Complete question:
Question: Contrast the genetic content and the origin of sister versus nonsister chromatids during their earliest appearance in prophase I of meiosis.
a) Sister chromatids are genetically similar, except where mutations may have occurred during DNA replication. Nonsister chromatids are genetically dissimilar.
b. Sister chromatids are genetically identical, except where mutations may have occurred during DNA replication. Nonsister chromatids are genetically similar if on homologous chromosomes and genetically dissimilar if on nonhomologous chromosomes.
c. Sister chromatids are genetically identical, except where mutations may have occurred during DNA replication. Nonsister chromatids are genetically similar.
d. Sister chromatids are not genetically similar, except where mutations may have occured during DNA replication. Nonsister chromatids are genetically similar if on homologous chromosomes and genetically dissimilar if on nonhomologous chromosomes.
Answer:
b. Sister chromatids are genetically identical, except where mutations may have occurred during DNA replication. Nonsister chromatids are genetically similar if on homologous chromosomes and genetically dissimilar if on nonhomologous chromosomes.
Explanation:
A chromosome has two chromatids after the S phase of the cell cycle. The replicated DNA molecules are accommodated in the sister chromatids. Therefore, two chromatids of a chromosome carry the identical DNA molecule and are genetically identical to each other. The sister chromatids may carry different genes if one or more mutation occurs in their DNA.
Two chromatids of two different chromosomes are called non-sister chromatids. Homologous chromosomes are the chromosomes that are similar in morphology and genetic constitution. Therefore, two chromatids of a homologous pair are also non-sister chromatids but have genetically identical sequences. For example, the two non-sister chromatids of the pair of chromosome 21 in humans carry the alleles for the same genes.
However, the non-sister chromatids that belong to nonhomologous chromosomes carry different genes and are not genetically identical.
