Lecture 17 - 27 Key Topics Flashcards
What is introgression
Transfer of genetic material between species through hybridisation and repeated back crossing
What is the biological species concept?
defines a species as a group of organisms that can interbreed and produce fertile offspring in nature.
what are pre-zygotic and post-zygotic barriers?
Pre-zygotic - barriers that prevent the egg from being fertilised
Post-zygotic - barriers that reduce viability or reproductive capacity of the offspring
What are operons?
several genes, next to each other in prokaryotic DNA, that are transcribed as a single piece of mRNA.
What is antagonist pleiotropy?
single gene affects more than one trait related to fitness.
What are introns?
Non-coding sequences of DNA, found in eukaryotes only
What is a lac operon
Transcriptional unit in bacteria that contains genes needed for lactose metabolism.
what is the “pull of the present”?
An upward trend in recent diversification due to the speciation event appearing closer to the present
What is co-speciation?
co-evolution of host and symbiont lineage
Examples of pre-zygotic and post-zygotic barriers.
Pre-zygotic:
Temporal isolation - different reproductive cycles or different period of activity
Behavioural isolation - different courtship patterns
Geographical isolation - occupy different habitats or niches within the same region
Post-zygotic:
Hybrid inviability - not viable
Hybrid infertility - not fertile
Hybrid breakdown - breaks down
What is phylogenetically independent contrast?
It is a method to compare traits on sister clades where one clade has the trait and the other does not
What is alloploidy speciation?
What is homoploid hybrid speciation?
From of speciation where hybridisation between two species results in a new species with a duplicated genome.
formation of new species through hybridisation without genome duplication.
What role does selection play in hybrid species?
Selection removed incompatible allele combinations (BDMIs), leaving only viable genetic mixes in hybrids.
What is the morphological species concept?
Organisms that appear morphologically identical. Can be misleading due to mimics and cryptic species.
Why do mitochondrial sequences form a single tree?
Because no recombination occurs in mitochondrial DNA (mtDNA)
what is monophyly in gene trees?
describes a group of organisms that share a common ancestor and all of its descendants. Evolving over time due to genetic drift.
What are BDMIs?
Genetic incompatibilities that occur post zygotically, reducing hybrid fitness and contributing to reproductive isolation.
What is adaptive introgression?
Transfer of beneficial allele through hybridisation between species.
What is the mutation accumulation theory?
Harmful mutations accumulate because selection weakens later in life
convergent evolution
when species that are not closely related evolve similar features or behaviours independently.
antagonistic pleiotropy theory of aging
suggests that genes beneficial early in life may have detrimental effects later on
disposable soma theory of aging
suggests trade-off between reproduction and maintenance due to a limited energy budget
what are the key trade-offs in life strategies?
growth vs reproduction
early-life reproduction vs survival and future reproduction
offspring number vs offspring size and survival
what drives early vs late maturation?
high juvenile deaths favours delayed reproduction.
high adult mortality rates favour early reproduction.
why are some mutations not parsimoniously informative?
they occur in only one taxon and do not provide information about shared ancestry
3 requirements of natural selection
Variation in traits.
Some of that variation must be heritable
There must be competition (different fitness levels)
Define exaptation
trait being used for something different than it was originally evolved for
parallel evolution
two species evolve similarly independently, but their changes do not affect each others fitness
key points of life history trade-offs
Larger body size correlates with greater fecundity (the ability to produce an abundance of offspring or new growth; fertility)
A negative relationship exists between time and survival
there’s a trade-off between individual offspring investment and number
there is an optimal size and age for reproduction ro maximise fitness.
inartistic and extrinsic mortality
inartistic - internal physiological factors like ageing.
extrinsic caused by external factors like predation.
what is senescence
the persistent decline in age-specific fitness due to internal physiological deterioration
limits of co-evolution
lack of heritable traits, weak or inconsistent selection pressure, environmental variability disrupting interactions
inter-loci sexual conflict
male seed beetles damaging female reproductive tracts to prevent re-mating. leads to evolutionary arms race between the sexes.
how is fitness measured in selection?
Fitness (W) measures survival/reproductive success. For a genotype A1A1:
W11 = 1 (highest fitness, reference)
W12 = 0.9
W2z = 0.8
Selection coefficients:
S11 = 1 - W11 = 0
S12 = 1 - W12 = 0.1
522 = 1 - W22 = 0.2
intra-loci sexual conflict
male and female traits hare the same genetic loci but have different optima.
Hamiltons’s rule
Altruism evolves if rxb>c
r is relatedness
b is benefit to recipients
c is cost to the donor
how does mutation affect allele frequencies?
introduces new alleles
effect of migration on allele frequency
increases
why do family conflicts arise
difference in investment in gametes of males and females. Different in potential investment required for offspring success.
concept of inclusive fitness
combines direct fitness (personal reproduction) and indirect fitness (helping relatives reproduce)
why is sexual selection described as a subset of natural selection?
it focuses specifically on traits that increase mating success rather than overall survival, driven by competition and mate choice.
Consequences of sex chromosome linkage in intra-loci conflict
can lead to selective pressure removing harmful alleles from one sex over another, causing potential chromosome shrinkage.
assortative and disassortative mating
Assortative mating is when individuals tend to mate with others who are similar to them, while disassortative mating is when individuals tend to mate with others who are different from them
what is selection coefficient(s)
selection coefficients measure the relative disadvantage of genotypes compared to the fitness genotype, influencing how quickly allele frequencies change.
what physical traits are selected for in intra-sexual selection?
size and weaponry
are males under strong selection pressure?
yes, males are often under strong selection pressure
because the males are better at fighting off other males, or because females will choose to mate with the bigger or more decorated males.
what is required for sexual selection to occur?
distinct sexes within the population
what is mate guarding?
physically guarding the female, extending copulation (sex), or using copulatory plugs.
what is over dominance in fitness?
when heterozygotes have higher fitness than either homozygote, maintaining both alleles in the population.
what does random mating ensure in HWE?
that genotype frequencies match the expected proportions (p^2, q^2, 2pq) after one generation.
relationship between migration rate and genetic diversity?
high migration rates increases genetic diversity by introducing new alleles.
low rates can lead to population diversification.
what physiological trait is selected in intra-sexual selection?
sperm production
what is the Hardy-Weinberg Equilibrium null model?
it is a model for a sexually reproducing diploid population with random mating. It predicts three genotypes with expected frequencies
Homozygous (AA): p^2
Homozygous (TT): p^2
Heterozygous (AT): 2pq
Do sexual reproduction and sexes always coexist?
No, organisms that produce equal-sized gametes do not always have distinct sexes.
What are the main explanations for cooperation?
Collective self-interest (e.g. group hunting)
Mutual benefit (e.g. reciprocal altruism)
Kin selection (e.g. inclusive fitness)
What is sex chromosome linkage in intra-loci conflict?
Sex chromosome linkages occurs when sexually antagonistic genes are located on sex chromosomes, influencing the evolution of traits like colouration or courtship behaviours.
why does sexual selection occur more strongly in one sex than another?
Sexual selection occurs more strongly in the sex with the lower parental investment.
This is because they have more to gain by increasing mating opportunities, while the other sex is more selective due to higher investment in offspring.
what happens in relation to alleles when HWE assumptions are violated?
Drift: Increases fluctuations in allele frequencies, especially in small populations.
Selection: Alters allele frequencies based on fitness differences.
Mutation: Introduces new alleles
Migration: Adds alleles from other populations
How does sexual antagonism affect fitness?
Sexual antagonism occurs when the same gene has contrasting effects on male and female fitness often resulting in suboptimal traits for one sex (e.g. bright coloration in guppies)
why is group selection not an evolutionary stable strategy (ESS)?
a group selection fails as an ESS because selfish individuals that act against the group’s interests can invade and outcompete altruistic individuals.
how do mutation and migration differ in their effects on allele frequencies?
Mutation: introduces new alleles, often at low frequencies.
Migration: introduces or redistributes alleles between populations, affecting allele frequencies based on the migration rate and source population.
How do conflicts occur during pregnancy in mammals?
genetic conflict between maternal and parental genes controlling offspring growth.
Example: insulin-like growth factor (IGF2) in rates, regulated differently by maternal and parental genes.
What is evolutionary sexual conflict?
conflict over traits benefiting one sex but harming the other.
Example include inter-loci sexual conflicts (arms race) and intra-loci sexual conflict (tug of war over optimal traits).
how do you calculate the inbreeding coefficient (F)?
F = 1 - Hobserved/2pq
Hobserved is the observed heterozygosity and 2pq is the expected heterozygosity.
what are the differences between inter-loci and intra-loci sexual conflict?
inter-loci sexual conflict: traits are controlled by different loci in males and females, often leading to an arms race
intra-loci sexual conflict: traits are controlled by the same loci but have two different fitness optima in males and females, leading to a “tug-of-war”
