosomes, we can evaluate the statements provided in the question. The statement that is not true will contradict the established facts about homologous chromosomes.

7. **Conclusion**: After analyzing the characteristics of homologous chromosomes, we find that the first statement is incorrect, as it may misrepresent the origin or nature of the chromosomes in the homologous pair.

### Final Answer:
The statement that is not true for homologous chromosome pairs is option number 1.

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