If two chromosomes of a species are the same length and have similar centromere placements and yet are not homologous, what is different about them?

Verified step by step guidance

1. Step 1: Understand the definition of homologous chromosomes. Homologous chromosomes are pairs of chromosomes that have the same length, centromere position, and carry the same genes in the same order, but may have different alleles.
2. Step 2: Recognize that the problem states the chromosomes have the same length and similar centromere placement, which are physical characteristics, but they are not homologous.
3. Step 3: Consider what makes chromosomes homologous beyond physical appearance. Homologous chromosomes share the same gene loci (positions of genes) and gene content.
4. Step 4: Since these chromosomes are not homologous despite similar size and centromere position, the difference must lie in their gene content or gene sequence — they carry different genes or different arrangements of genes.
5. Step 5: Conclude that the chromosomes are likely non-homologous chromosomes (non-homologs) that are similar in morphology but differ in genetic information, such as chromosomes from different chromosome pairs or sex chromosomes.

Key Concepts

Chromosome Homology

Homologous chromosomes are pairs that have the same genes arranged in the same order, one inherited from each parent. They pair during meiosis and carry alleles for the same traits, even if the alleles differ. Non-homologous chromosomes differ in gene content and do not pair during meiosis.

Chromosome Structure and Morphology

Chromosomes can be similar in size and centromere position (metacentric, submetacentric, etc.), which defines their morphology. However, similar morphology does not guarantee homology, as chromosomes may differ in gene sequences and content despite looking alike under a microscope.

Gene Content and Sequence Variation

The key difference between non-homologous chromosomes lies in their gene content and DNA sequence. Even if chromosomes appear similar structurally, they carry different sets of genes and sequences, which determines their unique identity and function within the genome.