Exam 2 CH 8-13 Flashcards
(22 cards)
What is a cline?
Geographic variation in a character
Describe the cline?
Why is there not a smooth cline for plants that do not produce cyanide?
Some plants produce CN to protect themselves from herbivores
At 0ºC cline - to the east lower temp whereas at the ocean is a warmer/higher temp
The genes needed to produce cyanide have been deleted in cold climates
-Reason: The cold can break up the vacuoles containing CN and die
What is the difference between a large cline and a small cline?
Large - hundreds or thousands of km long
ex: mass size in moose by lattitude
Small - dozens of meters
- local adaptation
ex: grass (common bent) grows on and around an abandoned surface mine in Wales
What is gene flow?
Mixing of alleles from different populations
What are the effects of gene flow?
- Introduces new alleles into a population from other populations (dispersal)
- Equalizes allele frequencies (decreases genetic variation between populations)
How do we measure gene flow (migration)?
(m)
Difference in an allele’s frequency before and after migration in a given population:
(Difference)p = m (pm - p)
What is migration rate?
Used to quantify gene flow among discrete patches
-how quickly gene flow erodes genetic differences between populations
(equalizes)
-
Chapter 8 – Suppose that in generation 0, the frequency of allele A1 in a population of armadillos is 0.4. In each generation, 10 percent of the individuals in that population are migrants from another population that has an allele frequency of 0.6.
- Calculate the frequency of A1 in each of the next two generations (generations 1 and 2). Hint: Use equation 8.1.
- Is the change in allele frequency in generation 2 greater than, less than, or equal to the change in generation 1? How can you explain that answer?
- What will the allele frequency become in this population after many generations?
- Δp = m (pm – p)
- The change in allele frequency in generation 2 is less than to the change in generation 1. To calculate, take the differ ence in the total population with the migrants and the focal population before migration.
Generation 2 (0.438 - 0.42) = 0.018
Generation 1 (0.42 - 0.4) = 0.02
The reason to why generation 2 has a way lower allele frequency than generation 1 is due to gene flow. In generation 1 there was the introduction of new alleles into the population, following the next generation, the allele frequencies are beginning to equalize (i.e. it decreases the genetic variation between population).
- From the follow up with part b, it was already shown that the allele frequency was beginning to decrease. If migration continues, and goes on for several generation, the allele frequency in this population will eventually equal to the migrants. The reasoning behind is with each migration (the exchange of alleles) it eventually erodes the genetic differences between the two populations and the genetic variation between the two species is at a way lower effect.
How do we measure gene flow with spatially continuous populations?
Migration variance σm2
What would be the significance of migration variance?
(square root)
Showing the average movement per generation
How to measure genetic divergence between populations?
Measures the fraction of total genetic variance found across two or more populations that results from genetic differences between them
Fst
What would a Fst of 0 or 1 mean?
0 = populations are genetically identical
1 = populations are fixed for a different allele
What does this phrase mean?
“The striking phenotypic differences we see among human populations are not representative of the genome as a whole.”
Simple measures of genetic similarity cannot be used to determine which populations do and do not belong to the same species
How do we differentiate different populations?
Example: Controlled experiment of the yarrow plant
Differences between populations can be caused by phenotypic plasticity as well as by genetic divergence
-There was some genetic variation between them, but not enough genetic diversity to call it a different species
What happens when selection is favored in the prescence of gene flow?
Increase tension between these two evolutionary forces
- enhances the genetic differences between populations
- then erosion by gene flow
What would be the two effects with/without gene flow and selection (genetic drift as well)?
0 gene flow = selection on alleles with highest fitness at any place to become fixed
0 selection (or genetic drift) = gene flow would make allele frequencies equal everywhere
What is the relationship between gene flow and drift?
High gene flow = genetically very similar
Low gene flow = 2 populations will have very different allele frequencies
Describe the figure and explain the effects?
Even though dispersal can lead to extinction
- there is high genotype for dispersal
- advantage in having dispersal even though it might put individuals in danger
What are the factors in dispersal?
- Find better habitat
- Competition with relatives (reject their seeds from parents or grow fleshy fruit around the seed)
- Decrease the risk of inbreeding
How might benefits offset by costs in the evolution of dispersal?
Good patches vs landing on cement
*Dispersal can cause evolutionary change even without the help of natural selection
Describe what is happening?
A –> B
C –> D
E –> F
A –> B
A (original population) at a latitude (shift in temperature) –> B (shift) in newly suitable envirnoments
*some mortality, may not have the right genotype to adapt
C –> D
C block from dispersal (inhabitable area, not equipped to live on a mountain)
E –> F
E limited dispersal ability - could adapt if have the right set of fitness with the genes to move to higher elevation
