Exam 3 pt 3 Flashcards
balancing selection
not evolving toward allele fixation or elimination (more of a flat bell curve)
balacing selection
not evolving toward allele fixation or elimination (more of a flat bell curve)
balancing selection occurs because of a
- heterozygote advantage
- negative frequency dependent selection
selection coefficient
looks at the degree to which a genotype is selected against
s = 1 - w
heterozygote advantage will reach equilibrium when
sAAp = saap
negative frequency dependent selection
rare individuals have a higher fitness than more common individuals
* selection always favors less numerous genotypes
* drives towards balance
disruptive selection
favors survival of two or more different genetypes with different phenotypes
disruptive selection typically acts on
traits determined by multiple genes
disruptive selection is likely to occur
in populations with diverse/different enviroments
stabalizing selction
extreme phenotypes are selected against
stabalizing selection tends to
decrease genetic diversity
* elimination of alleles that cause variation in phenotypes
genetic drift
random changes in allele frequencies due to random fluctuations
genetic drift
random changes in allele frequencies due to random fluctuations
over the long run, genetic drift
favors either the loss or the fixation of an allele
_ populations have more chance of fixation due to genetic drift
smaller
expected number of new mutations
= 2N mu
N - number of indi
mu - mutation rate
a new mutation is more likely to occur in a
large population
the probability of fixation is
the same as the initial allel frequency in the population
when N is large
- higher chance of new mutations
- higher chance of mutations being eliminated
when N is large
- higher chance of new mutations
- higher chance of mutations being eliminated
when N is small
- lower chance of new mutation
- new mutatiosn have a larger chance of being fixed
average number of generations to achieve fixation
t = 4N
alelle fixation takes longer in
large populations
bottle neck effect
population randomly eliminates genotypes, no selection, diversity goes down
could be due to a natural disaster
founder effect
a small group of individuals seperates frrom a larger group and starts its own popiulation that all originate from that small group
consequences of founder effect
- founding population has less genetic variation than original population
- allelic frequencies of founder population differ from the original population
gene flow
the transfer of alleles from donor population to recipient population
consequences of bidirectional migration
- reduces allel frequencies differences between populations
- enhances genetic diversity within a population
assortive mating
individuals do not mate randomly
* positive: mate bc of similar phenotypes
* negative: mate bc of dissimilar phenotypes
inbreeding coefficient
probability that teo alleles for a given gene in an individual will be identical because of a common ancestor
inbreeding coeficient
sum of (0.5)n(1 + Fa)
n = number of indiv in inbreed path
Fa = breeding coef of common ancesto
inbreeding coeficient
sum of (0.5)n(1 + Fa)
n = number of indiv in inbreed path
Fa = breeding coef of common ancesto
fixation (inbreeding) coefficient
probability that an allele will be fixed in the homozygouse condition
the value of the fixation (inbreeding) coeff increases as
population size decreases
frequency of genotypes in inbreeding
AA = p2 + fpq
Aa = 2pq(1-f)
aa = q2 + fpq
inbreeding effects on gentype frequencies
hetrozygote goes down while homozygotes go up
inbreeding depression
in natural populations, inbreeding lowers overall fitness
For a quantitative trait that is polygenic, which of the following would tend to promote a continuum of phenotypes?
* Increasing the number of genes that affect the trait
* Decreasing the effects of environmental variation
* Increasing the mutation rate
Increasing the number of genes that affect the trait
variance is
- a measure of the variation around the mean
- computed as a squared deviation
a QTL is
a site on a chromosome where one or more genes affected quantitative traits are located
a genotype–environment interaction.
two more more genotypes noto affected the same way
In a population of humans, the correlation between height for fathers and their adult sons is 0.24. What is the narrow sense heritability for weight in this population?
Note: hN2 = robs/rexp
0.48
The mean weight of cows in a population is 520 kg. Animals with a mean weight of 540 kg are used as parents and produce offspring that have a mean weight of 535 kg. What is the narrow-sense heritability (hN2) for body weight in this population of cows?
Note: hN2 = (Xo − X)/(Xp − X)
Where
X is the mean weight of the starting population Xo is the mean weight of the offspring Xp is the mean weight of the selected parents
0.75
genotype enviroment association
certain genotypes found in a particular enviroment
quantitative genetics
study of traits that can be described numerically and varies measurably
frequency distribution
Quantitative traits do not naturally fall into a small number of
discrete categories
An alternative way to describe them is a frequency
distribution
* To construct a frequency distribution, the trait is divided
arbitrarily into a number of discrete phenotypic categories
Be able to do the following types of calculations: mean, variance, standard deviation, covariance, and correlation (see Section 28.2, Figure 28.2).
ope
polygenic inheritance
transmission of traits that are governed by two or more genes
if r > 0
as one factor increases, the other factors will increase with it
r = 0
the two factors are not related
r < 0
as one factor increases, the other will decreases
An r value that is statistically significant need not imply a
cause-and-effect relationship
quantitative trait locus
The location on a chromosome that harbors one or more
genes that affect the outcome of a quantitative trait
If VG is very high and VE is very low
Genetics is more important in promoting phenotypic variation
If VG is very low and VE is very high
The environment causes much of the phenotypic variation
phenotypic variance
sum of genotic variance and enviromental variance
genotype-environment association
When certain genotypes are preferentially found in a
particular environment
heritability
the amount of phenotypic variation within a
group of individuals that is due to genetic variation
If all the phenotypic variation in a group was due to genetic
variation
* Heritability
would have a value of 1
heribility value of 0
If all the phenotypic variation was due to environmental factors
narrow sense heritability
The heritability of a trait due to the additive effects of alleles
= r obs / r exp
selective breeding
the modification of phenotypes in plant and animal species of economic importance by human intervention
selective breeding leads to
ppopulation becoming monomorphic
selection limit
when the population starts becoming monomorphic, more selective breeding have no effect
realized heritability
estimating narrow sense heritability
Xo - X / Xp - X
realized heritability
estimating narrow sense heritability
Xo - X / Xp - X
heterosis
when inbred strains are crossed to each other and the offspring are more vigorous than either parent
