Sister chromatids are best described as two DNA molecules that have:
a. different genes in a different order with different alleles.
b. the same genes in the same order with different alleles.
c. different genes in the same order with different alleles.
d. the same genes in the same order with the same alleles.
The Correct Answer and Explanation is:
The correct answer is b. the same genes in the same order with different alleles.
Explanation:
Sister chromatids are the two identical copies of a chromosome that are formed during DNA replication in the S-phase of the cell cycle. Each chromatid contains a complete, identical set of genes arranged in the same order along the chromosome. These two chromatids are connected by a structure called the centromere.
However, although the sister chromatids are identical in terms of the genes they carry and their order, the alleles of these genes may differ. Alleles are different versions of a gene, and they can result from mutations or inherited variations. For example, one sister chromatid may carry an allele for a particular gene that codes for a blue eye color, while the other sister chromatid may carry an allele for brown eye color. Despite these potential differences in alleles, the order of the genes on the chromatids remains the same.
Now, let’s break down why the other options are incorrect:
- a. different genes in a different order with different alleles: This describes non-sister chromatids (chromatids from homologous chromosomes) rather than sister chromatids. Non-sister chromatids may have genes in different locations, and the alleles for those genes can be different.
- c. different genes in the same order with different alleles: While the alleles may be different in sister chromatids, the genes on each chromatid are the same, and their order is identical. This option incorrectly states that the genes are different, which is not the case.
- d. the same genes in the same order with the same alleles: This would describe two identical chromatids that have undergone no variation or mutation between them. However, in many cases, there can be variations in the alleles carried by each chromatid, so this option is too restrictive.
In summary, sister chromatids are best described as having the same genes in the same order, but with the potential for different alleles at those gene positions. This genetic diversity is important for processes such as meiosis and the inheritance of traits.