BIO220Winter2025_Lecture3_1slideperpage

Beyond BIO: Optional Activities for BIO220 Students


  • What’s Beyond BIO?Optional events offered to BIO220 students aimed at being fun and informative.

    • More details available on Quercus under Modules -> Beyond BIO.

Upcoming Events:

  • BIO220 Social!

    • Date: Tuesday, January 14th at 2:10 PM

    • Location: Room RW 010 in Ramsay Wright

    • Description: Start the term with snacks and trivia. Meet classmates and enjoy refreshments. Everyone is welcome!

  • Birds & Wildlife of Toronto

    • Date: Thursday, January 23rd from 11:10 AM – 12:00 PM

    • Location: RW 432

    • Description: Learn about Toronto’s local wildlife, the best nature viewing spots, and become a naturalist. Refreshments and snacks will be provided.

Genetic Diversity in Agricultural Systems

  • Introduction:

    • The world possesses around 50,000 edible plants with only 3 species (rice, maize, wheat) accounting for 60% of food energy intake by humans.

    • Typically, only a few genotypes are cultivated, though abundant genetic variation exists in wild ancestors.

Crop Domestication and Its Effects

  • Bottlenecks:

    • Only a tiny subset of wild populations is chosen for domestication, leading to a severe genetic bottleneck.

    • Strong artificial selection occurs, favoring traits beneficial for agriculture:

      • Germination timing

      • Seed size

      • Nutritional content

Consequences of Domestication:

  • Reduced Genetic Variation:

    • How to measure:

      • H: Average frequency of heterozygous individuals per gene locus.

      • P: Proportion of gene loci that are polymorphic.

      • π: Average number of nucleotide differences per site among randomly sampled nucleotides.

    • Review relevant slides from BIO120 for understanding genetic variation maintenance.

Importance of Genetic Variation

  • Why We Care About Genetic Variation in Crops:

    1. Provides insights into past artificial selection and traits favored by ancestors.

    2. Aids in pest and pathogen management strategies.

    3. Facilitates future improvements of crops without reliance on genetic engineering.

Case Study: Maize Domestication

  • History:

    • Maize domesticated from teosinte between 10,000 to 5,000 years ago through artificial selection prior to genetic discoveries.

  • Genetic Diversity Comparison:

    • Domestication led to notable loss of variation between teosinte and maize.

    • Studies indicate a 43% reduction in variation due to artificial selection and bottlenecks.

Distinguishing Genetic Factors

  • Effective Population Size (Ne):

    • Defined as the size of an idealized population exhibiting the same genetic drift and allele frequencies as the observed population.

  • Census Size (N):

    • Total number of adults in a population where Ne << N.

    • Ne is critical for evolutionary analysis, reflecting actual breeding individuals.

Genetic Variation Measures

  • Consequences of Variation in Progeny:

    • Variation in progeny numbers leads to stochastic differences in contribution from individuals.

    • Factors influencing Ne include unequal sex ratios, overlapping generations, and population size fluctuations.

Bottlenecks and Selection Dynamics

  • Bottleneck Effects on Genetic Variation:

    • A bottleneck affects the entire genome; all loci are impacted by Ne.

  • Selection Loci:

    • Selected loci experience even greater reductions in Ne compared to the overall genome.

Key Insights on Domestication

  • The reduction in Ne has genome-wide impacts due purely to demographic bottlenecks, while artificial selection further decreases Ne for specific loci.

Implications from Historical Case Studies

  • Irish Potato Famine (1845-1852):

    • Catastrophic loss of life corresponded with potato cultivation's reliance on limited genotypes, leading to vulnerability against phytopathogens.

  • Potato Blight:

    • Introduced by Phytophthora infestans, leading to widespread potato rot and subsequent starvation.

Sociocultural and Biological Implications

  • Monocultures undermine genetic variation, resulting in increased susceptibility to disease and crises in agriculture.

  • Lessons Learned:

    • Highlighting the need for diverse planting strategies to mitigate risks associated with genetic uniformity.

Future Considerations in Agriculture

  • Artificial Selection:

    • Despite genetic reductions seen in crops like maize, questions remain regarding the future viability of artificial selection in improving crop yields.

  • Genetic Variation Challenges:

    • Addressing the specific genetic limitations in crops that do not easily crossbreed or reproduce effectively.

Recap Takeaways

  • Understanding genetic variation aids in revealing past selections and improvement mechanisms in agriculture.

  • Ethical questions surrounding GMOs and their potential role in sustainable agricultural practices.