Chromosome numbers are usually constant within a species but vary widely between species without measuring complexity, evolutionary progress, or organism type.
Coverage 2016–2022 · Updated 15 Jul 2026
Chromosome number is usually constant within a species but varies widely between species. Humans have 46 chromosomes and chimpanzees have 48; diploid chromosome numbers are normally even because chromosomes occur as homologous pairs.
Karyotyping records the number and structural appearance of chromosomes. A karyogram is the ordered image produced by pairing homologous chromosomes and arranging them using length, banding pattern and centromere position.
A karyogram can reveal chromosome-number differences and structural similarities. Evidence for human chromosome 2 fusion includes its correspondence to two ancestral ape chromosomes, internal telomeric sequences at the predicted fusion site and remnants of a second centromere.
When pairing chromosomes in a karyogram, first match banding patterns, then confirm comparable length and centromere position rather than relying on size alone.
The observations support a testable fusion hypothesis; they should not be described as proof based only on humans having two fewer chromosomes than chimpanzees.
This objective is assessed through structured response, commonly using State.
State
Build the answer around this relationship: Diploid chromosome number is usually constant within a species.
Treating chromosome number as a measure of organism complexity or evolutionary progress.
Representative question
State the chromosome number in this gorilla.
For SL, A3.1 is really one evidence map. Variation explains why individuals differ. Morphology and binomial nomenclature help group and name organisms. The biological species concept uses interbreeding and fertile offspring, but boundaries can be difficult during gradual speciation. Chromosomes and karyograms add cellular evidence. Genomes, SNPs, genome size, and whole genome sequencing add molecular evidence. The skill is choosing the right evidence for the question.
