I'm actually currently studying physics but this came up in my textbook (taken from Giancoli 7th edition section 16-10):

The random (thermal) velocities of molecules in a cell affect cloning. When a bacterial cell divides, the two new bacteria have nearly identical DNA. Even if the DNA were perfectly identical, the two new bacteria would not end up behaving in exactly the same way. Long protein, DNA, and RNA molecules get bumped into different shapes, and even the expression of genes can thus be different. Loosely held parts of large molecules such as a methyl group can also be knocked off by a strong collision with another molecule. Hence, cloned organisms are not identical, even if their DNA were identical. Indeed, there can not really be genetic determinism.

I'm aware of different biological processes that can affect gene expression but this is random kinetic motion! Would you call this one of the epigenetic mechanisms that can affect gene expression? If so it would underlie ALL epigenetic mechanisms because all molecules have random kinetic motion.

  • 1
    $\begingroup$ Eoigenetics requires chemical modificatios. I guess "stochastic" expression will convey the process you are describing but you will have to provide context. $\endgroup$
    – Roni Saiba
    Mar 28, 2018 at 1:15

2 Answers 2


The two terms of main interest to you

Cellular noise

Cellular noise is random variability in quantities arising in cellular biology. For example, cells which are genetically identical, even within the same tissue, are often observed to have different expression levels of proteins, different sizes and structures. These apparently random differences can have important biological and medical consequences

Cellular noise was originally, and is still often, examined in the context of gene expression levels – either the concentration or copy number of the products of genes within and between cells. As gene expression levels are responsible for many fundamental properties in cellular biology, including cells' physical appearance, behaviour in response to stimuli, and ability to process information and control internal processes, the presence of noise in gene expression has profound implications for many processes in cellular biology.

There is also the term developmental noise.

Developmental noise is a concept within developmental biology in which the phenotype varies between individuals even though both the genotypes and the environmental factors are the same for all of them. Contributing factors include stochastic gene expression and other sources of cellular noise.

Developmental noise is often sounds like a synonym of cellular noise, but it is supposed to include more processes that are causing phenotypic variation then cellular noise. For example, it is common to consider "micro-environmental variation" as being part of developmental noise and not of cellular noise.

The way your phrased your question

In your question you describe only sources of cellular noise. However, you end up saying Hence, cloned organisms are not identical, even if their DNA were identical. I just want to highlight that, there are other reasons than cellular noise for which two clones differ. These include micro-environmental variance, physiological noise, epigenetic variance and macro-environmental variance (often just called environmental variance). Note that I had never encountered the term "physiological noise" before, I just made it up but I wanted to highlight that noise also happen in among cells processes, not only within cells processes.

Intro to quantitative genetics

For a short introduction to quantitative genetics and the different sources of phenotypic variance (genetic variance, environmental variance, developmental noise, etc..) and how the concept of heritability fits into this discussion, please have a look at the post Why is a heritability coefficient not an index of how “genetic” something is?

  • $\begingroup$ Thank you for the taking the time to provide this detailed answer. $\endgroup$
    – user41406
    Mar 29, 2018 at 4:43
  • $\begingroup$ You're welcome. If you think your question has been answered, you can click on the checkmark next to the answer. $\endgroup$
    – Remi.b
    Mar 29, 2018 at 14:51

Heterogeneous is the term you're looking for I believe.

From Wikipedia,

A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, size, weight, height, distribution, texture, language, income, disease, temperature, radioactivity, architectural design, etc.); one that is heterogeneous is distinctly nonuniform in one of these qualities.

  • 1
    $\begingroup$ If you're going to downvote, at least explain why. $\endgroup$
    – Eppicurt
    Mar 28, 2018 at 6:05
  • 1
    $\begingroup$ Because all living organisms are a heterogeneous mess of proteins, DNA, RNA, lipids, carbohydrates, ions, you name it. The term "stochastic processes" suggested above is closer to the notion referred to in the question. $\endgroup$
    – Guillaume
    Mar 28, 2018 at 13:31

You must log in to answer this question.