lecture 14

Question 1

Sexual reproduction

Answer 1

characteristic of eukaryotes, and involves reproduction with meiosis and syngamy (fusion of gametes)

Question 2

Sexual reproduction results in new genotypes due to…

Answer 2

• independent assortment of chromosomes
• crossing over

Question 3

Sex in bacteria & viruses refers to what?

Answer 3

exchange of DNA
how we define sex

Question 4

Parthenogenetic (asexual) reproduction

Answer 4

“virgin birth”
not requiring exchange and mating with, with other individuals and fusion of gametes,
Has evolved in dependently many times and in many different ways

Question 5

facultative parthenogenesis

Answer 5

not always parthenogenetic/asexual
able to do both

Question 6

obligate parthenogenesis

Answer 6

always parthenogenetic/asexual

Question 7

Example: Amazon mollies (Poecilia formosa)

Answer 7

reproduce parthenogenetically, but require sperm from males of closely-related species to trigger development
females product asexual clones of eachother but need male sperm to trigger the development

Question 8

parthenogens are…

Answer 8

highly successful and abundant (and many pests, weeds, invasives)

Question 9

Case study: A high incidence of parthenogenesis
in agricultural pests

Answer 9

Wanted to count for every different family of insects, what percent of species are Parthenon genetic and then of every of every
pest species in that family, what percent are Parthenon genetic

Question 10

Case study: A high incidence of parthenogenesis
in agricultural pests

Figure

Answer 10

• each data point is a different family of insects from N. America
  
  • for one data point (look at graph): ~25% of the species in this family are parthenogens, but 80% of the species in this family that are pests are parthenogens

Question 11

Case study: A high incidence of parthenogenesis
in agricultural pests
results

Answer 11

if parthenogenesis is as frequent in pest species as in non- pest species, then a straight line with a slope of 1 is expected
* but instead we see all the families of different insects are way above the one to one to the left so they are over represented
* A higher percentage of them are of the ones that are pests-> A higher percentage of Parthenon genetic

Question 12

Even though parthenogenetic lineages are found across the tree of life, they are long-lived/short-lived over evolutionary time scales

Answer 12

short-lived
they are found on the tips of evolutionary trees

Question 13

Parthenogenesis is self-destructive for scaled reptiles MO Moreira, C Fonseca, D Rojas (2021) Biology Letters 17, 20210006

Answer 13

• scaled reptiles (Squamata) are the only vertebrates that repeatedly evolved parthenogenesis (39 described true parthenogens)
• performed a phylogenetic analysis and mapped mode of reproduction on the tree

Question 14

Results of MO Moreira, C Fonseca, D Rojas experiment

Answer 14

asexual reproduction parthenogenesis on the phylogenetic tree
on the tips, always evolved and arising but never last

why?
they tend to go extinict faster than sexual reproducing ones

Question 15

What are the benefits of parthenogenetic (asexual) reproduction?

Answer 15

what prof said:
- faster rate of growth (two fold cost of sex
- reproductive assurance
- no need to invest in expensive traits involved in sexual reproduction
- avoid STIs and other risks and costs of mating
- preserves successful genotypes

Question 16

The two-fold cost of sex

Answer 16

• If a sexually-reproducing female has 50% sons, then half of her resources have gone into offspring that can’t bear any offspring themselves!
• An asexual mutant will double in frequency every generation

Question 17

the benefits of sexual reproduction and the disadvantages of parthenogenetic

Answer 17

• Two ways to make new genotypes:
• new mutations
• new combinations (recombination, reassortment)
• Recombination brings beneficial mutations together
• Recombination breaks associations with deleterious mutations

Question 18

Recombination brings beneficial mutations together: increases the rate of adaptation

Answer 18

• Takes longer in asexuals (much faster in sexual reproduction) for independent beneficial mutations to come together in the same individual genotype
• Asexual lineages with different beneficial mutations end up competing with each other, this is called clonal interference

Question 19

The Red Queen hypothesis & how it relates to the paradox of sex

Answer 19

always running just to stand still
really strong selection to change geneone just to not go anywhere
usually changing involves pathogens so changing just to keep up with someone else that is changing

asexual is great until they have to adapt to other factors in the environment, this is where sexual reproduction is better

Question 20

Snails, sex versus parthenogenesis, & resistance to parasites

Answer 20

new zeland mud snails evolution and their parasites
some lakes had more asexual clones than others also sexually reproduce

Question 21

Potamopyrgus antipodarum
New Zealand mud snails:

Answer 21

A mixture of obligate sexuals and obligate asexuals
Microphallus sp. trematode parasites
get into the mud snails and seralize them-> negative effects on fitness-> get eaten by ducks where parasites do not damge

Question 22

Evidence from a New Zealand snail for the maintenance of sex by parasitism

Answer 22

Sexual snails are more abundant when parasitism is high
proportion of sexual reproduction
(females just make clones of themselves so
males would only be involved in sexual reproduction)

Question 23

Infection Dynamics in Coexisting Sexual and Asexual Host Populations: Support for the Red Queen Hypothesis

Answer 23

sexuals gets infected less than asexuals
this is bc sexuals can change and shift genonetypes faster and adapt

Question 24

2000 paper about snails

Answer 24

no sexual clones, just looking at the Parthenogenetic

Question 25

2000 paper about snails what did they do (sympatric)?

Answer 25

first half is he's basically taken different clones of snails and exposed them to the parasite that they would encounter in their native lake at that time - has a bunch of common and rare clones and exposed them to the parasites

Question 26

2000 paper about snails results (sympatric)?

Answer 26

* The common asexual clones get infected and a very high rate (more than 80% or sometimes 100%) - the parasite is locked onto the common one * the ones that are rare are still asexual but the parasite isn't locked in on them and it's only infecting them at about 60% So the common ones will eventually become more and more sterile and the rare ones will become more common and then the parasite is gonna adapt to be able to infect it When there is the parasites sexual ones are better because they can shuffle and evolve faster

Question 27

2000 paper about snails what did they do (allopatric)?

Answer 27

They took the same clones and exposed them to parasites from a different lake

Question 28

2000 paper about snails results (allopatric)?

Answer 28

The infection is much, much lower, so less than 20% shows that it isn't something inherent about those a sexual clones - the common ones are not always acceptable to parasites

Question 29

what happens when there are mixed infections

Answer 29

two different flu strains come together in the same host can come together and mix/reassort Viruses (and other pathogens & microbes) can also recombine

Question 30

Recombination breaks associations with what mutations

Answer 30

deleterious

Question 31

example of unlinked

Answer 31

AB AB Ab Ab aB aB ab ab

Question 32

example of linked

Answer 32

AB AB AB AB ab ab ab ab

Question 33

Linkage disequilibrium (LD)

Answer 33

* Non-random association of alleles at different loci (combinations of alleles that are more or less common than expected) * Linkage disequilibrium can be caused by many things, including: - reduced recombination due to physical linkage (most common reason) - inbreeding - natural selection

Question 34

Genetic hitchhiking

Answer 34

When selection favours an allele at one locus, alleles at nearby linked loci may also increase in frequency, even if they are neutral - important in the concept of beneficial mutations 1. Beneficial mutation arises and increases in frequency and spreads through the population and replaces and out competes other alleles at the same locus 2. The neighbors (linked sites) that are not beneficial, also increase in frequency 3. Overtime you get recombination that breaks up association with the beneficial mutation

Question 35

“Ruby in the rubbish”

Answer 35

when beneficial mutations are stuck in linkage with deleterious ones ruby is beneficial mutations and rubbish is baggage of the deleterious mutations that are stuck to the benefit (neighbor)

Question 36

“Muller’s ratchet”

Answer 36

deleterious mutations will accumulate in small asexual populations keep advancing in steps and there is not turning back - asexual reproduction (no reshuffling) - small popualtion size (no genetic drift)

Question 37

Muller’s ratchet

Answer 37

* in small asexual populations, the class of individuals with the lowest # of deleterious mutations can be lost by chance (& never recovered!) * this process continues, leading to an irreversible decline in fitness my notes: - once you have deleterious no getting away from it - small pop-> can completely lose individual bc of deleterious mutation - this is why sexual reproduction is important bc it if it gets a deleterious mutation it can get rid of it not doomed

Question 38

Sex speeds adaptation by altering the dynamics of molecular evolution Michael J. McDonald1,2*, Daniel P. Rice1,2* & Michael M. Desai1,2,3

Answer 38

EXPERIMENTAL EVOLUTION Over 1000 generations, experimentally evolved yeast strains that only differed as to whether they a) only reproduced asexually, or b) underwent sexual reproduction every 90 generations wanted to make sure comparisons were as similar as possible Something about freezing and comparing?

Question 39

Michael J. McDonald1,2*, Daniel P. Rice1,2* & Michael M. Desai1,2,3 results

Answer 39

Higher fitness increase in sexual than asexual lines evolved lines all did better Deleterious mutations become fixed in asexual lines, but never in sexual ones - they can isolated what mutations were the ones that became fixed and figure out if they are beneficial or deleterious - deleterious become fixed -> neighbors that get pulled along - lots of beneficial become fixed - both beneficial and deleterious are dynamic - deleterious never make it (become fixed) bc sexual reproduction gets rid of deleterious

Question 40

Different types of mutations get fixed in sexual than asexual lines (Why?)

Answer 40

difference in the types of mutation that got fixed in the sexual compared to the asexual biggest difference: fixed - no synonymous that became fixed in sexual - almost no intergenic became fixed in sexual remember the fixed are the ones that made it and become 100%

Question 41

Reproductive modes with combinations of sex & asex

Answer 41

* Cyclical parthenogenesis (alternating cycles of sex & asex) - best of both worlds * Selfing(with rare outcrossing)

Question 42

The amount of recombination also varies a great deal within genomes

Answer 42

Some parts of the genome exhibit little or no recombination (they are asexual), with huge consequences

Question 43

what part of our genome has no recombination

Answer 43

1. mitochondria 2. y chromosomes - do not recombine have virtually no genes (eg, human Y encodes only ~30 distinct proteins) are littered with noncoding DNA - much lower polymorphism - dont have anyone to combine with - pic not included 3. centromeres and thomeres 4. chloroplasts

Question 44

Case study: A high incidence of parthenogenesis in agricultural pests results

Answer 44

if parthenogenesis is as frequent in pest species as in non- pest species, then a straight line with a slope of 1 is expected * but instead we see all the families of different insects are way above the one to one to the left so they are over represented * A higher percentage of them are of the ones that are pests-> A higher percentage of Parthenon genetic