lecture 23 Flashcards
how did complexity evolve/what could it have arose from?
its argued greater complexity arose from previous independent units
ex. cells, chromosomes, genetic code, sexual reproduction, eukaryotes, multicellularity, colonies all arose from the cooperation of previously independent units
how does fair mitosis and meiosis ensure allele cooperation?
one set of chromo fairly passed down from each parent is replicated in mitosis and ensures fair/even distribution of genetic material into each daughter cell
all cells created from zygote have equal rep of genetic material from each parent, so no competition based on what allele a person gets from what parent
how is cell competition prevented?
development and multicellularity, starting from single cell prevents competition among cell lineages, humans and other organism develop from single feritilized cell which goes through mitotic process and divides
all cells of individual are descended from same cell and due to mitosis all cells are equally descend/related/basically the same
what cld happen if an organism developed from 2 fertilized cells?
hypothetically if an organisms was developing form two fertilized cells there cld be a race b/w cell lineages competing w/ each other to get more resources, reproduce more, have more cellular descendant and this might be bad for the fitness/survival of the individual
how is competition b/w organelles prevented?
uniparental inheritance of organells (chloroplast, mitochondria) prvents competition within cells of diff organelle genomes, by always having organelles come from single parent, everything is the same, don’t need to worry comeptition b/w maternal and paternal mitochondria since all cells just have maternal mitochondria
what is meiotic drive?
cheating in meiosis/having unfair meiosis
one allele has higher transmission than other
what happens where there’s meiotic drive
if allele can enhance own transmission it will spread even if it reduces individual fitness
leads to excessive production of heterozygotes/homozygotes selection is acting against
meotic drive can rapidly eliminate alleles whic have higher individual fitness
what is drosophila segregation distorter locus?
if ss female mates w/ Sd male this will result in 95%-99% Ss offsprings which seems unrealistic if there’s fair representation of meiosis
females only contribute s, so something unusualy must be happening w/ males
in this case having a S prevents proper formation of s sperm, so only sperm males can create/donate have S allele
what is the consequence of meiotic drive scenarios like drosophila segregation distorter locus?
as a consequence of S alleles being transmitted more than it shld be, restorer alleles have evolved elsewhere in genome to silence S allele and restore transmission in male meiosis to 50/50 scenario
how do genomes remain cooperative?
for genomes to stay cooperative fair meiosis is nessecary, and when cheating alleles spread it creates strong selection on rest of genome to silence them/undo/counter their effects
what is overepliaction
overreplication happens when trasposable elements make copies of self and hop onto diff/insert into other chromos
gametes produced have overrepresentation of transposable element, results in overrepresentation in offsprings
what are transposable elements?
transposable elements are self replicating segments of dna, they’re independantly replicated dna elemants and can self copy, spread through genome, where they make copies of themselves and hop on diff chromosomes
transposons have severed connection b/w transmission and chromosome they’re on cuz can copy and put themselves onto other chromos, no longer dependant on chromo carrying themselves to next gen, can self copy to ensure they are transmitted
how common are transposons/selfish genetic elements?
most common dna in genome is this type of selfish, transposable genetic element
how is over overreplication stopped?
genomes dont overrun by transposition because by spreading rapidly transposons produce strong selection on rest of the organism to tamp down on transposition, lots of features of genomes/gene regulation have evolved to genome silence transposition, dna methylation, rna interference
what is transposition-selection balance?
transposition-selection balance is similar to balance of mutation and selection
transposition will favour spread of individual genes/elements which leads to more of these genetic elements
however if there are too many of these elements, or it lands in a crucial chromo/gene then whole organism dies and w/ it those tranposons also die
eventually selection will start to act against this, and so there will be balance of transposition increasing in spreadof transposons and selection tamping it down keeping it at an upper limit
