Question

How many different DNA molecule classes does a person have?

Books always refer to human DNA as a unique molecule, and two different humans generally have different DNA molecules. But how many different types of DNA molecule does a person have?

In order to make this more understandable, let's give a physical/mathematical definition of molecule equivalence classes. Two molecules are in the same equivalence class if they have the same atoms in the same relative position to each other. And we say these two molecules are equivalent. In other word they are chemical clones of each other, like two $H_2O$ molecules are equivalent.

My question is this: how many equivalence classes of DNA does one human have (before being damaged or mutated)? 1, 23, 46, 92 or another number? Does a human have 46 or 92 different kinds of DNA molecules or just one that wraps differently to give different chromosomes? The same question could be given for a whole person or a single human cell.

Yes, I have looked on the internet and even asked a biologist. It seems the answers are always confusing to me because of the definition of the terms. What biologists seem to call the DNA molecule seems to be an ensemble of different equivalence classes of molecules, and I am finding this confusing.

Answer 1

A human has 46 chromosomes, each with a unique sequence, leading to 46 distinctive equivalence classes of DNA molecules in somatic cells, before considering mutations or damage.

Step-by-step explanation:

Humans possess 46 chromosomes, which equate to 23 pairs when accounted as matched sets from each parent. Each chromosome can be considered a unique DNA molecule within the equivalence class framework as each has a different sequence and size, leading to 23 distinct equivalence classes for the chromosomes present in a somatic cell. However, we must note the presence of two types of chromosomes: autosomal and sex chromosomes. Autosomal chromosomes are matched pairs in both sexes, while sex chromosomes determine an individual's sex and can differ between males (XY) and females (XX).

Gametes or sex cells, such as sperm and eggs, are haploid, meaning they have just one set of chromosomes, totaling 23 unique DNA molecules or equivalence classes. Therefore, if we account for a somatic cell, there would be 46 different DNA molecules if we consider each chromosome unique, or 23 if we consider the paired nature (homologous chromosomes) of autosomal chromosomes and only one sex chromosome pair. Ultimately, since each chromosome carries different genetic information, we assert that there are 46 different equivalence classes of DNA molecules in a diploid human cell, before any damage or mutations occur.