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Botany: A Blooming History (Part 3) - Plant genetics
*Note - sound goes out in a couple places
Plant genetics - new tool - production of new and improved varieties of staple crops
All plant diversity exists ultimately for reproduction
How does plant variety come about? - searching for mechanism behind plant variation and diversity - heritable traits
sexual reproduction leads to inheritance of a mix of traits from each parent
Gregor Mendel - now famous pea plant experiment - central understanding of inheritance - ratios of phenotypes are always the same
William Bateson - wants to understand inheritance - are there universal laws of inheritance in plants and animals? - field of genetics (study of genes)
chicken ratios of phenotypes again are always the same
genes from each parent contribute....dominant and recessive genes - this makes Mendel's data make sense!
with knowledge of genetics we can predict how plant crossing will play out in the resulting population
BUT...snapdragons - inheritance of flower colors are unpredictable!
Muriel Wheldale - investigates this issue with crossbreeding experiments to search for patterns in flower color - several genes (and their combinations) control color in snap dragons - same concept as Mendel's peas but just more complex!
Nikolai Valvilov - wants to produce supercrops for the USSR - collects plants from around the world (first seed bank) for this purpose - scientific approach to breeding plants using knowledge of genetics
genetics as propaganda...conflict with Stalin
scapegoat for bad USSR harvests leads to arrest and death via starvation
sacrifice of scientists in Soviet seed vault in Leningrad
Norman Borlaug - agriculturalist wheat breeder with field station in Mexico - trying to increase wheat disease resistance
breeds wheat with heavy seed heads and talk stalks - stalks are too weak and lodge (fall over) - thus wasting the grain
botanists found Japanese wheat adapted to local climate (Norin 10) - dwarf variety that grows shorter - this is crossed with the taller Mexican variety - leads to robust dwarf wheat with large seed heads - huge increase in yield
flip-side: dwarf wheat also requires more inputs (water, fertilizer, etc.) - questions about long-term sustainability
awarded Nobel Peace Prize for easing starvation (known as Green Revolution)
all crossbreeding successes to this point based on "lucky mistakes" of evolution to provide the traits needed - the next step - actually design traits into organisms directly (genetic modification)
Barbara McClintock - wants to understand how plants pass on characteristics - works extensively with corn
color patterns on seeds makes her suspect needed revision to genetics - ancestral red color comes back in corn - how are genes that have been "bred out" re-emerge???
runs breeding experiment on corn - controlled breeding
key insight - genes can be turned on and off - they don't disappear they just become "switched off" - and can be "switched on" again
Genetic Modification (GM) - We now have tools to flip these genetic "switches" - we can even moves these genes between organisms (transgenics)
case study - GM rice - C3 rice using the C4 photosynthetic pathway
one step is to increase number of veins of leaves
must extract cells that surround the veins for genetic work
Next "Green Revolution" is thought to include GM technology
An in-depth dive into Mendellian genetics. I know many of you have seen this story over and over again...I just wanted to make sure you have this resource!
polyploidy
polyploidy
A very basic introduction to polyploidy (very different from the diploid story we are used to thinking about!). Plants are particularly good at surviving (and even thriving) as polyploids. Polyploidy kills most mammals!
Some basic applications of a polyploid plant (Tragopogon)
Genetic modification techniques
Genetic modification techniques
An introduction to why we do GM of crops (not really how). Lots more resources from the Royal Society on GM can be found here
The first stage in making a GM plant requires transfer of DNA into a plant cell. One of the methods used to transfer DNA is to coat the surface of small metal particles with the relevant DNA fragment, and bombard the particles into the plant cells. Another method is to use a bacterium or virus. There are many viruses and bacteria that transfer their DNA into a host cell as a normal part of their life cycle. For GM plants, the bacterium most frequently used is called Agrobacterium tumefaciens. The gene of interest is transferred into the bacterium and the bacterial cells then transfer the new DNA to the genome of the plant cells. The plant cells that have successfully taken up the DNA are then grown to create a new plant. This is possible because individual plant cells have an impressive capacity to generate entire plants. On rare occasions, the process of DNA transfer can happen without deliberate human intervention. For example the sweet potato contains DNA sequences that were transferred thousands of years ago, from Agrobacterium bacteria into the sweet potato genome.
A very surficial look at the very new method called CRISPR - pay attention to this tech as you are going to see it pop up more and more when it comes to genetically modifying food (and other things!). Here is just one example article (I bet you can find tons!)
“Some segments of people aren’t going to care as much about how it was done...as long as they get this amazing thing they get to eat.”
other resources....
other resources....
Polyploidy: In a given area phlox can exist as diploid, tetraploid, and hexaploid! We are used to the boring old diploid and haploid life but plants do something different.....polyploidy!!!
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