Topic 5 - Fundamentals of Evolution : Drift and Speciation

Question 1

Drift explanation - spandals of San Marco

Answer 1

Architects wanted arches on a rectangular space
These created triangular spaces between the arches and the rectangles
These were evnetally used as sapce for paintings
Did they need space for paintings so the made spandals or did they need arches and spandals were a bi-product?

It was the bi-product!

Same with t rex small arms. Dd evolution make the small arms for a purpose or did it create large legs and a head and so the arms grew smaller to accomodate these and not fall over.

Not all evolution is selection, sometimes it is other things

Question 2

Genetic Drift

Answer 2

Evolution by chance

Question 3

Hardy-Weinburg equilibrium

Answer 3

Used to predict what the frequency of genotype will be in the next generation

G is a gene of interest
2 alelles G and g
veryone has 2 alleles
DIfferent combos give different phenotypes

       G (p)         g(q)       female

G(p) GG Gg

g(q) Gg gg

Male

Question 4

Equation

Answer 4

G (p) 50% g(q) .5 female

G(p)    GG            Gg
.5
g(q)     Gg             gg
.5
Male

p2 + 2pq + q2=1

pxp= .5 x .5 = .25 25% are GG
2(pxq)= 2x (.5 x .5) = .5 50% are Gg
qxq - .5x.5 =.25 25% are qq

Assuming assumptions hold, this is what you would expect in the next generation

Question 5

Hardy-Weinberg equilibrium assumptions (5 things)

Answer 5

1) No mutation
2) No selection
3) No genetic drift
4) No gene flow (immigration)
5) Random mating (no sexual selection)

ie NO evolutionary change

Question 6

Why calculate hardy-weinberg equilibrium?

Answer 6

Allows us to study evolution

You can compare the predicted frequency with the actual frequency to determine whether the popultion is evolving

ALso used in medicine to estimate the f of carriers (heterozygotes) for recessive diseases.

Question 7

EARTHQUAKE!!! (example)

Answer 7

8 individuals, 2 alleles each
f of G = .5
f of g =.5

2xGG
4xGg
2xgg

id 1x Gg and the two gg died, 10 alleles left.
2 GG
3Gg
0gg

Counting them: 10 G and 3 g
f of G = .7
f of g = .3

p2+2pq+q2=1

p2 = .7X.7 = .49 so 50% GG
2pg = 2x(.7x.3)=.42 thus 40% are Gg
q2 + .3x.3 = .0.9 so 10% are gg

This happened by chance. The earthquake did not select them. Tis is the idea behind genetic drift.

Question 8

Key points for genetic drift

Answer 8

1) effects are random

2) effects are larger in small populations sp they change faster

Question 9

Two ways genetic drift can result in big changes: 1 - Genetic Bottleneck

Answer 9

An extreme example of genetic drift where an event leads to a big decrease in population size and genetic diversity.

eg a flood where only a few survive, taken at random and y chance (they did not have a survival advantage)

The new population will descend only from this small number of individuals (with their small amount of genetic diversity)

Question 10

Two ways genetic drift can result in big changes: 1 - Founder effect

Answer 10

A few individuals found a new population somewhere new

eg lizard moves to a new island by chance. All populations are now descended from this founder

There is less genetic diversity and less variation for selection to act on BUT the small population means genetic drift can have a big effect.

Eg lizards move to new island. Random mutation causes bigger claws, descendants climb trees and do well cos its only them up there. Beach lizards random mutation makes them yellow and this protect them from predation

After millions of years, the populations of lizards on the island (descended from the founder that moved there) are totally different from the population on the mainland

Question 11

A species is

Answer 11

a population whos members can produce offspring that are

(1) viable - survive after birth
(2) fertile - they can reproduce

Question 12

Reproductive isolation

Answer 12

mechanisms that prevent gene flow between members of a different species\2 types

pre-zygotic or post zygotic

zygote formed by the fusion of to gametes

Question 13

Pre-zygotic isolation (5 types)

Answer 13

1 - habitat isolation - ltwo species live in a different environment and never meet

2 - Temporal isolation - related species breed at different times of the year so never cross breed

3 - Behavioural isolation - different mating activities, males of one species are not attractive to the other

4 - Mechanical isolation - a mechanical mechanism that prevents cross breeding (eg flowers whos pollinator species cannot fit into to the other one)

5 - Genetic isolation - gametes cannot unite

Question 14

Post - zygotic isolation (2 types)

Answer 14

Hybrid inviability - gametes unite but viable offspring cannot form

Hybrid infertility - gametes unite but offspring is infertile (mule)

Question 15

Why is pre-zygotic more common than post zygotic?

Answer 15

Mating is costly:
Finding and attracting a mate takes time and energy
Producing eggs and offspring also takes time and energy

Individuals who mate outside their species produce fewer offspring and their alleles will be less represented in the next generation

Thus selection should favour those individuals who are better at identifying and mating with conspecifics (members of their own species)

Question 16

Allopatric Speciation

Answer 16

Is when there is physical isolation

AN example of this is finches on islands that were hysically isolated and hence, adapted to their environment with beak size. In addition to eating, beaks are used for mating (attracting females).

Closed beaks make longer vocal tracts and hence, deeper sounds. Open beaks make shorter vocal tracts and higher pitched sounds.

Big beaks make simple, slow sounds as they’re harder to move. Smaller beaks make rapid, complex sounds as easy to move.

Over time these distinct sounds became desirable for members of that species.

Different species have different beak sizes which over time have attracted the females of that species. It acts as a pre-zygotic mechanism. Females may also have responded better to specific sounds thus sexually selecting those sounds. With time, they only mate with those species.