Quantitative Genetics I & II Flashcards
What is Mendelian variation
genetic variation among members of a family, or within-family variance
What is continuous variation
characteristics like weight or height, which change gradually
How can Mendelian loci create continuous variation?
when multiple genes (loci) at different locations on chromosomes all contribute to a single trait
Compare and contrast the Biometricians vs. the Mendelians. What scientists united these two schools of thought (using theory & experiments)?
Biometricians: saw heritable variation as continuous, existed before 1900, maintained that Darwin’s idea of slight differences among individuals was the essence of evolution, most naturalists and systematists belonged to this school, initiated by Darwin’s cousin, Francis Galton
Mendelians: mostly laboratory geneticists, viewed variation as discrete and sudden, not continuous, most laboratory geneticists did not believe in evolution by natural selection: too slow and required subtle variation, some even dismissed continuous variation as heritable at all
Understand how East’s experiment showed that continous variation in traits can be formed from Mendelian genetics
-crossed short & long flowered plants
-produced F1s and F2s
-logic: if continuous variation is composed of discrete units, the original phenotype should be recoverable
-East recovered parental phenotypes by artificial selection in about 3 generations
What is variance? What does it measure? Be able to calculate a variance if given the equation. What does it mean to have high or low variance?
quantifies the width of the distribution
Describe the variables in this sentence: VP = VG + VE
VP (total phenotypic variance) = VG (genetic variance) + VE (environmental variance)
-VP is the total statistical variance for the trait in the population and can be statistically calculated from population data
What is a phenotypic value?
Phenotypic value is calculated from the genotypic values for each individual for each trait. Each individual’s phenotypic value is calculated from its genotypic value with an environmental effect determined by the heritability h^2
What are the three kinds of genetic variation? Which form of genetic variation is responsible for the similarity in phenotype between parents and offspring?
- Additive genetic variance, VA: When the phenotypic value for a heterozygote is exactly intermediate between both homozygotes, the characters are said to be “additive”. Additive genetic variance is almost completely responsible for heritable genetic variation.
- Dominance variance, VD: When the phenotypic value deviates from additivity, this is called Dominance Variance, and it is due to interactions among alleles. Dominance effects are not transmitted directly from parent to offspring because only one allele is contributed by each parent.
- Epistatic Variance, VI:This is genetic variation due to interactions among loci. This is not heritable variance because interactions among loci can’t be passed on to offspring due to independent assortment.
Describe epistasis. If given a table as was given in lecture for wing length in the butterfly Danaus chryssipus, be able to spot obvious epistasis.
The effect of the interaction between two or more loci on the phenotype whereby their joint effects differ from the sum of the loci take separately
Butterfly example:
-mean forewing lengths (mm) of female butterflies of differing genotypes at two loci
-B is dominant over b
-need to know both loci to predict the influence of an allele on the phenotype
What is environmental variance? Does the environment influence the phenotype?
Differences among individuals in a population that are due to differences in the environments they have experienced. Yes, environmental effects cause environmental variance. This is variation in phenotypic values that is based on environmental factors, such as temperature, food, etc.
What is a maternal effect? Understand the snail coiling example
This is an effect of the mother on phenotypic values for non-genetic reasons, such as egg nutrition levels, egg hormones, transmission of symbionts (such as chloroplast or mtDNA) to offspring, maternal gene products, etc
Snail coiling example:
-in many organisms, the first few cell divisions are entirely controlled by maternal gene products.
-genes in the zygote are expressed after the cells divide a few times
-D dominant
-D coils right
-d coils left
What are environmental effects
This is variation in Phenotypic Values that is based on environmental factors, such as temperature, food, etc.
What is maternal effects
This is the effect of the mother on phenotypic values for non-genetic reasons, such as egg nutrition levels, egg hormones, transmission of symbionts (such as chloroplast or mtDNA) to offspring, maternal gene products, etc.
What is developmental noise
Variation due to random events in development even under the same conditions - for example, you are not completely symmetrical, even though your right and left side have shared the same genotype and environment
What is broad sense heritability
the fraction of phenotypic variation within a population that is due to genetic variation
What is narrow sense heritability
the fraction of phenotypic variation within a population that is due to additive genetic variation (i.e., heritable genetic variation)
