Exam 4 Quantitative Genetics Flashcards
Qualitative trait
Only a few distinct phenotypes
Quantitative trait
continuously variable over some measure
Polygenic
many genes involved
Environment
different genotypes perform differently based on their environment
Quantitative traits are variable due to
polygenic and environment
Oligogenic
multiple genes but not as many as Poly, more than 1 but less than 10
Model
some belief in how something behaves
Threshold
must be reached before the trait is expressed. Example-diseases
The difference between the inheritance of genes influencing quantitative characteristics and the inheritance of genes influencing discontinuous characteristics is in
the number of loci that determine the characteristic
(1/4) to the nth power where n=
number of biallelic loci
Mean
provides information about the center of distribution
average
Variance
indicates the variability of a group of measurements, or how spread out the distribution is
Standard Deviation
square root of variance
Covariance
how two measurements vary together ranges from negative infinity to infinity
Correlation
the strength of association between two measurements. Ranges from -1 to 1
Correlation (does/doesn’t) equal causation
DOESN”T
Regression
linear relationship between two variables. allows predictions to be made
y=mx+b
Heritability
the proportion of the total phenotypic variation that is due to genetic differences
Va
additive
additive effects of genes on the phenotype, which can be summed to determine the overall affect on the phenotype
Vd
Dominance
alleles at a locus are not additive, the affect of an allele depends on the identity of the other allele at the locus
Vi
interaction
Epistatic effects (masking)
Ve
environment
differences resulting from environmental factors
Vge
Gene by environment
effect of gene depends on environment it is found in
How to calculate Vp
Va+Vd+Vi+Ve+Vge
How to calculate Vg
Va+Vd+Vi
Are plants or animals affected more by the environment
plants
Broad sense heritability
H2 represents the proportion of phenotypic variance that is due to genetic variance
H2= Vg over Vp
Narrow sense heritability
h2 represents the proportion of phenotypic variance that is due to additive genetic variance. “resemblance between parents and offspring”
h2=Va over Vp
Calculating heritability
- eliminating one or more variance components
- comparing the resemblance of parents and offspring
- comparing the phenotypic variances of individuals with different degrees of relatedness
- measuring the response to selection
Response to selection
the extent to which a characteristic subjected to selection changes in one generation
Selection differential
the difference between the mean phenotype of the selected parents and the mean phenotype of the original population
Mendelian population
is a group of interbreeding, sexually reproducing individuals that have a common set of genes- the gene pool
Genotype frequency
number of individuals with that genotype over total number of individuals
Allele Frequency
Number of copies of the allele over number of copies of all alleles at the locus
p+q=
1
P is assigned to the
higher frequency trait
Hardy Weinberg Equilibrium
Assumptions
1. diploid
2. sexual reproduction (independent assortment)
3. non-overlapping generations
4. bi-allelic (easily extended to multiple alleles)
5. Equal allele frequencies in male and females
6. Random mating
7. no mutation
8. no migration
9. no natural selection
10. large population (no drift)
Predictions of Hardy Weinberg Equilibrium
- allele frequencies do not change
- Genotype frequencies reach equilibrium after one generation with proportions
p2 (AA) + 2pq (Aa) + q2 (aa)
Hardy Weinberg is per
locus
Implications of Hardy Weinberg Equilibrium
1.population cannot evolve if it meets the assumptions
2.Genotypic frequencies are determined by the allelic frequencies
3. A single generation of random mating produces the equilibrium frequencies
Chi squared formula
(observed - expected)squared over expected
Positive assortative mating
tendency for like individuals to mate
Negative assortative mating
tendency for unlike individuals to mate
Outcrossing
preferential mating between unrelated individuals
inbreeding
preferential mating between unrelated individuals
leads to increased homozygosity
does not change allele frequency
Inbreeding coefficient
F
a measure of the probability that two alleles are identical by descent
ranges from 0 to 1
inbreeding coefficient of 1 means
all alleles are identical by descent
inbreeding coefficient of 0 means
mating is occurring randomly in a large population
Mutation
ultimate source of variation
Migration causes
the gene pools of two populations to become more similar
adds genetic variance to populations
Genetic Drift is
sampling difference that arises when gametes unite to produce progeny
the amount of genetic drift can be estimated from the
variance in allelic frequency
Genetic drift equation
pq over 2 N
N=number of individuals in a population
Causes of genetic drift
all genetic drift arises from sampling
reduced population size
founder effect
bottleneck
founder effect
establishment of a population by a small number of individuals
bottleneck
when a population undergoes a drastic reduction in size
Effects of genetic drift
produces change in allelic frequencies within a population
reduce genetic variation within populations
different populations diverge genetically from one another over time
Natural selection
takes place when individuals with adaptive traits produce a greater number of offspring than do individuals not carrying such traits
Effect of natural selection depends on
fitness values of the genotypes in the population
Fitness (W)
defined as thee relative reproductive success of a genotype
ranges from 0 and 1
Selection coefficient
the relative intensity of selection against a genotype
