Seeds in basic soil make pink flowers and seeds planted in acidic soil turn into blue flowers
You observe a population of birds that are genetically identical regarding alleles for height. Height differences are the result only of environmental effects
Taller stature would be beneficial for feeding on taller plants. Can this population evolve by natural selection?
No, they all have the same genes and alleles, so they can't evolve
Can migratory behavior be determined by genes, the environment, or both?
Predispositions for migration and time-and-direction compass are genetically controlled can be both.
Song birds: fledglings complete autumn migration independent of their parents (everything is genetic)
Waterfowl: genetic control of predisposition for migration phenotype BUT migratory route is learned (environmental control of phenotype)
Distinguishing genetic vs. environmental effects on phenotype?
Wolf example: Pack A is better at hunting.
You can change the environment to determine if the hunting phenotype is genetic or environmental.
Use a cross fostering experiment
Cross fostering experiment
You break up the litters at birth and randomly redistribute the young among family groups
You then assess the hunting prowess phenotype of cross fostered pups at adulthood
What would happen if the hunting prowess was genetic effect? environmental effect?
Genetic effect- pack A pups always have a high hunting prowess no matter the pack that raises them and vise versa
Environmental effect- pack A pups have low hunting prowess when raised in pack B, vice versa
What goes on the axises when drawing a graph?
X-axis: is the independent variable (pack of origin (genes) and the pack the pups are raised in (environment)
Y-axis: the dependent variable (number of successful kills/attempts)
Which graph supports the hunting prowess phenotype as genetic vs. environmental behavior (learned) hypothesis?
B) 2 supports environmental hypothesis, 2 supports genetic
If the results from the wolves were genes what would you suggest? What would you suggest if they were environmental?
If the hunting prowess was genetic then you should cross breed
If the hunting prowess was environmental then you would have pup Bs live within pack A
What do these results indicate?
There is both genetic and environmental variation are important in hunting prowess phenotype variation between populations.
Evolution by natural selection can act only on heritable characteristics.
You need to differentiate the effects of environmental vs. genetic variation on phenotypic variation for evolution.
Phenotypic Variation due to Genotypic Variation (Vg)
The phenotypic variation is due directly from genes.
Phenotypic Variation due to Environmental Variation (Ve)
Even if the genes are the same, the phenotypic variation is from the environment.
Total phenotypic variation (Vp)
Total phenotypic variation due to both genetic variation and environmental variation
As long as some phenotypes look different then Vp>0
Would a population evolve if everyone in the population had heterozygous alleles?
Natural selection occurs if the beneficial characteristics get passed down.
If everyone had heterozygous alleles then the parent generation would not evolve, however the children would have variation.
Vg is lowest in which of the following populations?
C) Population 2
Vg is highest in which of the following populations?
A) Equally high in two of the populations
Ve is lowest in which of the following populations?
B) Population 4
Vp>0 in which of the following populations?
D) All of the populations
Vp is the highest in which of the following populations?
E) Population 3
Which of these populations could evolve by natural selection for color phenotype?
E) More than one of the populations, but not all
Quantifying phenotypic variation
Vp= Vg + Ve
Vp- phenotypic variationVg- genotypic variation
Ve- environmental variation
For example: height is a result of genotypic and phenotypic variation
What type of phenotypic variation does natural selection act on?
Natural selection
Heritability (h2)
The proportion of phenotypic variation in a population attributable to genotypic variation
Determines how strongly a character in a population can respond to natural selection
What does it mean when heritability=1 (h2=1)
Completely heritability-> all phenotypic variation is due to genotypic variation
Heritability is high when phenotypic variation due to environmental variation is low
Is it possible for a character to vary in population and have a heritability of 0?
Yes, all of the variation would be due to environmental variation
Can one population of a species have h2=0 for a specific phenotype but in another population have h2=0.4 for that same phenotype?
Yes because different gene pools reside in different populations and there are different environmental effects between populations
All individuals in a population have the exact same allele that codes for a given phenotypic characteristic, Ve=0 for this trait in this population.
Given this information what does h2 equal in this population?
B) 0 because there is no genetic variation in the population therefore, no phenotypic variation can be explained by genotypic variation because there is none
Acorns and herbivory example:
Two populations of red oaks under identical selective pressure from herbivores
Oaks vary in acorn tannin (bitter tasting compounds in acorns) concentration phenotype.
h2=0.5 in population 1, h2=0.2 in population 2
After many generations of identical herbivory selective pressures, which of the following do you predict will occur?
A) Both populations of oaks will show increases in average acorn tannin concentrations, but the increase will be greater in population 1 than population 2
In population 1, most of the variation is genetic so the potential for variation is greater
Assume h2=0.8 for human height in our class. Which of the following is accurate given this heritability?
B) 80% of the variation in height in this class is explained by genetic variation
Heritability is determined by the proportion of phenotypic variation in a population. Individuals cannot vary genotypically
Epigenetic inheritance
Inheritance of traits transmitted in ways other than DNA
Turning on/off genes, enhancing/diminishing gene expression with NO change in the DNA sequence.
--i.e. addition of methyl group to DNA prevents expression of genes
Organisms with identical DNA may express different phenotypes because of different epigenetic expression
Epigenetic's and the environment
Environmental factors may change epigenetic's of an individual and therefore change their phenotypes
Case study of rats:
Loving rat moms change their babies' gene expression.
Low nurturing mom: anxious, high stress response, don't lick babies much (offspring=high stress)
High nurturing mom: relaxed, low stress response, lots of baby liking (offspring=low stress)
How to determine if it is genetic or environmental?
Do a cross foster experiment and see how the offspring react
Scientists hypothesized that childhood environment affects epigenetics of GR gene
GR gene
Produces protein that binds stress hormone cortisol
Allows rapid recovery from stress when active
More methyl groups on GR gene, GR not expressed= slower stress recovery, more anxious
Fewer methyl groups on GR gene expressed= faster stress recovery, less anxious
What happens when you add methyl groups to nurturing rats? Injecting non-nurturing rats with a drug that removes methyl groups?
Nurtured rats became high stress and non-nurtured rats became low stress.
Maternal licking releases chemical that removes methyls groups from GR gene
What environmental situation would high anxiety and stress responses be beneficial for survival and reproduction?
Low food resources
High predator pressure
How might an epigenetic response to these environmental pressures be more beneficial than an evolutionary response?
Much faster-- doesn't require many generations
Can change the survival/reproduction success of an individual that already exists -> evolution can't do this.
