Chapter 24 Flashcards
Phenotypes fall on a range without clear division: quantitative, continuous. Why are they called continuous?
- exhibit a spectrum of possible values
- trait can vary smoothly across a continuum than falling into distinct categories
Why is the relationship of phenotype to genotype complex?
What type of inheritance does this contribute to?
- due to multiple genes/loci
- polygenic inheritance
What is the unabbreviated version of QTL?
quantitative trait loci
What strongly influences multifactorial characteristics?
- loci
- environment
What does meristic mean?
- whole numbers
- traits that are countable and can’t be continuous
Define threshold characteristics?
- two phenotypes
- underlying quantitative inheritance (disease susceptibility)
What does it mean when alleles are additive at all loci?
- for every gene involved in a trait, each allele contributes a predictable amount to the overall phenotype
- no interaction between alleles at different loci
Give an example of “additive, but not equal”
A+A+B-B- = A-A-B+B+
A+A+ does not = B+B+
Can environmental influences make characteristics more continuous?
yes
What does a normal distribution curve look like?
- a simple hill
- “bell-shaped”
What does a skewed distribution curve look like?
large hill, then decrease in hill height
What does a bimodal distribution curve look like?
- two hills
- one large, one medium
For normal distribution, what is the “mean”?
What’s its unit?
- average
- (line over) X
What is standard deviation (s)?
- calculated from the variance
- measuremnet of how far the typical individual is from the mean
What does it mean when the value are high for standard deviation?
Low?
high:
- wide curve
low:
- narrow curve
How do you calculate variance form standard deviation (s)?
variance = (standard deviation)^2
= s^2
What does correlation measure?
how strongly the values of two different quantitative characteristics relate to each other
What does it mean when the correlation value is 1?
0?
-1?
1:
- perfect correspondence (one is perfectly proportional to the other)
0:
- no correspondence (no relation between the two characteristics)
-1:
- perfect correspondence (inversely proportional)
What does it mean when the correlation between parental values and offspring is high?
- higher genetic contribution to the characteristics
- lower environmental contribution
What does regression measure?
What is it used for?
- how two characteristics relate to each other
- predict the actual value of one characteristic, given the value of the other
What is regression coefficient?
the slope of the regression line
What is the formula that corresponds to population variance?
Vp = Vg + Ve + Vge
Within the population phenotypic variance function Vp = Vg + Ve + Vge, what is Vg?
Ve?
Vge?
Vg:
- genetic variance
- all different contributions to phenotype
Ve:
- environmental variance
- contribution of environmental factors to phenotypic variance
Vge:
- genetic-environmental interaction variance
- contributes to phenotypic variance
- environment factors may have different effects on genotypes
What are the components of genetic variance (Vg)?
Vg = Va + Vd + Vi
Withing the genetic variance formula (Vg = Va + Vd + Vi), what is Va?
Vd?
Vi?
Va:
- additive variance
- genetic component of phenotypic variability at a loci
- phenotype of Aa may be the average of AA and aa
Vd:
- dominance genetic variance
- Aa may not be the average of AA and aa
Vi:
- genic interaction variance
- alleles at different loci may interact and not be additive
What does the phenotypic variance formula look like when Vg is substituted with its components?
Vp = (Va + Vd + Vi) + Ve + Vge
Whar are the two types of heritability?
- broad-sense heritability
- narrow-sense heritability
What does it mean when broad-sense heritability is equal to zero?
1?
0:
- no genetic component
- all phenotypic variation is environmental
- offspring would resemble their parent similar as a stranger would
1:
- genetic component completely accounts for all phenotypic variance
- offspring will resemble parents exactly
What is commonly the value of broad-sense heritability?
What does this mean?
0.5
- genetic and environmental components of variance are similar magnitudes
What is the formula for broad-sense heritability?
narrow-sense heritability?
broad:
H^2 = Vg/Vp
narrow:
h^2 = Va/Vp
What is the difference between broad-sense heritability and narrow-sense heritablility?
broad:
- includes all genetic components
narrow:
- includes just additive and phenotypic variance
What is narrow-sense heritability used for?
predicting the inheritance of quantitative traits
Why can’t you eliminate environmental variance by growing/raising individuals in identical environments?
it is impossible for two environments to be exactly the same
What is one way to eliminate genetic variance (Vg)?
What would be the new phenotic variance formula?
- inbreeding or cloning individuals
Vp = Ve
What is another formula for broad-sense heritability?
H^2 (varying population) = (Vp (varing population) - Vp (identical population)) / Vp (varying population)
What is artificial selection applied to?
members of a parental population
What is the formula for narrow-sense heritability (h^2)?
h^2 = R/S
Within the formula for narrow-sense heritability (h^2) (h^2 = R/S), what is R?
S?
R = response to selection = x (original) - x (offspring)
S = selection differential = x (original) - x (selected)
