Upload
vutuyen
View
225
Download
2
Embed Size (px)
Citation preview
10.3 Gene pools and speciation (AHL)
Essential idea: Gene pools change over time.
The two butterfly species of the Heliconius genus above have only recently diverged and consequently differ in twelve regions of their genomes. Other species of the genus diverged earlier show hundreds of genomic changes.http://phys.org/news/2013-10-evolution-species-requires-genetic.html
By Chris Paine
https://bioknowledgy.weebly.com/
Heliconius pachinus Heliconius cydno
photos from http://www.heliconius.net
Understandings, Applications and SkillsStatement Guidance
10.3.U1 A gene pool consists of all the genes and their
different alleles, present in an interbreeding
population.
10.3.U2 Evolution requires that allele frequencies change
with time in populations.
10.3.U3 Reproductive isolation of populations can be
temporal, behavioural or geographic.
10.3.U4 Speciation due to divergence of isolated
populations can be gradual.
10.3.U5 Speciation can occur abruptly. Punctuated equilibrium implies long periods
without appreciable change and short periods
of rapid evolution.
10.3.A1 Identifying examples of directional, stabilizing and
disruptive selection.
10.3.A2 Speciation in the genus Allium by polyploidy.
10.3.S1 Comparison of allele frequencies of geographically
isolated populations.
http://www.flickr.com/photos/limowreck666/171979083/
allele frequencyAllele frequency is the proportion of all copies of a gene that is made up of a particular gene variant (allele).
gene poolThe total collection of different alleles in an interbreeding population.
ExampleSay if a recessive allele h made up
2% of the total in a human population…
…then the dominant allele Hwould make up 98%.
The frequency for h would be expressed as 0.02 and for H 0.98Recessive allele frequency + dominant allele frequency = 1
(for characteristics determined by two alleles)
10.3.U1 A gene pool consists of all the genes and their different alleles, present in an interbreeding population.
New combinations of alleles lead to new phenotypes that can then be selected for or against by the environment.
This leads to evolutionary change in the species
10.3.U2 Evolution requires that allele frequencies change with time in populations.
10.3.A1 Identifying examples of directional, stabilizing and disruptive selection.
Freq
uen
cy o
f in
div
idu
als
Phenotype (fur colour)
Freq
ue
ncy
of
ind
ivid
ual
s
Phenotype (fur colour)
Freq
ue
ncy
of
ind
ivid
ual
s
Phenotype (fur colour)
Freq
ue
ncy
of
ind
ivid
ual
s
Phenotype (fur colour)
Directional, stabilizing & disruptive selection
Disruptive selection
Directional selection
Stabilizing selection
Rabbit image: http://cliparts.co
KeyEvolved populationOriginal populationSelective pressure
Original population If the selective pressures applied to a population do not change then the population will not evolve.
However if the selective pressures do change then the population will evolve, but how it evolves dependson which phenotypes are experience the greatest pressure.
Medium ground finch Beak shape and size in Geospiza fortis
http://commons.wikimedia.org/wiki/File:Geospiza_fortis.jpg
10.3.A1 Identifying examples of directional, stabilizing and disruptive selection.Fr
eq
ue
ncy
of
ind
ivid
ual
s
Phenotype (fur colour)
Directional selection KeyEvolved populationOriginal populationSelective pressure
Selective pressure: during dry years small seeds are not adundant.Result: Birds with larger tougher beaks become more frequent
Example from 5.2.A1 Changes in beaks of finches on Daphne Major.
10.3.A1 Identifying examples of directional, stabilizing and disruptive selection.
Stabilizing selectionFr
equ
en
cy o
f in
div
idu
als
Phenotype (fur colour)
KeyEvolved populationOriginal populationSelective pressure
Selective pressures: Babies of low weight lose heat more quickly and get ill from infectious diseases more easily. Babies of large body weight are more difficult to deliver through the pelvis.Result: Medium weight babies have a much lower mortality and hence the frequency of medium weight babies increases.
Human birth weight
Mayumi Paine (aged 1 day) – photo by Chris Paine
10.3.A1 Identifying examples of directional, stabilizing and disruptive selection.
Disruptive selectionFr
equ
en
cy o
f in
div
idu
als
Phenotype (fur colour)
KeyEvolved populationOriginal populationSelective pressure
Grass (Anthoxanthum odoratum)
Selective pressure: soil close to mine workings contaminated with metals, e.g. copper.Result: Two distinct grass populations arise; slower growing metal-tolerant and faster growing non-tolerant populations.
https://commons.wikimedia.org/wiki/File:20150628Anthoxanthum_odoratum3.jpg
The circumstances preventing different species from interbreeding are known as reproductive isolating mechanisms
10.3.U3 Reproductive isolation of populations can be temporal, behavioural or geographic.
https://youtu.be/rlfNvoyijmo
Your syllabus focuses on three ways in which populations can be isolated to prevent reproduction:• Temporal – timing• Behavourial (this affects only animals)• Geographic
*This video also looks at other aspects of the topic including polyploidy, but remember it is not an IB course specific resource so make sure that you know what is relevant to you.
The reproductive isolation only promotes selection in sexually reproducing organisms: it doesn’t apply to single-celled organisms.
Rats!
http://www.flickr.com/photos/microagua/3721497804/
10.3.U3 Reproductive isolation of populations can be temporal, behavioural or geographic.
Temporal isolation
J F M A M J J A S O N D
MAXPinus radiata (Monterey Pine)Pinus attenuata (Knobcone pine)
Polle
n P
rod
uct
ion
Pinus radiata and Pinus attenuata are prevented from hybridising because they have separate pollination times.They can be made to hybridise by pollinating them manually.
http://www.flickr.com/photos/alancleaver/4293345631/
*Random fact: The Monterey pine is at risk in it’s native range but is one of the most common plantation trees in the world. If you see a pine forest in Australia or NZ, it is probably Pinus radiata
Month
10.3.U3 Reproductive isolation of populations can be temporal, behavioural or geographic.
Ecological isolation
The two species are in the same area, but live in different habitats
http://www.flickr.com/photos/annetanne/3035068940/ http://www.flickr.com/photos/carinemily/644052381/
I love me some
CaCO3 in my soil
Blechhh!Acidic soils
are more my thing
Viola arvensis Viola tricolor
10.3.U3 Reproductive isolation of populations can be temporal, behavioural or geographic.
Behavioural isolation
Animals exhibit courting behaviour (song, dance etc.) or release pheremones to
attract mates. Individuals are only attracted to, and will only mate with,
members of the opposite sex who perform the appropriate ritual or release the
correct chemical.
Yo! I don’t like your music!
Its like, totally
mutual!
http://www.flickr.com/photos/rowelbg/2895578034/http://www.flickr.com/photos/nrk-p3/2333221093/
10.3.U3 Reproductive isolation of populations can be temporal, behavioural or geographic.
http://www.pbs.org/wgbh/evolution/library/05/2/swf_pop/l_052_01.html
10.3.S1 Comparison of allele frequencies of geographically isolated populations.
PanI is a gene in cod fish that codes for an integral membrane protein called pantophysin.
Two alleles of the gene, PanIA and PanIB, code for versions of pantophysin.
Samples of cod fish were collected from 23 populations in the north Atlantic and tested to find the proportions of the alleles in each population.
The proportions of alleles in a population are called the allele frequencies. The frequency can vary from 0.0 to 1.0 with the total frequency of all alleles always being 1.0.
Comparison of allele frequencies
Key
12
PanIA PanIB
Population #
Use the information and charts to answer the questions on the following slides…
Source: RAJ Case et al. 2005. “Macro- and micro-geographic variation in pantophysin (PanI) allele frequencies in NE Atlantic cod Gadus morhua.” MEPS. Vol 301. Pp 267–278. Figs 1 and 3.
10.3.S1 Comparison of allele frequencies of geographically isolated populations.
Comparison of allele frequencies
Key
12
PanIA PanIB
Population #
1. State the two populations with the highest PanIB allele frequencies. [1]
1. State the population in which the allele frequencies were closest to 0.5. [1]
1. Deduce the allele frequencies of a population in which half of the cod fish had the genotype PanIA PanIA, and half had the genotype PanIA PanIB. [2]
Graph and questions from IB Questionbank
10.3.S1 Comparison of allele frequencies of geographically isolated populations.
Comparison of allele frequencies
Key
12
PanIA PanIB
Population #
1. State the two populations with the highest PanIB allele frequencies. [1]
1 and 2
1. State the population in which the allele frequencies were closest to 0.5. [1]
7/11
1. Deduce the allele frequencies of a population in which half of the cod fish had the genotype PanIA PanIA, and half had the genotype PanIA PanIB. [2]
PanIA 0.75 and PanIB 0.25
Graph and questions from IB Questionbank
10.3.S1 Comparison of allele frequencies of geographically isolated populations.
Comparison of allele frequencies
Key
12
PanIA PanIB
Population #
4. Identify an example of two geographically isolated populations. [1]
5. Give Suggestions why the PanIB allele is more common in population 13 than population 22. [2]
Graph and questions from IB Questionbank
10.3.S1 Comparison of allele frequencies of geographically isolated populations.
Comparison of allele frequencies
Key
12
PanIA PanIB
Population #
4. Identify an example of two geographically isolated populations. [1]
any population from 14 – 23 and any population from 1 – 4
5. Give Suggestions why the PanIB allele is more common in population 13 than population 22. [2]
Cooler water temperature favoursPanIB;Interbreeding with icelandic/more northern populations;
Graph and questions from IB Questionbank
10.3.U4 Speciation due to divergence of isolated populations can be gradual. AND 10.3.U5 Speciation can occur abruptly.
http://www.ib.bioninja.com.au/_Media/pace_of_evolution_med.jpeg
Phyletic Gradualism• Evolution occurs at a constant pace
over a long period of time (due to the accumulation of mutations).
• For example the change in size and hoof of the modern horse.
Punctuated Equilibrium• Long periods of stability are interrupted
by ‘During rapid’ evolutionary changes.• periods of stability well-suited organisms
have no reason to evolve until large environmental changes (e.g. meteor strikes) cause selection pressures to shift.
• Gaps in the fossil record show mass extinction events.
The rate of speciation varies
Gradualism is the older idea. Darwin is one of the
originators of the concept, borrowing from his friend
Charles Lyell. Darwin recognised however that not all species evolve at the same rate all of the time
"I think case must be that one generation should have as many living as now. To do this and to have as many species in same genus (as is) requires extinction . Thus between A + B the immense gap of relation. C + B the finest gradation. B+D rather greater distinction. Thus genera would be formed. Bearing relation" (next page begins) "to ancient types with several extinct forms"
http://commons.wikimedia.org/wiki/File:Darwin_tree.png
10.3.U4 Speciation due to divergence of isolated populations can be gradual.
Punctuated equilibrium was first proposed by palaeontologists Niles Eldredge andStephen Jay Gould in 1972. They were the first to suggest that species did not change for long periods of time but were in stasis until events punctuated (disrupted) the equilibrium (balance)
Richard Dawkins is a prominent critic of the theory
TOK - Find out more: • What evidence are the two theories based on?• Gould (deceased) and Dawkins have both become
popular writers. How does this affect the weight of their opinion:• In the scientific community?• In the wider community?
http://www.flickr.com/photos/mrccos/288136783/sizes/m/in/photostream/
http://www.flickr.com/photos/ideonexus/4022727065/
10.3.U5 Speciation can occur abruptly.
So far you’ve learnt that cells contain two homologous sets of chromosomes.Well….. that isn’t always the case.
It goes on:PentaploidHexaploidSeptaploidOctaploidEtc.up to:
84-ploid and 1260 chromosomes
Ophioglossum reticulatumA small fern.
The incredible thing is that this plant is able to carry out meiosis accurately with
1260 chromosomes to divvy up
http://commons.wikimedia.org/wiki/File:Haploid,_diploid_,triploid_and_tetraploid.svg
Nature of science: Looking for patterns, trends and discrepancies - patterns of chromosome number in some genera can be explained by speciation due to polyploidy. (3.1)
Edited from: http://www.slideshare.net/jasondenys/ib-biology-option-d2-species-and-speciation
How polyploidy happens
When non-disjunctionoccurs during meiosis in humans, an individual can end up with an extra chromosome or missing chromosomes (e.g. An extra chromosome 21 means Downs syndrome).
Total non-disjunction, is when one of the two cells produced during Meiosis I gets all of the chromosomes. The other cell is not viable and is reabsorbed.This results in two (2n) daughter cells from meiosis instead of the usual four (n) daughter cells.
Nature of science: Looking for patterns, trends and discrepancies—patterns of chromosome number in some genera can be explained by speciation due to polyploidy. (3.1)
http://www.ib.bioninja.com.au/_Media/polyploidy_med.jpeg
Polyploidy is much more common in plant species - they lack separate sexes and are capable of asexual reproduction (self-pollination)
Tetraploid offspring cannot mate with diploidorganisms (triploid offspring tend to be infertile), speciation has occurred
Edited from: http://www.slideshare.net/jasondenys/ib-biology-option-d2-species-and-speciation
There exist few polyploid animals species (examples include salamanders, goldfish and salmon).
Polyploidy often leads to increased size, resistance to disease and overall vigour.
However, polyploidy is a great source of speciation amongst plants.
https://youtu.be/6Jjilc5eqS0
Nature of science: Looking for patterns, trends and discrepancies—patterns of chromosome number in some genera can be explained by speciation due to polyploidy. (3.1)
Many agricultural plants are polyploid(e.g. wheat) due to having bigger fruits, seeds and storage organs
Polyploidy in animals and plants
https://commons.wikimedia.org/wiki/File:Wheat_close-up.JPG
Edited from: http://www.slideshare.net/jasondenys/ib-biology-option-d2-species-and-speciation
10.3.A2 Speciation in the genus Allium by polyploidy.
Chromosome number in genus Allium
https://commons.wikimedia.org/wiki/File:Starr_070313-5652_Allium_cepa.jpg
Onion (A. Cepa), 16 Chromsomes
https://commons.wikimedia.org/wiki/File:Poireaux_artlibre_jnl.jpg
English Leek (A. Cepa), 32 Chromosomes
Many species of this genus commonly reproduce asexually and if polyploidy confers an advantage a new species may arise.
Bibliography / Acknowledgments
Bob Smullen
Jason de Nys