Lecture 20/21 Flashcards
transposable elements are _______ in large genomes
transposable elements are ABUNDANT in large genomes
are genomes large because they have TE or do genomes have TE because they are large?
how do they know?
genomes are large because they have TE
compare closely related plants –> ones with larger genome has more TE
Where are transposable elements found? what does this indicate about how they affect genes?
in INTRONS/intergenic regions, therefore not disrupting genes very much
why are transposable elements found mainly in introns?
would be lethal if they are in exon –> the TE are not targeting themselves to introns, just being negatively selected when inserted into exons
when can introns insert into genes? consequence?
1/600 spontaneous mutations causing human disease are due to transposition of TE in gene –> not persistent over time, just appear in an individual
3 ways that TE affect genome
- insertion in gene induces LOF
- inserion disrupts splice potential
- TE mobility destabilizes genome to cause cancer
why are TE helpful?
allow for phenotypic novelty and adaptive change
describe the dysgenic cross of drosophila
female lab strain X male wild-caught strain
F1 are normal but germline cells don’t develop so no F2 can develop
why do the germline cells not develop in dysgenic cross?
mobile P element in male wild-caught strain causes genome instability leading to mutation, abnormal chromosomes, and non-disjunction
describe the reciprocal cross of drosophila
male lab strain X female wild-caught
F1 normal, germline cells normal, F2 normal
what strain carries the P element?
wild-caught
what can we conclude from the fact that the germ cells are normal despite the wild-caught strain carrying the P element?
there must be a mechanism in FEMALE wild-caught that blocks P element mobility and preserves genome integrity
what is the result of male wild-caught X female wild-caught? why?
everything normal –> bc female wild-caught is present
describe the TE studied in C. elegans
Tc1 is class 2 TE that autonomously encodes transposases
why do we want to use Tc1 to study TE mobility?
Tc1 elements only transpose in somatic cells, not germline cells –> therefore must be ‘silencing machinery’ that represses Tc1 mobility
why is it important that the silencing machinery is encoded by genes?
we can KO genes and perform a genetic screen
describe the genetic screen performed in C. elegans
randomly KO genes
- if the gene silences mobility: the KO will make Tc1 jump out of Unc22 and worm will be smooth-gliding
- if the gene is not involved in silencing: Tc1 will stay in Unc22 and worm will be twitching/uncoordinated
what allows us to see effects of Tc1 in progeny?
Tc1 mobility is affected in germline cells, so the mutations are affecting germline cells and we can see effects in progeny