Title: Chapter 20 suggested questions:
1Chapter 20 suggested questions 1, 6, 8
2Development
How does a single cell turn into a complex,
multicellular organism?
3Why 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
4Differential 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?
5Complete 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
6Complete Genome
Dolly
We now know it can work for differentiated
mammalian nuclei placed into enucleated mammalian
eggs.
7Differential 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.
8Development 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
9Maternal-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
10Maternal-Effect Genes
11Zygotic 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.
12Zygotic 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)
13Zygotic Genes Determine Segment Formation
14Development 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.
15Development and Evolution
Analogous homeotic genes determine the axial
development in both animals. Furthermore,
Drosophlia proteins can direct mouse axial
development and vis versa.
16Development and Evolution
Gene duplication has led to the expansion of the
Hox gene family.
17Development and Evolution
If all animals use the same basic proteins to
guide development, why do animals look so
different from one another?