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Title: Chapter 20 suggested questions:


1
Chapter 20 suggested questions 1, 6, 8
2
Development
How does a single cell turn into a complex,
multicellular organism?
3
Why Talk About Development in Genetics Class?
  • Different sets of genes are expressed in
    different cells.
  • The differentiated state attained by a
    specific cell type is determined by the genes
    that are actively transcribed in that cell.
  • Do not forget translational and
    postranslational control.
  • - a cell is determined the genes are expressed
  • - a cell is differentiated when the proteins
    are made

4
Differential Gene Expression
How do different cells, in different tissues
express only a small subset of all the possible
proteins that are encoded in the genome of an
organism?
Do all cells lose DNA in order to differentiate?
5
Complete Genome
Nuclei extracted from differentiated cells were
totipotent, or capable of giving rise to a
complete organism under certain conditions.
Worked well for differentiated amphibian nuclei
placed into enucleated amphibian eggs
6
Complete Genome
Dolly
We now know it can work for differentiated
mammalian nuclei placed into enucleated mammalian
eggs.
7
Differential Gene Expression
How do most cells, in different tissues, express
only a small subset of all the possible proteins
that are encoded in the genome of an organism?
It is a systematic stepwise process, allowing
different genes or combinations of genes to be
expressed at different times.
8
Development in Multicellular Eukaryotes
  • Determined by selective expression of
    specific gene sets in cells with equivalent
    genomes
  • Cytoplasmic inheritance of components by
    location of cells within the zygote influences
    development
  • Cell-Cell interaction controls cell fate
    during development

9
Maternal-Effect Genes
  • Gene products are deposited in the egg
    during oogenesis
  • Often distributed in a concentration
    gradient along the embryo
  • Mutations produce female sterility due to
    homozygous state
  • Encode transcription factors, receptors and
    other proteins
  • Control expression of zygotic genes

10
Maternal-Effect Genes
11
Zygotic Genes
  • Genes present in the developing embryo that
    are transcribed after fertilization
  • Maternal gene products regulate
    transcription of zygotic genes.


Bicoid stimulates expression of hunchback and
nanos inhibits it.
12
Zygotic Genes Determine Segment Formation
  • Classified on the basis of their mutant
    phenotypes
  • Gap genes delete a group of adjacent
    segments (Krüppel and knirps)
  • The pair rule genes effect every other
    segment (even-skipped, runt, hairy)
  • The segment polarity genes cause defects in
    homologous portions of each segment (hedgehog,
    armadillo, gooseberry, naked, disheveled)

13
Zygotic Genes Determine Segment Formation
14
Development and Evolution
Why study Drosophila develomental genetics?
Although the wings of a fly are vastly different
from those of a chicken, analogous genes are
expressed in similar regions of each developing
wing at similar stages of development.
15
Development and Evolution
Analogous homeotic genes determine the axial
development in both animals. Furthermore,
Drosophlia proteins can direct mouse axial
development and vis versa.
16
Development and Evolution
Gene duplication has led to the expansion of the
Hox gene family.
17
Development and Evolution
If all animals use the same basic proteins to
guide development, why do animals look so
different from one another?
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