BIOL_2102-1023-Growth_and_Development

Growth and Development Notes

1. Overview of Growth and Development

  • Lecture 23 covers principles of growth and development in biology.

  • Focus on plant and animal development, highlighting evolutionary developmental biology (evo-devo).

2. Recap of Previous Material

A. Asexual and Sexual Reproduction

  • Asexual Reproduction:

    • Found in multicellular organisms.

    • Advantages: Simplicity, no need for mates.

    • Disadvantages: Less genetic diversity.

  • Sexual Reproduction:

    • Involves gamete formation (sperm and eggs).

    • Advantages: Genetic variation, adaptability.

    • Disadvantages: Requires more energy and time.

B. Evolution of Gamete Specialization

  • Variation in sexual reproduction.

  • Various sex determination systems.

C. Structural Support in Plants

  • Discussed previously (Lecture 09) with references to Darwin.

3. New Material Overview

  • Key topics include:

    • Plant growth and development.

    • Animal development.

    • Concepts in evolutionary developmental biology.

4. Plant Growth & Development

A. Primary Growth

  • Occurs in Apical Meristems:

    • Responsible for lengthening roots and shoots.

  • Zones in Primary Growth:

    • Zone of Elongation: cells elongate.

    • Root Cap: protects root tip.

    • Axillary Buds: potential for branching.

    • Leaf Primordia: develop into leaves.

B. Secondary Growth

  • Occurs in Lateral Meristems:

    • Increases plant circumference.

  • Vascular Cambium: adds secondary xylem and phloem.

    • Xylem grows faster than phloem.

  • Cork Cambium: produces cork cells on lateral sides.

C. Plant Growth Regulators (Hormones)

  • Auxin: promotes cell elongation and apical dominance.

  • Cytokinins: stimulate axillary bud growth.

  • Gibberellins: influence stem elongation, fruit growth.

  • Abscisic Acid: inhibits growth, induces seed dormancy.

  • Ethylene: regulates fruit ripening and leaf abscission.

D. Angiosperm Development

  • Gametophyte Development:

    • Female gametophyte (embryo sac) in each ovule (includes egg).

    • Male gametophyte develops in pollen grains (produces sperm).

  • Pollination: pollen transferred to stigma.

  • Double Fertilization:

    • One sperm fertilizes egg (2n zygote).

    • Other sperm fertilizes the central cell (forms endosperm).

  • Seed Development: ovule develops into seed, germinating into mature sporophyte.

E. Monocots vs. Eudicots

  • Monocots: single cotyledon.

  • Eudicots: two cotyledons.

  • Differences in embryonic development.

5. Animal Development

A. Fertilization

  • Sperm and egg fusion, species-specific surface recognition.

  • Changes in egg surface prevent polyspermy.

B. Cleavage

  • Series of mitotic divisions leads to the blastula (hollow ball of cells).

C. Gastrulation

  • Rearrangement of cells leads to the gastrula with layers of tissue.

  • First opening becomes the blastopore.

D. Organogenesis

  • Formation of rudimentary organs from germ layers.

  • Cells differentiate based on their fates.

E. Developmental Pathways

  • Protostomes vs. Deuterostomes:

    • Protostomes: mouth forms from blastopore.

    • Deuterostomes: anus forms from blastopore.

  • Diploblasts: have two germ layers (ectoderm, endoderm).

  • Triploblasts: have three germ layers (ectoderm, mesoderm, endoderm).

6. Evolutionary Developmental Biology (Evo-Devo)

A. Key Concepts

  • Heterochrony: changes in timing of developmental events.

    • Can lead to Paedomorphosis: retention of juvenile traits in adults.

  • Homeotic Genes: master regulatory genes for body organization.

    • Changes in Hox Genes can lead to significant morphological variations.

B. Metamerism and Tagmatization

  • Metamerism: body plans with repeated segments.

  • Tagmatization: specialized groupings of segments.

  • Hox gene regulation believed to contribute to diverse arthropod morphologies.

7. Case Study: Amphibian Limb Malformations

  • Causes and Impact:

    • Reports of malformations caused by chemical contaminants and parasites.

  • Ribeiroia ondatrae: trematode that affects limb development in amphibians.

    • Life cycle involves snails, larvae, and hosts (birds).

8. Study Reviews and Further Exploration

A. Study Review Questions

  • Differences in primary vs. secondary growth.

  • Functions of various plant structures (e.g., root cap, leaf primordia).

  • Developmental stages in animals and classifications (diploblasts, triploblasts).

B. Recommended Courses and Labs

  • Explore related topics in other biology courses at UNM.