Texas Tech University

Lewis Irving Held

Associate Professor
Developmental Genetics

Email: See TTU Directory

Phone: (806) 834-3283

  • Ph.D., Molecular Biology, University of California Berkeley, 1977.
  • B.S., Life Sciences, Massachusetts Institute of  Technology, 1973.

Teaching Awards

  • President's Excellence in Teaching Medal, TTU, 1995.
  • Professing Excellence Award, University Student Housing, 2010.
  • Professing Excellence Award, University Student Housing, 2016.
  • Apple Polishing Award, TTU Mortar Board, Senior Honors, 2020.
  • Apple Polishing Award, TTU Mortar Board, Senior Honors, 2021.
  • Apple Polishing Award, TTU Mortar Board, Senior Honors, 2023.

Book Awards

  • 2nd Place Medal, TTU University-wide Book Competition, 2004.
  • 2nd Place Medal, TTU University-wide Book Competition, 2011.
  • 3rd Place Medal, TTU University-wide Book Competition, 2016.
  • 3rd Place Medal, TTU University-wide Book Competition, 2019.
  • 2nd Place Medal, TTU University-wide Book Competition, 2023.
Dr. Held

Web Links:


Wall Street Journal
interviews Prof. Held about Darwinian evolution

Cambridge Univ. Press interviews Prof. Held about Darwin's legacy

Daily Toreador interviews Prof. Held about life & a fly joint mutation


For student use only (BIOL 3302):  Best Podcast Ever (3 hours); Making Robotic Embryos; CRISPR as a DNA-editing tool; StemCells1; StemCells2; StemCells&Cancer; Organoids1Organoids2; Organoids3; Organoids can repair the retina!;RegrowArms?; MorphogenGradients; Morphogen Case Study: Axes of the Inner Ear; Source-SinkGradients; HedgehogPathway; MovieTranscript.
Human embryology lectures:  L21, L22, L23, L24, L25, and L26.

Click here (searchable) or here (full text) to access the 6th Edition of Gilbert's textbook Developmental Biology.
Click here to search for other (free) digital copies of science textbooks.

For student use only (BIOL 4110):  EvoDevoVideo1; EvoDevoVideo2; EvoDevoSlideshow; EvoDevo1EvoDevo2EvoDevo3EvoDevo4; FlyArt.

For student use only (BIOL 1403):  EvolutionSlideshow.

"Playgrounds" for Pre-medical Student Explorers

Cornucopia of CONCEPTUAL FRAMEWORKS (Medical).
NCBI:   The National Center for Biotechnology Information.
PubMed:  Database of (clinically-related) published articles.
OMIM:  Database of genetically caused diseases in humans.
The future of medicine:
  Overview, Epidemics, Immunity, Autoimmunity, CRISPR, Paralysis, Aging, Microbiome, Pollutants, Heart, Cancer, Stem Cells. = Survey of emerging technologies.


Flies ≈ humans!
OrganSystems; Vision; WhyFlies?Video1(Basic); WhyFlies?Video2(Advanced); WhyFlies1?WhyFlies2?WhyFlies3?WhyFlies4?; WhyFlies5?; WhyFlies6?; WhyFlies7?; WhyFlies8?; WhyFlies9?; WhyFlies10?; WhyFlies11?; WhyFlies12?; WhyFlies13?; WhyFlies14?; FlyWorld1; Links-to-Literature.

"Wonderlands" of Fly Genes InteractiveFly; FunWithFlies; Twitter; Nobel Prizes.

Nobel Prize to 3 Fly Guys (2017): Awarded for basic research on circadian rhythms in fruit flies to Jeff Hall, Michael Rosbash, and Michael Young.

Whimsical musical parodiesEvo-devo (lyrics); Biochemistry; Science appreciation; catalog of Tim Blais videos.

Seminar "Hamlet on the Fly": Slide presentation; Slide comments.

Research Interests

Research in my lab has focused on pattern formation: how do cells construct anatomy? The model system we have used is the leg of the fruit fly and its exquisitely intricate patterns of bristles. Over the years we have probed how various signaling pathways (TGF-beta, Wnt, and EGFR) establish the axes, boundaries, and coordinates of the leg landscape.  Recently we solved (at least partially) an intriguing riddle in evolutionary developmental (evo-devo) biology: how did the 1st pair of legs become different from the 2nd pair in terms of its sex comb (on the male tarsus) and its transverse rows (on the tarsi and tibiae of both sexes)?  By using RNAi to suppress gene function at different stages we found that Scr--a master gene in the Hox complex--causes transverse row bristles to be yellow and bractless by direct intervention, whereas its other effects appear to be mediated indirectly by as-yet unidentified circuits.  Some of those circuits appear to depend upon Ubx--another  gene in the Hox complex--so we are now examining Ubx's role by a similar approach:  using the RNAi strategy to downregulate (or a Gal4 technique to upregulate) Ubx and/or Scr gene activity separately or simultaneously.  Surprisingly, perhaps, our research on Hox genes may eventually have medical/clinical applications for human birth defects because the very same Hox orthologs are used to establish "area codes" in the axial skeleton and nervous system of Homo sapiens!  Indeed, another facet of our work pertains to the exciting new field of "evo-devo", which seeks to understand the cellular mechanisms of embryogenesis in terms of genetic modifications by evolution in the genomes of flies and humans over the 600 million years since our two lineages diverged in the bilaterian family tree.  My book Deep Homology? (see below) explores this subject in detail.

Selected Publications

Department of Biological Sciences

  • Address

    Department of Biological Sciences, Texas Tech University, Box 43131 Lubbock, TX 79409
  • Phone

  • Email