EE Lecture 13: The Evolution of Sex Flashcards
in how many angiosperms does obligate sexuality arise
~1%
give some asexual animals
star fish
sea anemones
komodo dragons
ambystoma
what sexuality is komodo dragon
asexual
name an organism that has alternate sexual and asexual reproduction
Daphnia
what is apomixis
the asexual formation of a seed from the maternal tissues of the ovule, avoiding the processes of meiosis
what is vegetative propagation
asexual reproduction where only one plant involved and offspring is generally clone of parent
what two methods of asexual reproduction exist in plants
apomixis
vegetative propagation
what is the asexual formation of a seed called
apomixis
what is the asexual reproduction of a plant, whereby it is genetically identical to the parent called
vegetative propagation
what way does Daphnia reproduce
alternate sexual and asexual reproduction
eg.cyclical parthenogenesis
which organism reproduces via cyclical parthenogenesis
Daphnia
name the main types of asexual reproduction in animals
parthenogenesis
gynogenesis
hybridogenesis
what animals does gynogenesis occur in
fish and ambhibians
define parthenogenesis
development of an embryo from an unfertilized egg cell and is a component process of apomixis.
what is gynogenesis
a sperm or pollen triggers the development of the egg cell into an embryo but makes no genetic contribution to the embryo
what is hybridogenesis
half the genome is passed intact to the next generation, while the other half is discarded. It occurs in some animals that are hybrids between species
where are asexuals usually found in the tree of life
on the tips as recently derived from sexual ancestory
evolves fairly often in many plant,animal groups but are an evolnary dead end
what are costs of sex
2fold cost of sex - sexual female only related by half to offspring, this halves next gen as wellq
Cant reproduce alone, cost of finding a mate
costrly traits needed to gain access to mates
increase risk of disease
what are benefits of sex
natural selection more efficient in sexuals
adaptation to changing enviro in sexuals is faster
eliminate deletrious mutations quickly
why does sex allow faster adaptation to changing enviros
it permits genetic exchange between diverse lineages, promoting genetic variation
discuss the evoln of salt tolerance in yeast
sexual wildtype strain evolved to adapt to high salt medium faster than asexual but asexualWILL catch up eventually due to REd Queen Hypothesis
why is NS more efficient in sexuals
recombination “tries out” all different gene combos in pop - good ones spread, bad ones lost
what is mullers ratchet
accumulation of deleterious mutations in asexuals
in what orgs does mullers ratchet occur in
ONLY ASEXUALS
why doesnt mullers ratchet occur in sexuals
because sexuals can restore optimum genotype via recomination and only way asexuals can restore optimal genotype is by back mutation which is likely to be rare
give reasons for why asexuals should speciate more than sexuals
time for conception not necessary - shorter life cycle
they should diversify into discreete independently evolving grps
dont need to evolve reproductive isolation
give reasons for why speciation could be faster in SEXUALS rather than asexual
sexuals adapt faster
sexuals have no mullers ratchet to reduce fitness
sexuals have recombination
sexuals have more genetic variation
how can you find out whether sexuals or asexuals speciate more quickly
use ancient asexuals: bdelloid rotifers
what are bdelloid rotifers
ancient asexuals
no males
no meiosis
no sexual reproduction since origin
how are bdelloid rotifers typified
by rotary apparatus and leech like locomotion
super abundant in damp habitats, moss, puddles
what unusual process can bdelloid rotifers undergo
anhydrobiosis:live in harsh enviro and have dispersal in resting stage1
discuss bdelloid genomes
no pattern of homologous chromosomes - there are homologous regions
lack retrotransposons
no males
lack some meiosis and spermatogenesis genes
how long have bdelloid rotifers been asexual for `
~60 MYRS
how were asexual bdelloid rotifer oocytes formed
through mitotic divisions - no chrom reduction/division/pairing
how are bdelloid species distinguished
clear morphological differences: jaw size and shape
have bdelloids speciated
yes
why havent bdelloids gone extinct
special mechanism to compensate for lack of sex
well suited to harsh enviros
not really asexual, just discrete
they pick up foreign DNA
what is most likely reason for why sex is so common
extinction rates of asexuals are quite high
