lect 19 - eukaryotes and mitochondria Flashcards
(23 cards)
what are some key features of eukaryotic evolution ? (4 points)
euks are typically diploid
sexual reproduction and recombination
cellular and genomic complexity— that we dont see in proks
euks have wide range of population sizes (very small to very large)
how do population sizes of eukaryotes and prokaryotes relate to the forces of natural selection and genetic drift ?
on average, prokaryote population size is larger than eukaryotes
eukaryotes have a larger range of sizes from very small to very large due to having large multicellular organisms
in smaller population sizes such as in large multicellular eukaryotes, they are much more susceptible to genetic drift and forces like this. natural selection is less than in larger populations
natural selection affects on different population sizes
natural selection is stronger in large population sizes
small population sizes: less effective natural selection
horizontal gene transfer in euks vs proks
happening all the time in prokaryotes — more common and pervasive
less common and pervasive in eukaryotes — way more specific and smaller scale
example of horizontal gene transfer in eukaryotes
red aphids
carotenoids required for functions such as antioxidants, vision, and immune response
animals cant make carotenoids like plants can so have to get from diet
these aphids eat phloem — which doesnt have these
aphids have carotenoid biosynthesis genes that came from fungi — no other insect genes
what do eukaryotic genomes look like?
big
junk — non-coding DNA, pseudogenes etc
accumulates more junk here than other things
lots of variation in sizes
unlike prokaryotes, in euks size does NOT equal complexity
a difference of prokaryote genomes versus eukaryote genomes (complexity and size)
— C value paradox
when prokaryote genomes are bigger, they are more complex and vice versa — size related to complexity
eukaryotic genomes not related size and complexity — bigger doesnt equal more complex
example of euk genome size variation
Drosophila melanogaster
collected from the same place — huge variation in their genome size
most DNA in eukaryotes is _____
non-coding
most DNA in prokaryotes is _____
coding
how do spandrels of san marco relate to euk non-coding DNA ?
showing that the evolution to have these things doesnt always mean that it’s necessary. like having a nose for glasses or glasses for a nose — why do we have so much non-coding DNA ?
what is the human genome composed of ?
mostly transposable elements (jumping genes) 45% - which are good at making more of themselves (against mendelian)
— often duplicate the same genetic material
— can change genome size
they can be good or bad
— disrupt normal gene function causing diseases
why is the onion genome larger than our genome ?
lots of things that arent needed
euks have small population sizes — natural selection isnt as efficient at getting rid of things that arent needed
NUMTs
nuclear embedded mitochondrial DNA
whole genome sequences of mitochondrial genome into the nuclear genome
— after being embedded, not under evolutionary constraints seen in the mitochondria
most NUMTs are rare, but common NUMTs are small
pseudogenes become fixed on branch to humans — most common
—> fixed bc of chance events
what are some key features of mitochondrial evolution ? (5 points)
descended from bacteria
inherited through one parent (mostly maternal)
very different mutation rates (very high in animals) — higher mutation rates than nuclear DNA
no recombination — inherited and transmitted in one piece
neighbours matter
what are the consequences of no recombination ? (ex of the mitochondrial genome)
no recombination and small pop size = susceptible to chance events and deleterious mutations — mullers ratchet (accumulation of slightly deleterious mutations) — leading to an irreversible decline in fitness
mitochondrial defects during aging due to deletions and duplications
high mutation rates (in animals)
high levels of free oxygen radicals (mutagenic)
frequent replication in non-dividing cells — increased chance of error
missing some of the major pathways for DNA repair — doesnt mean dont have purifying selection, just at different scales and different risks
mitochondrial genomes used for DNA barcoding (marker in evolution) — relatively small and conserved
human mitochondrial diseases
Leber’s hereditary optic neuropathy (LHON) — most common cause of male adolescent blindness
Leigh syndrome (or subacute necrotizing encephalomyelopathy) — affects central nervous system
reduced sperm motility
due to deleterious mutations — (frequencies of deleterious mutations can reach as high as 5% in some populations)
problems associated with mitochondria
since no recombination and inherited thru only one parent (as a whole)
high mutation rates
muller’s ratchet — accumulation of slightly deleterious mutations
male adolescent blindness (Leber’s)
problems w central nervous system (Leigh)
reduced sperm motility (T mito haplogroup in humans) — leading to infertility in human males
fille du roy
associated w Leber’s hereditary optic neuropathy
french canadian study
founder effect — but introduced by female ancestor bc of maternal inheritance (shared female ancestor of 11/13 affected individuals)
filles du roy — sent single and orphan women to colonize bc had more men than women
this study took data of every individual from records in Nouvelle-France
— FOUND : 2 factors effected fitness - being male and having this certain haplotype — this haplotype did NOT have a negative effect on women
ONLY deleterious in males — neutral in females so not taken out by natural selection
“mothers curse” — mitochondria are passed thru females — only deleterious in males so not removed by natural selection
conflict between mitochondria and nuclear genomes
evolutionary interests of mito and nuclear genomes are not always the same — shows power of deep and ancient symbiosis
all a consequence of transmission — when exclusively passed thru one sex, might not be perfectly matched w the nuclear genome
example of selfish mitochondria
mitochondria that sterilizes males
— breaks the rules of mendelian inheritance
Cytoplasmic male sterility (CMS) — in mito, not nuclear genome
mostly common in plants
Cytoplasmic male sterility (CMS) and study
mitochondrial trait causes male flowers to be sterile
expressed and encoded in mito genome
very common in species of plants that produce both male and female flowers (maize, rice, cotton, wheat) - polymorphic
CMS used by crop breeders to prevent self-fertilization — so it puts more energy into making female flowers
co-evolution between mito sterility genes and nuclear restorer genes
— CLEAR EXAMPLE of conflict
STUDY: COX11
study about CMS
CMS in rice caused by WA352
interferes w conserved nuclear gene COX11
COX11 removes radical oxygen species
this interference kills developing pollen
conflict of having WA352 that is active in the mitochondrion — kills pollen by interacting w COX11
