A

BIOL 310 - Ch 22 Lecture Notes

  • cell determination

    • cells are committed to specific patterns of gene activity

    • cells restrict an embryonic cell’s developmental pathway

      • fate becomes more and more limited

      • branching tree

    • eg. human retina

  • cell differentiation

    • final step in cell specialization

    • the cell has a characteristic appearance and function

    • appears to be irreversible; committed to its fate

  • cell specialization

    • differential gene expression

    • causes difference among cell types

      • gene activation

      • gene repression

      • transcription factors

      • DNA binding protein

    • self-perpetuating and not easily reversible

  • Dolly — cloned sheep

    • cloned from somatic cells

    • all the genes were forced to an “undifferentiated state”

      • buffers and electroelution to change the cells to become undifferentiated & put those nuclei in an egg which was stimulated to divide meiotically

  • Drosophila development

    • fertilization

    • nuclear division

    • nuclear migration

    • cellular membrane growth

    • pole cell development

    • establish axis

    • segment number and orientation

    • identify each segment

  • polarity genes

    • maternal effect genes (mRNA is transcribed in the mother & put in egg)

      • anterior determinant

      • posterior determinant

      • bicoid & nanos — mRNA attaches to the the cytoskeleton of the egg (transcription factors)

        • gradient of biocoid protein diffusing from the front end & nanos diffusing from the rear end

        • distribution of protein; different relative amounts of each transcription factors results in slightly different patterns of gene expression and ultimately different character expression in those cells

      • distribution of mRNA during development

    • morphogen gradients

      • morphogens facilitate morphogenesis in the butterfly wing

      • visualization of this differentiation is evident based on the appearance of several spots on the wing where morphogens are released

        • depending on the concentration there are different colors expressed; ranges!!

    • segmentation genes

      • gap — split the body into three main regions: head, thorax & abdomen

      • pair rule — split those regions into segments

      • segment polarity — determine the front vs the rear for each of the segments

  • homeotic genes

    • alter how each segment develops; specify the identity of each segment during development

      • homeobox genes (HOX genes)

      • specify identity of each segment

      • act later in development — differentiation

    • 8 genes; 180 nucleotide “boxes” are similar in sequence

    • eg bithorax & antennapedia

  • Hox gene clusters

  • Hox genes in vertebrates

    • shape the number & appearance of body segments (repeated structures) along axis

    • differential hox-gene expression (when and where) regulates differently between vertebrates & invertebrates

    • number and types of vertebrae

      • chicken: Hoxc-6 = 7 ribs

      • snake: Hoxc-6 = many ribs

  • conserved developmental genetics

    • similar development controls across taxa

    • mechanism evolved early