Chapter 18 Flashcards
Development is ____________________________. The key to understanding development is to understand how ____________________________________ impact cell differentiation and specialization
the building of a multicellular organism, different patterns of gene expression
T or F: reverse genetics approach identified most of the genes involved in development
False, forward genetics did.
What are the three fundamentals of development?
(1) Cell differentiation
(2) Positional information (gradient model)
(3) Pattern formation (body-plan axes)
Explain Cell Differentiation
A single-celled zygote undergoes several mitoses, becoming a cluster of embryonic stem cells which eventually divide and differentiate
T or F: in adult animals, most cells have differentiated and are locked into that cell type but there are exceptions with pluripotent stem cells that can be differentiated into a limited number of cell types
True
Explain Positional Information
all cells have the potential to differentiate into the same fate but this differentiation can depend on the concentration of a morphogen along a gradient
Morphogens
substances whose presence in different concentrations determines developmental fates
How are morphogen gradients formed?
1) dividing cellular contents within cells
2) asymmetric cell divisions - daughter cells inherit distinct subsets of the factors present in the original cell
Explain Pattern Formation
the interacting events that organize differentiating cells to establish the body-plan axes: anterior-posterior, dorsal-ventral, left-right.
Organizers are cells…
that determine their neighbors identity and fate
Induction VS Inhibition
Induction: induces the neighboring cells to adopt a specific fate
Inhibition: prevents its neighbors from adopting a certain fate
In Drosophila larvae, what are the five classes of mutations that influence Drosophila development?
1) Coordinate Genes: defects affect an entire pole of larvae
2) Gap Genes: mutants are missing large, contiguous groups of segments
3) Pair-rule Genes: mutants are missing parts of adjacent segment pairs, in alternating patterns
4) Segment polarity Genes: defects affect patterning within each of the 14 segments
5) Homeotic (Hox) Genes: defects affect the identity of one or more segments
In Drosophila, there are two homeotic clusters on the third chromosome: the ______________ complex (3 genes) and ___________ complex (5 genes) - the order of theses genes reflects the positions along the anterior-posterior axis
Bithorax, Antennapedia
T or F: in drosophila larvae, segment-polarity genes activate gap gene expression patterns and they both determine expression patterns of pair-rule and coordinate genes - individual segments acquire their unique identities through Hox genes
False, segment-polarity and coordinate genes are switched.
How are human digits determined?
All tetrapod’s are characterized by five or fewer digits per set, with each digit having its own unique identity, specified by hox gene expressions
4 Mutations that Alter Digit Formation
1) Ectopic…
2) Mutations that…
3) Separation of…
4) Loss of…
(1) Ectopic expression of Hoxd genes can alter digit identity
(2) Mutations that expand or increase expression of Shh gene (upstream of Hoxd genes) result in formation of extra digits
(3) Separation of the limb bud into individual digits in humans requires programmed cell death between the digits
(4) Loss of limbs in snakes/cetaceans is due to alterations in Hox and/or Shh gene expression
T or F: roundworms are free-living transparent animals, adult males have roughly 1031 cells while adult hermaphrodites have roughly 959 cells, they have a lifespan of 2-3 weeks and a generation time of 3-4 days. They have five pairs of autosomes and one pair of sex chromosomes (Males: XO, Hermaphrodite: XX)
True
How does a roundworm’s vulva develop?
The vulva forms during the last larval stage, from six precursor cells (VPCS, P3 to P8) - 3 actually give rise to structures of the vulva itself (primary cell and sides on either side are secondary cells)
Lateral Inhibition
once a lin-3 signal is received by the primary cell, a second signal is sent that inhibits neighboring cells from becoming primary cells
Primary Cell Induction
the anchor cell has the lin-3 gene which encodes a small, secreted protein that acts as the signaling molecule for primary cell
Plants represent an independent event in multicellular evolution and the two major differences between animals and plants are…
1) animals have early separation of germ cells
2) plants can add new organs after maturity
Meristems
pluripotent cells in plants, there are root meristems and shoot meristems (leaf, axillary, and reproductive meristems)
How is plant flower development genetically controlled?
ABC Model
Arabidopsis thaliana is a model plant for genetics research, they are composed of 4 concentric whorls of organs:
sepals, petals, stamens, carpels.
For the ABC model, what does the A, B, and C genes encode for?
Sepals: A
Petals: A + B
Stamens: B + C
Carpels: C
Describe the 3 classes of mutations in Arabidopsis
A) carpels (1/4) & stamens (2/3)
B) carpels (3/4) & sepals (1/2)
C) sepals (1/4) & petals (2/3)
ABC genes act as ________________ and contain the homeotic ____________. These _____________ genes are not related to Hox genes in animals.
transcription factors, MADS box, MADS box
