Music CDs are like chromosomes in that they store information in the form of microscopic pits and high places in the groves on the disk. Chromosomes store information in the sequence of nucleotides (As, Cs, Gs, and Ts) in the DNA.
As we develop the analogy, work with a partner to answer these questions.
If we think of a chromosome as a music CD:
What is a sister chromatid?
Sister chromatids contain exact copies of DNA resulting from semi-conservative DNA replication during the S phase of the cell cycle. Therefore, we would need to have an exact copy of our CD chromosome to represent a sister chromosome.
What is a gene locus?
A gene locus is a specific place or section of the DNA of a chromosome. This segment of DNA contains the genetic code to produce a particular protein. On a music CD we could use a specific track, say track 2, on our CD to represent a gene locus.
What is a homologous pair of chromosomes?
Homologous chromosomes contain the same sequence of gene loci for the same proteins or characteristics. You get one of each homologous chromosome from each of your parents. You get one #1, one #2, one #3, etc. from Mom and another set of all the chromosome types from your dad. In the CD chromosome analogy, we would need a second CD with the same songs in the same order, but some of the songs could be different versions.
What is an allele?
An allele is a variant form of a gene. It is actually a slightly different version of a gene - a slightly different sequence of bases in the DNA of the gene. The variations that produce alleles are the result of gene mutations that change the DNA sequence. For our CD analogy, we would need two versions of the same song occuping the same track number on our two similar CDs. The two song versions might be only slightly different, say the same song by the same artist, but a slightly different version. The song might be very different, say the same song done by a different artist, or in an entirely different style.
What is the product of a music CD "allele"?
The CD allele product would be the music you hear when the CD is played.
What is the product of a real chromosome allele?
Real alleles contain the DNA code to produce one of possibly many versions of the protein produced by the various alleles of the gene.
This analogy was inspired by the release of Shania Twain's CD, "UP!". The CD set has two discs, each with 19 songs recorded by Shania. Both discs include the same 19 songs in the same order, but one disk was recorded in a "Pop" style, while the other was recorded in a "Country" style. We'll let you decide whether it is the pop or country version of the CD "alleles" that are "dominant" or "recessive".
