Protein Synthesis

In real time, no less.

Polygenic inheritance

Polygenic inheritance is a pattern responsible for many features that seem simple on the surface. Many traits such as height, shape, weight, color, and metabolic rate are governed by the cumulative effects of many genes. Polygenic traits are not expressed as absolute or discrete characters, as was the case with Mendel's pea plant traits. Instead, polygenic traits are recognizable by their expression as a gradation of small differences (a continuous variation).



The results form a bell shaped curve, with a mean value and extremes in either direction.

Height in humans is a polygenic trait, as is color in wheat kernels.


Height in humans is NOT discontinuous. If you line up the entire class a continuum of variation is evident, with an average height and extremes in variation (very short [vertically challenged?] and very tall [vertically enhanced]).

Traits showing continuous variation are usually controlled by the additive effects of two or more separate gene pairs. This is an example of polygenic inheritance. The inheritance of EACH gene follows Mendelian rules.

Usually polygenic traits are distinguished by:

1. Traits are usually quantified by measurement rather than counting.


2. Two or more gene pairs contribute to the phenotype.
   
3. Phenotypic expression of polygenic traits varies over a wide range.
   

Human polygenic traits include:

• Height
  
• SLE (Lupus) an autoimmune disease


• Weight
  
• Eye Color
  
• Intelligence


• Skin Color


• Many forms of behaviour
  

The following diagrams illustrate the process of polygenic inheritance of skin colour in humans.

In this example, the trait (skin colour) is controlled by 3 genes.

The first cross is between an homozygous recessive indivivdual and an homzygous dominant indivivdual.

Click here to view graphics about human polygenic inheritance from McGill University's Genetics pages.

Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (http://www.sinauer.com/) and WH Freeman (http://www.whfreeman.com/), used with permission.

Mendelian genetics

Here is a thorough look at Mendelian genetics

For level 3 Biology students, the links to chi-squared test, modifier genes and penetrance and expressivity on the left hand side are beyond the scope of the course, but everything else is recommended.

Study questions 1 - 9 are worthwhile in assessing understanding.

The role of DNA in gene expression

Every new cell that appears after cell division must have access to instructions, so that it can function as a living entity. The existence of cell lines through time is a consequence of the ability of DNA to replicate. Copies of this informative molecule are made and placed into new cellular structures. The genes can be expressed and the cell will carry out functions commensurate with the machinery produced by that gene expression.

Guess the Poo

The following quiz comes from "Adventures in Ethics and Science", of all places.

For each of the following dung samples,

(1) what is the animal that produced it,

and

(2) what facts about the animal (in terms of its diet, digestive system, etc.) helped you identify it as the source of the pictured scat

Let's try an easy one first.

What is it about those scats that makes you think they come from an elephant?

Now use that same logic to identify the culprits of these beauties:

The 375 Million Year Old Rose of Tiktaalik

In 2006 an incredible fossil discovery was made of a very important "missing link" - one of those transitional fossils that help scientists piece together major developments in the evolutionary history of life on Earth.

In this case, the fossil was Tiktaalik roseae, an extinct species of sarcopterygian fish. The Sarcopterygii are the lobed-finned fish, an ancient group of fish that are survived today by the lungfish and the "living fossil", the coelacanth, as well as you and me and all other tetrapods. Note the family resemblance...

The University of Chicago has an amazing site that explores the fossil and the science of palaeontology.

Here is an interview with one of the scientists who hunted, located and extracted this muscular fishapod. I recommend this for insights into exactly how one goes about finding fossils.

What might and probably will happen when you die...

Thump the sky and celebrate life. Yes! I'm an organism on this planet. Fleeting as it may be, I will play my part in the forward tumble of generations. We are stepping stones for the leapfrogging double helix. But not all falls to ashes and dust.
Some things do not rot!

History must record our passing, since we will not end up in bogs, and our families or the police or the doctors will sign our last certificate.