EB11 (part 2) Flashcards
(20 cards)
what is the rate of divergence comparitively in the three degenerative degrees in humans and rodents
what does this indicate
- zero fold lowest rate of change divergence - indicate purifying selecction
- 4 fold: fasterest rate of change
- 2 fold = average rate of change
what kind of divergence do introns show in humans and rodents
similar to 4 fold - fast divergence
** however sometimes introns express control sites so may have lower mutation rate
what kind of divergence do 3’ flanking sites show in humans and rodents
similar to 4-fold = fast divergence
what kind of divergence do 5’ flanking sites show in humans and rodents
similar to 3 fold divergence
as often contain regions important for expression of genes
what kind of divergence do psuedogenes show in humans and rodents
similar to 4 fold - nearly neutral so mutate quickly
what is an abalone
large marine mollusc releasing sperm into the sea
how do abalone sperm and egg differ in selection preferences
male: many sperm competing for access to egg, selects fastest sperm to fuse
female: one egg to accept the best sperm and avoid polyspermy, which is fatal to the embryo= selects for changes in egg receptor to achieve ‘poor fit’ to sperm surface and slow down fusion.
what is lysin
a membrane bound protein that binds to the eggs envelope and unravels it thus allowing fertilisation
* regulates species specific interaction between sperm and egg
why in lysin interesting in abalones
as it shows divergence across the 25 abalone species
what is the neutral expectation for dN/dS
1
expect to evolve at equal rates if evolvign neutrally
what is the dN/dS for abalone lysin in different parts
~ 3 at the periphery of the molecule which interacts with the egg membrane - shows fast divergence, positive selection - coevo chase between male and female gamete receptors
~ 0.09 at part forming the core of the molecule (more constrained to maintain overall structure) showing slow divergence. = purifying selection
what is VDE
an intein selfish element with homing endonuclease inside the host VMA gene in yeast
what does intein mean
it resides and is hosted by hosts genes: if reside inside an important gene it reduces the risk of losing its home to selection, especially if HEG is deleterious
how does HEG enzyme work
HEG enzyme recognises site in homologue allele cuts (ds break); cell uses homologue containing HEG to repair break, copying HEG into non-HEG homologue, thus doubling the no. of HEG copies in the genome
what is HEG an example of
super mendalian inheritance
converts +/- to +/+ homozygote
how were VDE sites in yeast analysed
alignment of VDE sequences from 14 species of Saccharomyces
sites tested by site directed mutagenesis to identify sites important for function.
what did analysis of VDE sites show
sites critical for splicing function are 100% invariant - self splicing intron
non- critical sites show much higher degrees of variability. e.g. sites critical for endonuclease lack of conservation, indicates various state of degneration of endonuclease formation
what sites tend to be highly conserved
functionally important sites
what can conserved sites in an alignment be used to deduce
functionality of sites, e.g. find control sites in non-coding regions etc.
what is the neutral expectation for dN/dS and pN/pS
that dN/dS = pN/pS = 1
