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Although we generally think of plants and animals as having sexual reproduction, many species can reproduce sexually or asexually. As a consequence, populations of the same species can differ in the proportion of reproduction that is sexual vs. asexual. How will this influence linkage disequilibrium between two loci?

a. Linkage disequilibrium will be relatively high in populations with high frequencies of sex because recombination tends to create linkage disequilibrium.

b. Linkage disequilibrium will be relatively low in populations with high frequencies of sex because recombination tends to create linkage disequilibrium.

c. Linkage disequilibrium will be relatively high in populations with low frequencies of sex because recombination tends to destroy linkage disequilibrium.

d. Selection will tend to destroy linkage disequilibrium in high sex populations.

e. Selection will tend to destroy linkage disequilibrium in low sex populations.

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Lelia Lubowitz
Lelia LubowitzLv2
29 Sep 2019

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True or False? Mate choice is important onanimal species behavior. Male and female animals often differ inthe cost of reproduction and therefore have different behaviors

True or False? Natural selection is the sum ofsurvival and fertility mechanisms that affect reproductivesuccess.

Question!

Water fleas, Daphnia magna, can switch betweenasexual and sexual reproduction cycles. Which of the followingobservations support the hypothesis that sex is favored inunpredictable environments?

Select one:

a. The introduction of predators triggers sexualreproduction.

b. D. magna reproduces asexually every other generationin a variety of habitats.

c. D. magna reproduces sexually when its aquatichabitat dries up.

d. Asexual D. magna strains outcompete introducedcompetitors.

e. A and C

Question

Reciprocal altruism can be best explained with a model proposedby Trivers in 1971: If one individual (A) pays some cost to helpanother individual (B), but the cost is recovered at some point inthe future (when B helps A), then natural selection might favorbehaviors that lead to this type of reciprocity. In which of thefollowing situations is reciprocal altruism likely to occur?

Select one:

a. in dynamic large populations where individuals rarelyinteract with the same set of partners

b. in eusocial groups such as termites, ants, and other suchspecies

c. in large populations of marine invertebrates

d. in stable groups, with ongoing interactions with the same setof partners

Q1. What is the founder effect?

Sampling error that occurs during the establishment of a newpopulation by a small number of migrants.

Strong natural selection acting on the founders of a newpopulation because the environment they are now living in is sodifferent from the environment they came from.

A phenomenon named after William Founder, who observed that toppredators generally have low genetic diversity.

Rapid population growth following a bottleneck.

Q2. The effects of genetic drift are more pronounced in largerpopulations.

True

False

Q3. Inbreeding tends to increase the proportion of homozygousindividuals in a population (i.e. individuals that have two copiesof the same allele).

True

False

Q4. The effective size of a population is:

The size of an idealized randomly-mating population that is notunder selection and has the same heterozygosity as the actualpopulation.

The size of an idealized randomly-mating population that has thesame heterozygosity as the actual population, but does not loseheterozygosity over time.

The size of an idealized randomly-mating population losinghomozygosity at the same rate as the actual population.

The size of an idealized randomly-mating population losingheterozygosity at the same rate as the actual population.

Q5. Which of the following tends to reduce the effective size ofa population?

Check all that apply:

Increasing the population size.

A biased sex ratio.

Non-random mating.

Q6. If gametes from a gene pool combine randomly to make only asmall number of zygotes, the allele frequencies among the zygotesmay be different than they were in the gene pool because:

The effects of natural selection are more pronounced in smallpopulations.

The effects of genetic drift over several generations are morepronounced with small numbers of gametes.

The effects of differences in frequencies for different allelesare more pronounced with small numbers of zygotes.

The effects of sampling error are more pronounced with smallsamples.

Q7. Genetic drift is different from natural selectionbecause:

In natural selection allele frequencies change because somealleles confer higher fitness, whereas in genetic drift allelefrequencies change because of chance sampling error.

Natural selection acts primarily in large populations, whereasgenetic drift acts primarily in small ones.

Natural selection is a mechanism of evolution, whereas geneticdrift is an outcome of evolution.

Natural selection tends to cause rapid evolution, whereasgenetic drift tends to cause slow evolution.

Q8. Imagine a population evolving by genetic drift in which thefrequency of allele K is 0.65. What is the probability that at somepoint in the future allele K will drift to a frequency of 1?

Q9. A dwindling population of 1000 frogs occupies an isolatedwatershed in Costa Rica. To help preserve the species, scientistscaught 20 frogs to start a new population in a nearby watershed.This species has a gene that affects eye shape. The 1000-memberwild population has two alleles for this gene: R and r, withfrequencies 0.7 and 0.3, respectively. What will be the allelefrequencies of R and r in the 20-member founder population?

The frequencies will be 0.7 for R and 0.3 for r.

The frequencies will be 1.0 for R and 0 for r.

The expected frequencies are 0.7 for R and 0.3 for r. The actualfrequencies could be different.

The founder populations's allele frequencies will necessarily bedifferent than the source population's frequencies.

Q10. For a population containing 90 females and 10 males, whatis the effective population size, Ne ?

Asexual reproduction: the first step to extinction
When species become asexual they could be taking the first stepto
extinction, say researchers who have been studying the geneticstructure
of Penicillium marneffei, an asexual fungus only found in parts ofsouth­
east Asia. Their research found that although P. marneffei sporeswere
able to spread over large distances on currents of air, they werenot able
to ‘invade’ the new environments in which they landed.
‘We believe the failure of P. marneffei to adapt to newenvironments is
because the fungus has largely dispensed with sexualreproduction.
Without sex, you will not have the mixing of genes it causes,something
all organisms need in order to be able to adapt to newenvironments’, said
a member of the research team. Evolutionary theory predicts thatwhile
asexual organisms can initially prosper and out-compete theirsexual
cousins, they pay a price for being unable to adapt throughthe
recombination of genes caused by sexual reproduction.
DNA typing was used to show that different clones of the fungusare
found in different environments, and the researchers believe thatthe
adaptation of the fungus to these environments is limiting theirability to
adapt to other areas. They believe this is why P. marneffei isonly
endemic to a relatively small area of south-east Asia. Even thoughthe
6_________________________________________________________________
fungus makes spores which can spread over very large distances,the
researchers found that all the samples from any given locationwere
genetically very similar. This led them to the conclusion that thefungus
becomes highly adapted to its local environment, making ithighly
successful there, but stopping it spreading to other areas.
‘By being asexual, P. marneffei is not only limiting its ability toadapt, it
may be at risk of becoming extinct. If it is unable to adapt tonew
environments, it will be unable to adapt to changes in itscurrent
environment. While becoming asexual may provide short term
advantages to a species, in the long term, they are likely to endup in
evolution’s ultimate dustbin – extinction’, concluded a member ofthe
research team

You should introduce your article by very briefly explaining thepurpose of
biological reproduction and touching upon the strategies used toachieve it, then
write your account using the following list as a guide to thepoints you should
discuss in your answer:
? How does asexual reproduction differ from sexual reproduction interms of
the biological processes involved and the genetic diversity andvariation of
the DNA produced?
What are the advantages and disadvantages of asexual andsexual
reproduction?
In terms of survival and adaptation, which reproduction strategy ismore
likely to allow a species to evolve rapidly (or to become extinct)?In your
answer briefly describe the two main mechanisms used to creategenetic
variation. Also, explain the factors and pressures that are likelyto drive the
process of adaptation.

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