Questions tagged [population-genetics]

Questions related to the study of the distributions and changes of allele frequency in a population.

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28
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5k views

Books on population or evolutionary genetics?

I have recently been involved in collaborations that require me to model the population genetics of eukaryotic populations. I fear I may either be "re-inventing the wheel" or making conceptual ...
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Why is the strength of genetic drift inversely proportional to the population size?

I saw a concept on the Internet that says "the strength of genetic drift is inversely proportional to the population size". I don't know why they are inversely proportional? Can somebody explain? ...
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2answers
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Are mutations random?

The following claim Mutations are random or just the use of the expression Random mutations are very common among lay people. The claim is very common among lay people. The claim is often ...
4
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1answer
963 views

Assumptions of Hardy-Weinberg rule

The post Solving Hardy Weinberg problems offers an easy explanation of Hardy-Weinberg rule. The current top answer explicitly does not talk about the assumptions of Hardy-Weinberg. A model makes sense ...
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2answers
833 views

Did Darwin ever reach the conclusion that selection will remove variation?

According to simple models of selection the genetic variance in a population should be reduced by selection. (Fisher's fundamental theorem states that the rate at which a population can evolve is ...
2
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1answer
5k views

Why are the genomes of Humans 99.5% the same?

Human's DNA sequence is said to be roughly 99.5% equal. As far as I understand, this means that if I walked up to you and compared our DNA, the sequence of base pairs would be 99.5% the same. My ...
3
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2answers
6k views

How to interpret the breeders equation?

The univariate breeders equation is defined as, $\ R = h^2 s$ where $\ R $ is the response, $\ h^2 $ is the heritability (additive genetic variation), $\ s $ is the selection differential. The ...
8
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3answers
271 views

How is genetic speciation defined?

What determines speciation at a molecular level? At what point does a scientist determine two lineages are different enough to be considered separate species? Does it have a margin of error?
15
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1answer
342 views

What is the percentage of people living in England in 1500 AD whose lineage is still alive?

This sounds a bit random, but it stems from a lecture in statistical genetics which I attended a while ago. We were shown a population lineage graph from which it was clear that most lineages ...
3
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1answer
165 views

Text Book Recommendation: Organic Evolution

I was wondering if anyone could point me in the direction of any text books on organic evolution? I have recently become interested in the subject and would like to know more. I think an undergrad ...
7
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2answers
899 views

How can someone share 50% of their DNA with their parents yet all humans share 99.9%?

I have heard that humans share 99.9% of their DNA with other humans. I have also heard that a child shares 50% of their DNA with their parents. How do I resolve this apparent contradiction? It has ...
3
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2answers
720 views

How is “selection” best defined?

There is natural selection but there is also sexual selection which some regard as a category of natural selection. There is also artificial selection (by humans). The question is, what is a most ...
2
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1answer
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Why does the number of mutations per individuals follow a Poisson distribution?

I was reading this review. On page 11, left column, first paragraph, one can read: [..] there is a Poisson distribution of the equilibrium number of mutations per individual, if fitness effects are ...
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683 views

Human genetic diversity in Africa in comparison with the rest of the world

Background The claim ... Most of the genetic diversity in humans is in Africa ... is quite common. On Biology.SE, it is easy to find posts that make this claim. Consider for example: Do humans ...
7
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1answer
177 views

Easy derivation of Kimura's approximation for the probability of fixation of a mutation

Kimura's approximation for the probability of fixation of a mutation under selection finds recurrent use in population genetics models till date. I am trying to understand the mathematical basis of ...
6
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1answer
275 views

Variance in Fst in the infinite island model

The most famous result in the study of structured populations come from Sewall Wright. He showed that in an island model, where each subpopulation is of size $N$ and the migration rate is $m$, then ...
3
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1answer
533 views

Genotypes in diploid/haploid cells under mitotic/meotic cell divisions

I am new to genetics , and am stuck with the following question at hand: If $2$ cells with genotypes $(A/a)$ and $(A/a,B/b)$ undergo mitotic and meotic cell divisions respectively, what will be the ...
2
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1answer
6k views

What are Codominant vs Dominant Genetic Markers?

When talking about types of genetic markers, the adjective "dominant" and "codominant" are often used. I don't fully understand their definitions and found contradicting definitions. Foll and ...
8
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1answer
2k views

Effect of sex-ratio on the effective population size

As stated on this wikipedia article, the effective population size $N_e$ when the sex ratio differs from $\frac{1}{2}$ is $$N_e = \frac{4N_mN_f}{N_m+N_f}$$ I understand the biased sex-ratio ...
6
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1answer
934 views

Why does the slope of parent-offspring regression equals the heritability in the narrow sense?

Background ---- Notations and assumptions ---- let $W_{ij}$ be the fitness associated to the genotype $AiAj$. $x$ is the frequency of the allele $A1$ in the population. The frequency of the allele $...
5
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2answers
9k views

Definition of “Effective population size”

Could you explain to me, what is the meaning of "Effective population size ($N_e$)"? I would appreciate an example as well.
4
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1answer
134 views

Polymorphism in number of chromosomes?

The answer to this question, saying that Down Syndrome - a trisomy of human chromosome 21 - is caused by de novo mutation (rather than resulting from standing variation) made me think about ...
3
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4answers
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How is it possible for the absolute fitness to be more than 1?

The wikipedia definition of Absolute fitness is "the ratio between the number of individuals with that genotype after selection to those before selection. It is calculated for a single generation and ...
2
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1answer
452 views

What is a typical value of the selection coefficient s?

I am trying to gain an understanding of the real world effects of natural selection from the equations, especially comparing it with drift. However I have been unable to find any examples which give ...
2
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1answer
3k views

Why is the probability of fixation of an allele equal to its frequency?

Introduction In a panmictic population, the probability of fixation of an allele at a neutral locus is equal to its frequency at that time. I will refer to this probability of fixation as calculated ...
2
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1answer
213 views

What test to apply to detect genomic signatures of selection?

I would like to ask you for your sugestions for selecting a test to detect signatures of selection in the following mouse model: We have three groups: animals exhibiting trait A, trait B and controls....
6
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1answer
245 views

Hill-Roberston effects and effective population size

From this article, first page, middle of the second column: Even if harmful alleles do not become fixed, they can still reduce the efficacy of selection on neighbouring loci through a process ...
5
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2answers
666 views

Coalescence time: Is it different for haploids and diploids in population genetics?

I'm trying to model Cyanobacteria cells divergence in 2 populations with mutation rate $-\mu$ and I need to verify my model with a valid theory. I don't have much biology background and all the ...
4
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2answers
94 views

Interspecies competition and pathogen

Following my answer to this question, a debate ensued on whether the loss in population of one species (namely red squirrels) due to its lesser resistance to a pathogen brought by a competing species (...
3
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1answer
921 views

How do heredity and regression to the mean work with respect to intelligence?

I am trying to understand the heredity of intelligence between generations in general, and how regression to the mean works in detail in particular. The answer I'm looking for should preferably answer ...
7
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1answer
399 views

How to determine whether changes of an allele's frequency are due to genetic drift or selection?

Given that both natural/artifical selection and genetic drift are evolutionary mechanisms that influence how allele frequencies shift in a population: Are there ways to determine whether a frequency ...
5
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1answer
141 views

Learn Bioconductor the hard way!

I came to analyzing population genetics data from the background of a theoretician and a computer biologist but not with the standard tools that a bioinformatician (or empiricist in population ...
4
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2answers
1k views

Initial population when i count backwards?

My question is dealing with how many ancestors it took to produce me: --> to produce me it took 2 people (my parents) = ($2^1$) people = 2 --> one generation further included = ($2^1 + 2^2$) people = ...
3
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1answer
811 views

Ways to distinguish between purifying selection and selective sweep

When looking a population genomic data, regions of low diversity (lower than expected; such as in a region of high recombination) can indicate either purifying selection of deleterious mutations or a ...
2
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1answer
113 views

Effective population size when the population sizes varies from season to season

Let's think of a species which has four generations per year and which population size changes from season to season so that the population size is 100 in summer, 200 in spring, 50 in autumn and 20 in ...
7
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1answer
127 views

Hamilton's derivation of direct fitness from his 1970 paper

In his 1970 paper "Selfish and Spiteful Behaviour in an Evolutionary Model", Hamilton uses Price's equation to derive his well-known rule $rb -c >0$. My question is about one of the steps in his ...
5
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1answer
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How do I calculate the change in allele frequency in a haploid population under selection?

From this book For simplicity, let us consider a haploid organism and assume that the frequencies of alleles $A_1$ and $A_2$ are given by $x$ and $y=1-x$, respectively. We also assume that the ...
4
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1answer
621 views

How could one calculate the gene flow between two populations?

Imagine there are two populations X and Y, and for each population you have the genotypes of each individual in that population (e.g. Aa, AA, aa, etc.), but for multiple loci (e.g. AABb). How could ...
3
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2answers
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Identity By Descent vs Identity By State

Background The concepts of Identity By Descent (IBD) vs Identity By State (IBS) are central in population genetics, yet I fail to fully wrap my head around the definitions. You can find examples ...
3
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0answers
157 views

Inbreeding Coefficient and Coefficient of Relationship

Wikipedia gives the following formula to calculate a "path of coefficient of relationship" between an ancestor $A$ and an offspring $O$: $$\rho_{AO} = 2^{-n} \left( \frac{1+f_A}{1+f_O} \right)^{1/2} =...
3
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1answer
83 views

Altruism in viscous (asexual) populations

The viscosity of a population is the tendency of offspring to remain near their place of birth. Taylor 1992 ("Altruism in viscous populations") provides a model to study how viscosity affects the ...
2
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1answer
87 views

Down syndrome in subsaharan populations

What is the rate of occurrences of Down syndrome in subsaharan African populations? Is it the same as in white European populations? An interesting hypothesis came to my mind: Could it be that Down ...
0
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1answer
55 views

What is the population limit that makes consanguinity an issue?

A recent incident brought in the news one of the last uncontacted people - the Sentinelese: the Sentinelese appear to have consistently refused any interaction with the outside world. ...
8
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2answers
198 views

Would a colony with only one male and female collapse?

This is a thought experiment: If we form a population with only a single founder pair, can this population survive? What would happen? Would this inbreeding cause the population to go extinct? Could ...
7
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2answers
168 views

Within and Between Allelic Class Diversity

I am reading Charlesworth et al. 1997. They talk about diversity within and between allelic classes. Nucleotide diversities ($π$) at each neutral site were estimated from the mean of $2 \sum z_t (...
6
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1answer
110 views

Evolution of diversity and extinction resistance

I saw a comment on an answer to another question that touched on an interesting topic: keeping diversity is useful for parameter exploration or to adapt to future environmental change My initial ...
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0answers
110 views

Isn't heritability more important to genic capture than just genetic variance?

Rowe & Houle (1996) give two criteria for the selection of costly female choice: Condition dependence of sexually selected traits High genetic variance in condition Regarding heritability, ...
4
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3answers
399 views

Is the variance of a trait related to its rate of evolution?

Posed with a question that has me stuck: Is increased variance of a phenotypic trait in a population associated with slower evolution of that trait? I have to either 'disagree or agree' and argue ...
4
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1answer
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Outbreeding depression in humans [duplicate]

Is there any evidence of outbreeding depression in human beings?
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How does the introduction of clones would affect population genetics? [closed]

Since the ability to clone animals gives another way to preserve species, this could help for the breeding process. It has been noted that with the ability to clone animals, endangered species can ...