Quantitative characters Flashcards
Discontinuous can have any numerical value along a scale. True or false?
False - discontinuous characters fall into discrete categories.
There are no intermediates values with discrete data. True or false?
True.
Multiple loci may be responsible for a discrete character. True or false?
True.
Discrete characters can result from genetic variation only, the environment has no effect. True or false?
False - the environment can also play a role in discrete characters.
Give an example of a discrete character that is solely due to genetics.
Snail shell banding pattern: highly polymorphic, variable background colours with banding pattern over the top. There are clear dominance patterns.
Give an example of a discrete character that is made variable by the environment.
Acorn barnacles have 2 shell morphs: can be conical or bent, bent morph is only found in areas where the predator A. angelica is found as it offers protection. An example of adaptive phenotypic plasticity.
Define adaptive phenotypic plasticity.
Whereby the phenotype adapts to changing environmental conditions.
Continuous data can be any numerical value along a scale. True or false?
True.
There are many intermediates with continuous data. True or false?
True.
Variation in continuous traits is usually driven by a combination of both genetic and environmental influences. True or false?
True.
Continuous traits are always determined by a single gene. True or false?
False - continuous traits are NEVER determined by a single gene!
How are continuous traits usually assessed?
Related individuals are compared. Specifically, ‘do the progeny represent the parents or the population average’?
If the progeny represent the parents, it is likely the trait is determined by…?
Genetics
If the progeny represent that population average, it is likely the trait is determined by…?
The environment
Why are experiments whereby the progeny are compared to the parents often misleading?
Because the progeny share an environment with the parents as well as genetics.
What is cross-fostering and what is the point of it?
Offspring are taken from their birth parents and raised in another family, then we can be sure that any similarity to the birth parents is down to genetics.
Briefly outline an experiment with homozygotes to illustrate how multiple loci are involved in continuous traits.
- Take 2 lines that are different homozygotes at the same loci, i.e. hom dom and hom rec
- Create an F1, they will be heterozygotes and parental intermediates if variation in environmental
- Self-fertilise to create an F2
- Self-fertilise to create an F3
- At each level there should more and more variation within the progeny and between the progeny and the parents, meaning there is a larger spread of values.
‘As the number of loci controlling a trait increases, then the phenotypic frequency distribution becomes continuous’
Give an example of how homozygotes can indicate environmental variation.
Tobacco plants that are homozygous for corolla length still display flowers of varying lengths.
There are many loci involved in continuous traits and each one has a large effect on the phenotype. True or false?
False - each loci has a relatively small effect on the phenotype.
There are models for how multiple loci interact in continuous traits. What is the simplest model?
Additive model whereby alleles have + or - effects on the phenotype, i.e. they intensify or reduce it.
What kind of distribution does continuous data fall under?
Normal.
What does VP = VG + VE mean?
Phenotypic variation is the sum of genetic and environmental variation.
VG is itself a product of 3 entities. What are they?
VP = VA + VD + VI
VA = additive variance VD = dominance variance VI = interaction variance
Thus the fully expanded version of VP = VG + VE is?
VP = VA + VD + VI + VE
Define VA.
Additive variance: alleles have heritable additive effects.
What do we expect heterozygotes to look like if variance is additive?
The phenotype will be midway between the two homozygous phenotypes for that locus.
VA is a function of 2 parameters. What are they?
- Average effect
2. Breeding value
Define average effect.
Refers to the average effect of an allele at a single locus.
‘The mean deviation from the population mean of individuals which received that allele from one parent’
Define breeding value.
The summation of the average effect of all alleles at all loci.
Why does additive variance cause relatives to resemble each other?
Alleles are transmitted faithfully from parents to offspring.
Define VD.
Dominance variance: phenotypic differences caused by INTRA-locus competition of alleles, i.e. in heterozygotes the recessive is masked by the dominant allele.
Define VI.
Interaction variance: also called epistasis variance. Genotypic differences caused by INTER-locus competition of alleles, i.e. some loci will silence others.
VD and VI are dependent on other alleles that are present in the genotype, thus the effect varies between generations. True or false?
True - meiosis changes the combinations of alleles in the genome between relatives.
Define heritability.
The proportion of genetic variance that is solely additive.
What is heritability a good marker of?
Relatedness, alleles are conserved from parents to offspring.
How do you calculate heritability?
VA/ VP
Heritability can be generalised. True or false?
False - heritability is specific to each population and their environment.
