Tuesday Morning Comics

Hi all!  I've been spending a lot of time on here writing about science instead of science and religion (although I would argue that to discuss science and religion, religious people need to understand science, and scientists need to understand religion, which is what motivates these posts), so as I prepare to leave Quebec I wanted to share a science/religion comic with you.  I find these things all over the internet, and I am amassing a collection of them.  I'll post one from time to time.  

Variation

Humans come in different shapes, sizes, colours, temperaments, propensities to disease and the like.  Although the human population continues to increase, we seem to never run out of variations on the human ‘type’.  All of the dog breeds of the world ultimately descend from the same wolf ancestor.  The bulldog, the terrier, the great Dane, the German shepherd, were all produced when humans took existing varieties and made some choice selections.  The same goes for our agricultural products: kale, cabbage, broccoli and cauliflower all descend from the same wild cabbage species.  The fruit fly Drosophila pseudoobscura, according to Dobzhansky, has seven different types of Y chromosomes; there are strains of wheat with 7, 14 or 21 chromosomes.

Without variation, there can be no evolution.  Dobzhansky spends the first four chapters of his book driving this point home, because it is that essential.  If variation was not continually being produced, there would be no differences between individuals; without differences between individuals, there would be no selection; and without selection, there would be no adaptation.

The Joy of Chromosomes (Part 3)

Last week we talked a bit about chromosomes, the process of sperm/egg/pollen formation, and how missteps during meiosis can lead to chromosomal mutations in terms of numbers of chromosomes.  We defined haploidy and polyploidy as the loss or gain of an entire set of chromosomes, and monosomy and polysomy as the loss or gain of a single chromosome.   We also saw how species and races contain variability, not just in the content of their DNA, but also in the number of chromosomes that they have.  Humans, for instance, have one less chromosome than the other great apes; a single species of Iranian climbing weed has populations with vastly different numbers of chromosomes.

Today I’d like to continue following the layout of Dobzhansky’s book, Genetics and the Origin of Species, by continuing to categorize chromosomal mutations according to changes in their structure.  Structural mutations do not affect the number of chromosomes within an organism, but rather alter the layout of genes within a chromosome.  Structural mutations can be classified as follows:

Chromosomes, Chimps, and Human Evolution

I have been working hard in Quebec collecting my microarray data, and between that and a great visit from my dad over father's day, I simply have not had time to write the next article on chromosomes.  But in anticipation of the evolutionary importance of chromosomal mutations, here is a video clip from evolutionist and Catholic Kenneth Miller, discussing what I consider to be the single most powerful evidence for the evolution of humans from a primate ancestor, and it involves a chromosomal mutation.

The court case he refers to at the beginning is the trial that occurred in Dover, Pennsylvania, in 2004 over the religious nature of Intelligent Design.  Kenneth Miller testified against the school board, arguing that ID has no place in a science classroom.  The part of the lecture I am showing was part of a tour he gave after the court case, explaining exactly what he, as a religious man and a scientist, has serious issues with ID.

Enjoy.

The Joy of Chromosomes (Part 2)

Chromosomes are the carriers of genes.  Each chromosome acts as an individual, faithfully passing its structure on to its offspring each time a cell divides.  But ‘faithfulness’ has its limits – occasionally a ‘mutant’ chromosome is produced that will then be replicated.  The number of chromosomes within a cell can also be faithfully replicated down the generations, but occasionally they too can change.

When we talk about chromosomal mutations, then, we need to differentiate between changes in chromosome number and structure.  Today, we will talk about number.

The Joy of Chromosomes (Part 1)

So, you have found yourself transported in time to the 1930s, and you have a strong desire to study mutations?  But those uncivilized brutes have yet to develop methods for examining changes in DNA?  Never fear!  You can do the second-best thing, and rediscover everyone’s favourite pastime: karyotyping!

All Species Are the Products of Mutations

Summary so far

To recap our story: evolutionary biology’s ultimate quest is to explain the diversity and discontinuity we see in the natural world.  A whale and a mouse are two very different things; they do not insensibly blend into one another.  Yet despite their discontinuity, they also have very similar body structures.  What accounts for this?  And why in less extreme cases is this discontinuity at times fuzzy, such that we have difficulty telling if two different populations are different species, or merely varieties of the same species?

Mutations: The Good, the Bad, and the Neutral (Part 5)

Lesson 5: A single mutation cannot create a new species

There was some debate during Dobzhansky’s time about whether new species could be formed through the birth of rare ‘monsters’.  Such monsters would be the product of a mutation, and would be effectively shut off from the rest of the population, forming their own species.  This theory was called saltationism.  Saltationists argued that a single mutation can have a very large effect.  A mutation somehow produces fundamental changes to the species, such that a new species is formed.

Mutations: The Good, the Bad, and the Neutral (Part 4)

We have so far learned from Dobzhansky that:

1.       Mutations are common in nature and are the source of all diversity

2.       Mutations can be really bad, to the point of being lethal, but there is a gradient from bad to good; bad mutations can hide as recessives within a population

3.       Environmental change (or a change in the genetic background) can turn a ‘bad’ mutation good, and a ‘good’ mutation bad.  Mutational value is contextual.

Lesson 4 – A single mutation can have a multitude of effects

Mutations: The Good, the Bad, and the Neutral (Part 3)

Lesson 3 – The value of a mutation (good, bad, or neutral) changes with the environment.  A mutation that appears to be bad in one context, might be good in another.

So far we have seen that mutations are common enough in nature, that bad mutations can hide as recessives within a population (contributing to the population’s overall genetic diversity), and that mutations can have anywhere from hugely negative effects (ie lethal mutations) to almost negligible effects.

What Dobzhansky has not yet shown is that mutations can be beneficial to the organism.

Mutations: The Good, the Bad, and the Neutral (Part 2)

Lesson 2: ‘Bad’ is a relative term.  Some mutations are worse than others, and even really bad mutations can hide in a population.

As we saw yesterday, mutations occur frequently in nature.  Inheritance of parental traits is conservative, in that it is usually quite faithful; but if it is completely faithful, there can never be variation in a trait.  Mutations counter this ‘copy fidelity’, acting as an opposing ‘force’ that produces variation.  Dobzhansky inferred from this that all of the heritable variation that we see in nature is due to mutations that have occurred either recently or in the remote past.