34- The Tuatara

On the show today, we discuss the tuatara- two species of reptile which are the final representatives of an ancient lineage.

Sources for this episode: 1) Cooke, F., Dingle, H., Hutchinson, S., McKay, G., Schodde, R., Tait, N. and Vogt, R. (2008), The Encyclopedia of Animals: A Complete Visual Guide (p.370). Sydney: Weldon Owen Pty Ltd. 2) Thain, M. and Hickman, M. (2014), Dictionary of Biology (Eleventh Edition) (p.622). London: Penguin Books Ltd. 3) Author unknown, Wikipedia (date unknown), Rhynchocephalia (online) [Accessed 28/03/2021]. 4) Blythe, C. A., Encyclopaedia Britannica (2021), New Zealand (online) [Accessed 28/03/2021]. 5) Campbell, N. A., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Reece, J. B. (2018), Biology: a global approach, 11th edition (Global Edition), Harlow, Pearson Education Limited: p.788- 789.

33- Lethal Alleles

At A Level, we are taught that dominant: recessive traits are in a 3:1 ratio for any trait in which only one gene encodes for it. However, it’s not always that simple. Enter lethal alleles…

Sources for this episode: 1) Author unknown, Wikipedia (date unknown), Lethal allele (online) [Accessed 26/03/2021]. 2) Author unknown, Wikipedia (date unknown), Manx cat (online) [Accessed 27/03/2021]. 3) Gao, Z., Waggoner, D., Stephens, M., Ober, C. and Przeworski, M. (2015), An Estimate of the Average Number of Recessive Lethal Mutations Carried by Humans. Genetics 199: 1243- 1254. 4) Roos, R. A. C. (2010), Huntingdon’s disease: a clinical review. Orphanet Journal of Rare Diseases 2010 5:40. 5) For an example of the deleterious effects of inbreeding as discussed in today’s episode, see the Wikipedia or Encyclopaedia Britannica pages on Charles II of Spain. I might come back to him and his ailments in a separate episode, but until then he will also serve as a good example.

32- Trisomies and Non-Disjunction

Usually, we get two copies of each chromosome. However, the finely tuned process of meiosis and fertilisation can go awry such that a new zygote ends up with three copies. Depending on the chromosome, this can have serious consequences…

Sources for this episode: 1) For an explanation of non-disjunction which I found helpful when I was at sixth form, see: Amoeba Sisters, YouTube (2017), Meiosis (Updated) (online) [Accessed 25/03/2021]. 2) NHS website, Edwards’ syndrome (trisomy 18) (online) [Accessed 25/03/2021]. 3) Xu, X., Zhang, X., Han, J.-W., Adamu, Y. and Zhang, B. (2020), Potential Increased Risk of Trisomy 18 Observed After a Fertilizer Warehouse Fire in Brazos County and TX. International Journal of Environmental Research and Public Health 17: 2561- 2571.

31- Choanoflagellates

We often think about animals as an insular group. However, as with any genetic grouping, animals do have close relatives. On the show today, we discuss choanoflagellates- considered the closest relatives to animals today, and possibly a good candidate for what the common ancestor of all animals would have looked like.

Sources for this episode: 1) Campbell, N. A., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Reece, J. B. (2018), Biology: a global approach, 11th edition (Global Edition), Harlow, Pearson Education Limited. 2) The Editors, Encyclopaedia Britannica (2021), Choanoflagellate (online) [Accessed 13/03/2021]. 3) Marshall, M., New Scientist (2009), Timeline: The evolution of life (online) [Accessed 13/03/2021]. 4) Holland, S. M., Encyclopaedia Britannica (2021), Ordovician Period (online) [Accessed 13/03/2021]. 5) Philippe, H., et al. (2009), Phylogenomics Revives Traditional Views on Deep Animal Relationships. Current Biology 19: 706- 712.

30- Measures of Diversity

Biodiversity is often mentioned as one concept in popular culture. However, it can be split into different components depending on who you ask. Today, we’re going to explore two different ways of chopping biodiversity up.

Sources for this episode: 1) Author unknown, Wikipedia (date unknown), Gamma diversity (online) [Accessed 06/03/2021]. 2) Cain, M. L., Bowman, W. D. and Hacker, S. D. (2011), Ecology (2nd edition). Sunderland: Sinauer Associates Ltd. 3) For a formula for Shannon’s index of biodiversity (which I’m going to try and discuss in a future episode), see: Fullick A., Locke, J. and Bircher, P. (2015), A Level Biology for OCR A. Oxford: Oxford University Press.

29- Sympatric Speciation

This week, we’re going to discuss sympatric speciation- the counterpart to allopatric speciation where no physical barrier is needed.

Sources for this episode: 1) Thain, M., and Hickman, M. (2014), The Penguin Dictionary of Biology, 11th edition. London: Penguin Publishing Group. 2) Campbell, N. A., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Reece, J. B. (2018), Biology: a global approach, 11th edition (Global Edition), Harlow, Pearson Education Limited. 3) Author unknown, Understanding Evolution (berkeley.edu), Sympatric speciation (online) [Accessed 28/02/2021]. 4) Author unknown, National Geographic (date unknown), Speciation (online) [Accessed 28/02/2021].

Bonus- A Biographical Sketch of an Infant (1877)

Another bonus episode! This time, I’m going to focus on a less well-known story from the Darwin family. Specifically, let’s look at William Erasmus Darwin, the eldest child of the family. In 1877, Darwin published an article about his observations of William’s development.

Sources for this episode: 1) Author unknown, Wikipedia (date unknown), William Erasmus Darwin (online) [Accessed 25/03/2021]. 2) Darwin, C. R. (1877), A biographical sketch of an infant. Scientific American Supplement 86: 1373- 1374 (online, scan of the original available at JF Ptak Science Posts) [Accessed 25/03/2021]. 3) Author unknown, Wikipedia (date unknown), The Descent of Man (online) [Accessed 26/03/2021 for the date].

28- Speciation and the Great Wall of China

The Great Wall of China is one of the most imposing monuments humanity has ever created- after all, it’s not for nothing that the claim goes around that you can see it from space. However, it’s not just an effective barrier for humans. In fact, a 2003 study indicates that it’s causing speciation in the region…

Sources for this episode: 1) Su, H., Qu., L.-J., He, K., Zhang, Z., Wang, J., Chen, Z. and Gu, H. (2003), The Great Wall of China: a physical barrier to gene flow? Heredity 90: 212- 219. 2) The Editors, Encyclopaedia Britannica (2021), Great Wall of China (online) [Accessed 19/02/2021]. 3)Campbell, N. A., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V. and Reece, J. B. (2018), Biology: a global approach, 11th edition (Global Edition), Harlow, Pearson Education Limited 4) Oltermann, P., et al., The Guardian/Observer (2010), The Ancient World (booklet series), Day 6: China. Associated with the British Museum.

27- Twin Types

We’re always taught that twins can either be identical or non-identical. But what is the basis for this? And is there ever a situation where twin type is not quite so binary?

Sources for this episode: 1) Davis, N., the Guardian (2019), Scientists stunned by discovery of ‘semi-identical’ twins (online) [Accessed 07/02/2021]. 2) Author unknown, BBC (2019), Semi-identical twins ‘identified for only the second time’ (online) [Accessed 07/02/2021]. 3) Author unknown, Wikipedia (date unknown), Twin (online) [Accessed 08/02/2021].

26- The Anthropocene

The term ‘Anthropocene’ (roughly translated as ‘Age of Man’) is a term that is sometimes thrown about on the radio or in science. But what is it exactly? As we’ll see today, the concept itself is relatively simpler, but nailing down the specifics is somewhat harder than it seems…

Sources for this episode: 1) Author unknown, Encyclopaedia Britannica (2020), Anthropocene Epoch (online) [Accessed 30/01/2021]. 2) Ashley, S., National Trust (date unknown), What is the Anthropocene? (online) [Accessed 30/01/2021]. 3) Author unknown, Wikipedia (date unknown), Chinese industralization (online) [Accessed 02/02/2021].