Task 3 GENES AND NATURAL SELECTION IN POPULATIONS

Question 1

Purifying selection

Answer 1

occurs when an allele that does something useful is fixed at a locus. Whenever a mutation occurs at this locus it will decrease the fitness and gets weeded out
o Variation reducing

Question 2

Stabilizing selection

Answer 2

describes selection where current population average contains the optimum fitness. Individuals higher or lower in this trait have reduced fitness
o When a population lives in the same environment for a time there will be stabilizing selection

Question 3

Directional selection

Answer 3

Occurs when optimum of fitness is not the average of the population. Phenotypes that differ in the right direction are according to this higher in fitness
o Produces mutations in the favourable genotype in the long run. And accounts for change

Question 4

Disruptive selection

Answer 4

When there is no medium and both high and low extremes are favoured

Question 5

Heterozygotes advantage

Answer 5

describes the situations where individuals with one copy have a higher fitness than individuals with no or two copies of an allele
o ß-globin gene: When Homozygote it can lead to strokes because of changes in blood cells, When heterozygotes these risks are smaller but it still has the beneficial effect of being more resistant to malaria

Question 6

Negative frequency-dependent selection

Answer 6

the situation where the phenotype is high in fitness when it is rare but not when it is common. The result is that it will stabilize at an intermediate frequency

Question 7

Force of mutation

Answer 7

genetic variation will persist if the force of mutation is strengthened or that of selection weakened
o For polygenic characteristics, the effective strength of mutation is proportional to the number of genes involved, b.c. each gene has the possibility of mutation

Question 8

Inconsistent selection

Answer 8

variation might persist when selection is inconsistent

o Occurs when the selective optimum changes in an environment (Darwins finches)

Question 9

Sexually antagonistic selection

Answer 9

The selection optimum might not be the same for males and females. E.g. height (because costs more energy to be tall)
o So when a male with high fitness gets a female child it might be low in fitness
o Leads to more variety

Question 10

Adaptionist hypothesis

Answer 10

if some features or behaviour is commonly found in a species it means that it is probably an efficient design which was the solution for a problem which the species faced

Question 11

Ultimate explanation

Answer 11

the explanation how the that particular design increased in ancestral fitness

Question 12

Proximate explanation

Answer 12

the account of the genetic features that led to the formation of that characteristic

Question 13

Human sickle disease

Answer 13

The case of the malaria protecting gene, changes the blood structure so that it is less effective in transporting oxygen or fighting disease

Question 14

Exponential growth

Answer 14

the exponential growth of a population without selection

Question 15

Reproductive success

Answer 15

Determined by the number of viable descendants produced

Question 16

Fitness

Answer 16

determined by the number of copies of an allele in the next generation. When there are two alleles the fitness is determined by the proportion of both

Question 17

Time lags

Answer 17

There is a time lag between the optimal phenotype and the actual population because it will always take several generations to reach the optimal state

Question 18

Selective regime

Answer 18

Environment changes and so the optimal phenotype does

o Phenotypic plasticity: the ability of the phenotype to respond to changes within one generation

Question 19

Genetic correlations

Answer 19

the situation between two traits in which selecting for the one traits effects the other as well (pleiotropy and linkage)

Question 20

Hitch-hiking traits in fox domestication

Answer 20

They took foxes and after 30-35 generations they were responsive to humans. Other characteristics changed as well despite they were only aiming for tameness

Question 21

Trade-offs in groupies

Answer 21

arises when two traits have opposite effects on fitness but are genetically correlated with each other.

Question 22

Shape of adaptive landscape

Answer 22

Some changes that might lead to progression in the long run have to reduce fitness first, so they won’t have the chance to express it

Question 23

Optimally modelling

Answer 23

The investigator uses a hypothesis derived from reverse engineering and guesses with the use mathematical forms under natural selection what design features would we expect to have?

Question 24

Nomological networks

Answer 24

A network based on different sciences to find a proof for evolution/selection
Should be combined and not subject focused

Question 25

Sexual dimorphism

Answer 25

The difference between male and female forms of the same species

Question 26

Sexual selection

Answer 26

is natural selection on the ability to gain mates

Question 27

Batemans principle

Answer 27

male reproductive success increases with each additional partner mated to a greater extent than is true for females

Question 28

Lek

Answer 28

The showoff from males to impress on females to be able to have sex with them

Question 29

Intrasexual competition

Answer 29

An example would be fighting of males

Question 30

the sexy son hypothesis

Answer 30

if there is any initial slight preference amongst females for a males with longer trails, then the preference for the long tail and the length of tze tail itself co-evolve to both become even greater over time.

Question 31

The good genes hypothesis

Answer 31

Special looks are costly so they are supposed to have enough spare energy to evolve them.

Question 32

Extra-pair matings

Answer 32

matings that take place with a male other than the social partner
o Females using extra-pair matings to get better genes for their offspring

Question 33

Sex ratio

Answer 33

The sex ratio is always 50/50 and selection would bring it back if it changes
• Birds with nest helpers in high quality territories were higher in reproductive success, but when the territories were low in quality any helper decreased the reproductive success (this accounts for no 50/50 distribution)
• Local resource competition, and local resource enhancement, are two examples in which deviations from a 50:50 sex ratio have been successfully predicted

Question 34

Founder effect

Answer 34

few individuals become isolated from larger population and establish a new gene pool different from source population

Question 35

Bottleneck effect

Answer 35

few individuals become isolated from larger population and establish a new gene pool different from source population

Question 36

Neutral variation

Answer 36

differences in DNA sequence that don’t give an organism a selective advantage/ disadvantage

Question 37

Mutation selection balance

Answer 37

mutation introduces genetic variation into population while selection reduces it
–>level of genetic diversity depends on the relative strength of the two