Sister chromatids of a chromosome have :

Options

A. Different genes at the same locus
B. Different alleles at the same gene at the same locus
C. Same alleles of the same gene at the same locus
D. Same alleles at different Loci.

Answer

To solve the question regarding what sister chromatids of a chromosome have, we can follow these steps:

### Step 1: Understand the Structure of Chromosomes
- Chromosomes are made up of DNA and proteins, and they exist in pairs in diploid organisms.
- Each chromosome consists of two identical halves known as sister chromatids, which are joined at a region called the centromere.

**Hint:** Remember that sister chromatids are identical copies of a single chromosome.

### Step 2: Define Sister Chromatids
- Sister chromatids are formed during the S phase of the cell cycle when DNA is replicated.
- Each sister chromatid contains the same genetic information as the other, meaning they are identical in terms of the DNA sequence.

**Hint:** Think of sister chromatids as two identical twins; they share the same genetic makeup.

### Step 3: Identify the Genetic Content
- Since sister chromatids are identical, they carry the same alleles for each gene located at the same loci.
- This means that if a gene has multiple forms (alleles), both sister chromatids will have the same allele at that locus.

**Hint:** Focus on the idea that sister chromatids are exact copies, so their genetic information must be the same.

### Step 4: Analyze the Question Options
- The question asks what sister chromatids have:
1. Different genes at the same locus - Incorrect
2. Different alleles at the same gene at the same locus - Incorrect (sister chromatids have the same alleles)
3. Same alleles at the same gene at the same locus - Correct
4. Same alleles at different loci - Incorrect

**Hint:** Compare each option carefully with the definition of sister chromatids.

### Step 5: Conclusion
- The correct answer is that sister chromatids have the same alleles at the same gene at the same locus.

**Final Answer:** Sister chromatids of a chromosome have the same alleles at the same gene at the same locus.