lecture 17- evo devo Flashcards
deep homology
the exchangeability of the pox-6 mouse and eyeless (drosophila) genes between insects and vertebrates, implying conservation of ancient ancestral function
when is diversity established?:
during embryogenesis (in early embryogenesis, most vertebrates look very similar
totipotent
has the potential to develop into any cell type
determination
cell cannot determine it’s fate
how many different cell types are there
200
is determination reprogramming possible
yes
life cycle of a fruit fly
genetic control of development
complementation test
complementation test, also called cis-trans test, in genetics, test for determining whether two mutations associated with a specific phenotype represent two different forms of the same gene (alleles) or are variations of two different genes. The complementation test is relevant for recessive traits (traits normally not present in the phenotype due to masking by a dominant allele). In instances when two parent organisms each carry two mutant genes in a homozygous recessive state, causing the recessive trait to be expressed, the complementation test can determine whether the recessive trait will be expressed in the next generation
egg polarity genes
establishment of main body axes (dorsal, ventral, rostral, caudal)
segmentation genes
control the differentiation of the embryo into individual segments (determines the number and polarity of segments)
segment identity
establish the identity of each segment (like this part needs, wings, this part needs legs, this part needs genitals)
morphogens
proteins that vary in concentration and elicit different developmental responses at different concentrations
egg polarity genes: dorsal ventral axis
egg polarity genes: anterior-posterior
gradients
differential levels of these protein results in differential activation of downstream genes (like hunchback), important for anterior-posterior ends of the embryo
segmentation genes 1: gap genes
The gap genes are
responsible for defining the general regions of the embryo – specific gap
genes will be expressed in different sets of segments to differentiate the
thoracic segments from the abdominal segments, etc
segmentation genes 1: pair-rule genes
Each pair-rule gene is expressed in every other segment of the body, and together they control development of pairs of segments. Finally, within each segment
segmentation genes 1: segment polarity genes
guide the development of
individual segments, and ensure that they are organized appropriately
homeotic mutation
one part of the body is transformed to resemble another
hox genes are?
segment identity gene; mutations in these cause homeotic transformations
hox genes are transcription factors that control the expression of other genes to determine anterior-posterior segment identity, corresponding to their order on chromosomes
show similarity among very divergent organisms so they must be ancient
genetics of pelvic spine: qtl mapping
genetics of pelvic spine: pitx 1
reporter assays
used to identify activator/repressor binding sites upstream or downstream of the gene of interest, determines where and when and how much the regulatory element drives gfp expression
convergent evolution
similar traits evolving independently in different species
convergent evolution
similar traits evolving independently in different species
embryogenesis
process in which the foundation of an animal’s
form is established
saturation mutagenesis
by exposing males to a
mutagenic chemical that resulted in their sperm acquiring mutations
syncytium
In Drosophila,
early development is characterized by very rapid division of the nuclei,
without division of the cytoplasm. In a very short period of time, the egg
becomes a syncytium, essentially a bag containing hundreds of nuclei
that share a common cytoplasm. Those nuclei move out to the periphery
of the embryo so that they are aligned along the surface of the embryo,
at which point they become enclosed by cell membrane. The cells then
begin to express different genes, depending on where they are in the
embryo. In other words, they begin to differentiate themselves from one
another. From this point forward, these cells are no longer all the same.
maternal effect genes
The mRNA for the genes that regulate the initial steps of
differentiation are actually provided by the mother via the egg (i.e.,
maternal effect genes from Lecture 10). These are known as egg polarity
genes, and they establish the major body axes of the animal –
distinguishing anterior (head) from posterior (tail), and dorsal (back) from
ventral (belly). Some of these genes encode morphogens. Morphogens
are found at different concentrations along one of the body axes, and
act on cell differentiation in a concentration-dependent manner. For
example, a morphogen might activate expression of certain genes when
it is found at high concentrations, while activating other genes when it is
found at intermediate or low concentrations
Bicoid
egg polarity gene; Bicoid mRNA is found only in the very anterior-most
tip of the embryo, where its mRNA is anchored in the cell membrane.
When bicoid mRNA is translated, it forms a gradient of Bicoid protein,
which is highest at the anterior end (where the mRNA is localized). Bicoid
protein activates expression of a second gene, hunchback, which is
important for head development
Nanos
egg polarity gene; Nanos mRNA is found only in the posterior of the embryo, and when it is translated it forms a gradient of
Nanos protein, with the highest concentration at the posterior end. Nanos represses translation of hunchback, contributing to its expression only in the anterior of the embryo and helping to establish the head position. At the same time, Nanos promotes tail-making in the posterior. Between Dorsal, Bicoid, Nanos, and related proteins, the egg polarity genes use multiple morphogen gradients to establish the embryonic body axes, and generate a 3-D map of the embryo
transcription factors
a type of protein that binds DNA and
thereby regulates the expression of many downstream genes, turning
expression up or down
cis-regulatory elements
transcription-factor binding sites
The plant “toolkit” genes that are responsible for floral patterning are referred to as
ABC genes
In Arabidopsis flowers, the structures are organized into four
concentric rings, or whorls. Moving out from the middle of the flower are
whorls where different floral organs – carpels, stamens, petals, and sepals – form. Overlapping expression of three sets of genes (simply named: A, B, and C genes) determines which organ will form in each whorl.
A-genes are expressed in the two outermost whorls; C-genes are expressed in the two innermost whorls; B-genes are expressed in the two intermediate whorls. Thus, each whorl expresses a unique combination of ABC gene expression, which determines which type of organ is produced. In the outermost whorl, only A-genes are expressed, and sepals form. In the second whorl in, both A- and B-genes are expressed, causing petal formation. In the third whorl, B- and C-genes are expressed, causing stamens to form, and in the innermost whorl only C-genes are expressed, and carpels form there. Like with Hox genes, flower structures (in this case whorl identity rather than body segment identity) are determined by the
combinatorial expression patterns of ABC genes, and mutations in the
ABC genes cause homeotic transformations in flowers. For example,
plants that have a mutation in a B-class gene will produce only sepals in
the two outermost whorls, and only carpels in the two innermost whorls,
because each whorl will express only A- or C-class genes
