EE Lecture 13: The Evolution of Sex

Question 1

in how many angiosperms does obligate sexuality arise

Answer 1

~1%

Question 2

give some asexual animals

Answer 2

star fish
sea anemones
komodo dragons
ambystoma

Question 3

what sexuality is komodo dragon

Answer 3

asexual

Question 4

name an organism that has alternate sexual and asexual reproduction

Answer 4

Daphnia

Question 5

what is apomixis

Answer 5

the asexual formation of a seed from the maternal tissues of the ovule, avoiding the processes of meiosis

Question 6

what is vegetative propagation

Answer 6

asexual reproduction where only one plant involved and offspring is generally clone of parent

Question 7

what two methods of asexual reproduction exist in plants

Answer 7

apomixis

vegetative propagation

Question 8

what is the asexual formation of a seed called

Answer 8

apomixis

Question 9

what is the asexual reproduction of a plant, whereby it is genetically identical to the parent called

Answer 9

vegetative propagation

Question 10

what way does Daphnia reproduce

Answer 10

alternate sexual and asexual reproduction

eg.cyclical parthenogenesis

Question 11

which organism reproduces via cyclical parthenogenesis

Answer 11

Daphnia

Question 12

name the main types of asexual reproduction in animals

Answer 12

parthenogenesis
gynogenesis
hybridogenesis

Question 13

what animals does gynogenesis occur in

Answer 13

fish and ambhibians

Question 14

define parthenogenesis

Answer 14

development of an embryo from an unfertilized egg cell and is a component process of apomixis.

Question 15

what is gynogenesis

Answer 15

a sperm or pollen triggers the development of the egg cell into an embryo but makes no genetic contribution to the embryo

Question 16

what is hybridogenesis

Answer 16

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

Question 17

where are asexuals usually found in the tree of life

Answer 17

on the tips as recently derived from sexual ancestory

evolves fairly often in many plant,animal groups but are an evolnary dead end

Question 18

what are costs of sex

Answer 18

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

Question 19

what are benefits of sex

Answer 19

natural selection more efficient in sexuals
adaptation to changing enviro in sexuals is faster
eliminate deletrious mutations quickly

Question 20

why does sex allow faster adaptation to changing enviros

Answer 20

it permits genetic exchange between diverse lineages, promoting genetic variation

Question 21

discuss the evoln of salt tolerance in yeast

Answer 21

sexual wildtype strain evolved to adapt to high salt medium faster than asexual but asexualWILL catch up eventually due to REd Queen Hypothesis

Question 22

why is NS more efficient in sexuals

Answer 22

recombination “tries out” all different gene combos in pop - good ones spread, bad ones lost

Question 23

what is mullers ratchet

Answer 23

accumulation of deleterious mutations in asexuals

Question 24

in what orgs does mullers ratchet occur in

Answer 24

ONLY ASEXUALS

Question 25

why doesnt mullers ratchet occur in sexuals

Answer 25

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

Question 26

give reasons for why asexuals should speciate more than sexuals

Answer 26

time for conception not necessary - shorter life cycle
they should diversify into discreete independently evolving grps
dont need to evolve reproductive isolation

Question 27

give reasons for why speciation could be faster in SEXUALS rather than asexual

Answer 27

sexuals adapt faster
sexuals have no mullers ratchet to reduce fitness
sexuals have recombination
sexuals have more genetic variation

Question 28

how can you find out whether sexuals or asexuals speciate more quickly

Answer 28

use ancient asexuals: bdelloid rotifers

Question 29

what are bdelloid rotifers

Answer 29

ancient asexuals
no males
no meiosis
no sexual reproduction since origin

Question 30

how are bdelloid rotifers typified

Answer 30

by rotary apparatus and leech like locomotion

super abundant in damp habitats, moss, puddles

Question 31

what unusual process can bdelloid rotifers undergo

Answer 31

anhydrobiosis:live in harsh enviro and have dispersal in resting stage1

Question 32

discuss bdelloid genomes

Answer 32

no pattern of homologous chromosomes - there are homologous regions
lack retrotransposons
no males
lack some meiosis and spermatogenesis genes

Question 33

how long have bdelloid rotifers been asexual for `

Answer 33

~60 MYRS

Question 34

how were asexual bdelloid rotifer oocytes formed

Answer 34

through mitotic divisions - no chrom reduction/division/pairing

Question 35

how are bdelloid species distinguished

Answer 35

clear morphological differences: jaw size and shape

Question 36

have bdelloids speciated

Answer 36

yes

Question 37

why havent bdelloids gone extinct

Answer 37

special mechanism to compensate for lack of sex
well suited to harsh enviros
not really asexual, just discrete
they pick up foreign DNA

Question 38

what is most likely reason for why sex is so common

Answer 38

extinction rates of asexuals are quite high