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| |
 | Mitosis: Chromosome Replication & Division | ||
| Issue | Naive Idea* | Scientific Idea |
|---|---|---|
| Replicated Chromosome | The familiar X-shaped structure seen in a light microscope is a 'basic' (unreplicated) chromosome. | The X-shaped structures seen in a light microscope are condensed, replicated chromosomes containing two identical DNA double helices. |
| Unreplicated Chromosome | A chromosome is a chromosome - there is little differentiation between replicated and unreplicated states. | In late anaphase and G1 of interphase, a chromosome is unreplicated and consists of a single DNA double helix. |
| 'Chromosome Pairs' | The X-shaped chromosomes are homologous chromosome pairs. | The X-shaped structures are unpaired, replicated chromosomes. Pairing of homologous chromosomes does not occur during mitosis. |
| 'Unpaired Chromosomes' | Unreplicated chromosomes seen in anaphase are unpaired chromosomes. | These are simply unreplicated chromosomes, and this is the only time they are condensed and therefore visible. |
| Distribution | As an extension of the above model, the two non-identical homologous chromosomes in a parent cell go to separate daughter cells. | In anaphase, the identical chromatids of a replicated chromosome go to separate daughter cells. Each daughter cell gets a complete copy of the chromosomes in the parent cell. |
| Gene/Allele | Gene and allele are essentially the same thing. | A gene is a segment of DNA that produces a particular product such as the enzyme amylase. In many cases, a given gene has changed (mutated) over time, so that a population might contain several alleles (variations) of the same gene. For example, allele 1 might produce a fully functional amylase, allele 2 a partially functional amylase, and allele 3 a non-functional amylase. |
| Allele Distribution | If there are three alleles in a population, an individual may have three alleles. | Each individual receives just two alleles of each gene, one from each parent, no matter how many types of alleles exist in a population. |
* A misconception or alternative idea has three primary features: it is a cognitive idea that differs in a significant way from the scientific idea, it is held by a sizable proportion of the population, and it is notably resistant to being taught away; it is often described as a conceptual primitive (Clement, 1982). There are many other types of errors in understanding besides misconceptions (Fisher & Lipson, 1986).
Clement, J. (1982). Students¹ preconceptions in introductory mechanics. American Journal of Physics, 50 (1), 66 - 71.
Fisher, K. M. & Lipson, J. I. (1986). Twenty questions about student errors. Journal of Research in Science Teaching, 23 (9), 783-803.
