Sex in the Garden - Plant Genetics & GM

Botany:  A Blooming History (Part 3) - Plant genetics

• 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!

The video "How Mendel's pea plants helped us understand genetics" explains the groundbreaking work of Gregor Mendel, an Austrian monk and biologist, in the 19th century. Mendel's experiments with pea plants revealed fundamental principles of heredity that laid the foundation for modern genetics.

Key points from the video:

• Mendel's Experiment: Mendel crossbred pea plants with different traits (e.g., yellow vs. green seeds) and observed the patterns of inheritance in their offspring. He found that certain traits, like yellow seed color, were dominant, while others, like green seed color, were recessive.

• Dominant and Recessive Traits: Mendel's experiments demonstrated that each trait is determined by a pair of factors (now known as alleles), one inherited from each parent. Dominant alleles mask the expression of recessive alleles.

• Genotype and Phenotype: The video introduces the terms genotype (the genetic makeup of an organism) and phenotype (the observable traits resulting from the genotype).

• Punnett Squares: The Punnett square, a simple diagram, is used to predict the possible genotypes and phenotypes of offspring based on the parents' genotypes.

• Significance of Mendel's Work: Mendel's discoveries provided the basis for understanding how traits are passed down from generation to generation and paved the way for modern genetics research.

The video concludes by emphasizing the lasting impact of Mendel's work on our understanding of genetics and its applications in various fields, including medicine, agriculture, and biotechnology.

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!

Polyploidy: A Detailed Summary with Focus on Plants

Introduction

• Ploidy: The number of complete sets of chromosomes in a cell.

• Polyploidy: The condition of having more than two sets of chromosomes.

• Prevalence: While most animals are diploid (2 sets), polyploidy is common in plants, occurring in 30-80% of angiosperms.

Types of Polyploidy

Autopolyploidy

1. • Origin: Arises from a single species.

   • Mechanism: Errors in meiosis or mitosis can lead to chromosome doubling within a species.

   • Examples: Potatoes, bananas, some watermelons.

Allopolyploidy

1. • Origin: Arises from hybridization between different species.

   • Mechanism: Hybrids are often sterile due to mismatched chromosomes, but subsequent genome doubling can restore fertility.

   • Examples: Wheat, cotton, canola, many ferns.

Mechanisms of Polyploid Formation

• Meiotic Errors: Non-disjunction of chromosomes during meiosis can produce diploid gametes, which, when fertilized, result in polyploid zygotes.

• Mitotic Errors: Endoreduplication, the replication of chromosomes without cell division, can lead to polyploid cells.

• Polyspermy: Fertilization of an egg by multiple sperm can create polyploid zygotes.

Advantages of Polyploidy in Plants

• Increased Vigor: Polyploids often exhibit larger size, faster growth, and increased stress tolerance compared to their diploid counterparts.

• Novel Traits: Polyploidy can lead to new phenotypes and increased genetic diversity, facilitating adaptation to diverse environments.

• Heterosis (Hybrid Vigor): In allopolyploids, the combination of different genomes can result in superior performance compared to the parental species.

Consequences of Polyploidy

• Genetic Isolation: Polyploids are often reproductively isolated from their diploid parents, potentially leading to speciation.

• Gene Expression Changes: Polyploidy can trigger changes in gene expression, altering various physiological and developmental processes.

• Genome Restructuring: Polyploid genomes can undergo rapid changes, including gene loss, duplication, and rearrangements, further contributing to evolutionary novelty.

Applications in Agriculture

• Crop Improvement: Polyploidization is a common tool in plant breeding to create new varieties with desirable traits like increased yield, disease resistance, or improved quality.

• Seedless Fruits: Triploid plants are often sterile, resulting in seedless fruits like watermelons and bananas.

Conclusion:

Polyploidy is a fascinating and complex phenomenon that has played a significant role in plant evolution and diversification. Understanding the mechanisms and consequences of polyploidy is essential for advancing plant breeding, agriculture, and our understanding of evolutionary processes.

Some basic applications of a polyploid plant (Tragopogon)

Polyploidy in plants is a condition where a plant has more than two complete sets of chromosomes. This video explains how it happens and why it's important, using Tragopogon (goatsbeard) as a model species to illustrate the concept.

Here's a summary to help you understand polyploidy and the significance of Tragopogon:

• Ploidy: This refers to the number of complete sets of chromosomes in a cell. Humans, for example, are diploid, meaning we have two sets.

• Polyploidy: This occurs when an organism has more than two sets of chromosomes. This can happen due to errors in cell division, like when chromosomes fail to separate properly during meiosis.

• Types of Polyploidy:

  • Autopolyploidy: This happens within a single species, where the extra chromosome sets come from the same species.

  • Allopolyploidy: This occurs when two different species hybridize, resulting in offspring with chromosome sets from both parents. This is common in plants, and Tragopogon is an excellent example of this.

• Tragopogon as a Model Species:

  • Recent and Recurrent Polyploidization: Tragopogon species have undergone polyploidization events in the recent past (within the last ~80 years), making them ideal for studying the early stages of polyploid evolution.

  • Multiple Origins: Allopolyploid Tragopogon miscellus has formed multiple times independently, allowing scientists to compare how polyploidy evolves in different lineages.

  • Observable Changes: Polyploid Tragopogon species exhibit distinct morphological differences from their diploid parents, providing visible evidence of the effects of polyploidy.

  • Genetic Tools: Tragopogon is amenable to genetic analysis, making it possible to study the underlying genetic mechanisms of polyploidization and its consequences.

• Consequences of Polyploidy:

  • Increased size and vigor: Polyploid plants often have larger cells and tissues, leading to bigger fruits, flowers, or overall plant size.

  • Novel traits: Polyploidy can create new traits that weren't present in the original parent species. This can be beneficial for adaptation and evolution, as seen in Tragopogon species.

  • Reproductive isolation: Polyploid plants may not be able to interbreed with their diploid parents, potentially leading to the formation of new species. This is a key aspect of Tragopogon's evolutionary history.

• Polyploidy in Agriculture: Polyploidy has been used by humans to create new crop varieties with desirable traits. The study of Tragopogon provides insights into how polyploidy can be harnessed for crop improvement.

The video also explains how polyploidy can be induced artificially using chemicals like colchicine. This technique is widely used in plant breeding to create new and improved crops, building on the knowledge gained from studying natural polyploids like Tragopogon.

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

• Natural Selection vs. Agriculture: Natural selection favors traits like competitiveness and defense mechanisms in plants, often conflicting with agricultural goals of maximizing yield and nutritional value.

• Genetic Improvement: Genetic improvement has been central to increasing agricultural productivity for millennia. Modern agriculture employs both traditional breeding and genetic modification (GM) techniques to achieve this goal.

• Conventional Breeding: Involves crossing plants with desirable traits to combine their genetic material and create offspring with improved characteristics. This process is time-consuming and limited by the available genetic diversity within the species or closely related species.

• Genetic Modification (GM): Enables the precise and targeted insertion of specific genes from any organism into a crop's genome. This bypasses the limitations of conventional breeding and allows for the rapid introduction of novel traits not found in the species' natural gene pool.

  • Process of Genetic Modification:

Gene Identification: Identify the gene of interest responsible for the desired trait (e.g., disease resistance, drought tolerance).

Gene Isolation: Extract the gene from the donor organism.

Gene Transfer: Insert the gene into the recipient plant's genome using various techniques like:

• • 1. • Agrobacterium-mediated transformation: Utilizing a soil bacterium to deliver the gene into plant cells.

       • Gene gun: Bombarding plant cells with DNA-coated particles.

       • CRISPR-Cas9: A precise gene-editing tool that can modify existing genes or insert new ones.

Plant Regeneration: Grow the genetically modified cells into whole plants.

Testing and Selection: Evaluate the transgenic plants for the desired trait and select the most promising lines for further breeding.

• Applications of GM:

  • Enhanced yield and nutritional value

  • Increased resistance to pests, diseases, and environmental stresses (e.g., drought, salinity)

  • Improved shelf life and processing qualities

• Safety and Regulation: GM crops undergo rigorous testing and regulation to ensure their safety for human consumption and environmental impact. While scientific consensus supports their safety, ongoing research and public discourse are essential.

• Sustainability: GM crops can contribute to sustainable agriculture by reducing pesticide use, improving resource use efficiency, and developing crops adaptable to climate change.

• Challenges and Controversies:

  • Ethical concerns about altering natural organisms and potential unintended consequences.

  • Socioeconomic concerns about corporate control of GM technology and access for small-scale farmers.

  • Need for long-term studies on environmental and health impacts.

Conclusion:

Both conventional breeding and genetic modification are valuable tools for crop improvement. The choice between them depends on the specific goals, available resources, and ethical considerations. A balanced approach that integrates both techniques, along with sustainable agricultural practices, can help address global food security challenges and mitigate the environmental impacts of agriculture.

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.”

The video "How CRISPR lets you edit DNA" by Andrea M. Henle explains the science behind the revolutionary gene-editing tool CRISPR-Cas9.

Key points covered:

• Genes as the blueprint of life: The video starts by establishing that every living organism is defined by its genes, which contain the instructions for building and maintaining an organism.

• CRISPR's origins: CRISPR was originally discovered in bacteria as a defense mechanism against viruses.

• Mechanism of CRISPR-Cas9: The video details how CRISPR-Cas9 works:

  • Guide RNA: A guide RNA molecule is designed to match a specific DNA sequence in the target gene.

  • Cas9 enzyme: The Cas9 enzyme, a type of protein, acts as "molecular scissors" that cut the DNA at the targeted location.

  • DNA repair: The cell's natural repair mechanisms try to fix the cut, which can be exploited to introduce changes in the DNA sequence.

• Applications of CRISPR: The video highlights the potential of CRISPR-Cas9 in various fields:

  • Medicine: Curing genetic diseases, developing new treatments for cancer and other illnesses.

  • Agriculture: Creating crops that are more resistant to pests, diseases, and drought.

  • Biotechnology: Developing new products and processes, such as biofuels and pharmaceuticals.

• Ethical Considerations: The video briefly touches upon the ethical concerns surrounding gene editing, particularly in the context of human embryos and germline editing, which could have lasting effects on future generations.

Overall, the video provides a concise and accessible explanation of CRISPR-Cas9, its mechanism of action, potential applications, and ethical considerations. It serves as an excellent introduction to this groundbreaking technology that has the potential to revolutionize various fields of science and medicine.

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!!!