Natural selection (Lucy)

Question 1

What were the 3 inferences Darwin made about natural selection?

Answer 1

1 - Fierce struggle for existence

2 - Hereditary constitution of the surviving individual

3 - Continue gradual change of population

Question 2

Who was Alfred Russel Wallace?

Answer 2

British naturalist, biologist etc

Best known for independently concieving the theory of evolution thru natural selection - his paper on the subject was jointly published w some of Charles Darwin’s writings

Prompted Darwin to publish origin of species

Question 3

What did Darwin hypothesise about natural selection?

Answer 3

(Common ancestory of all living things)

He hypotheseized that all species have descended from on of few common ancestors

New species do not arise from independent acts of creation or spontaneous generation but from pre-existing species

Branching pattern of ancestry that connects all life

Question 4

How did Darwin’s ideas compare to Lamarck’s?

Answer 4

Lamarck suggested independent progression whereas Darwin proposed the branching tree of life

Question 5

What are the 3 components of natural selection?

Answer 5

• Variation
• Inheritance
• Differential reproductive success

Question 6

What is variation?

Answer 6

Individuals in a pop differ from one another

Question 7

What is inheritance?

Answer 7

Some of these differences are inherited from their parents

Question 8

What is differential reproductive success?

Answer 8

Individuals w certain traits are more successful than others at surviving & reproducing in their environment

Question 9

Give an example of variation, inheritance & differential reproductive success causing natural selection:

Answer 9

Ladybirds:

• Variation = members of the pop vary in the traits they display, some are RED while others appear ORANGE
• Inheritance = offspring tend to resemble their parents
• Differential reproductive success = BRIGHTER bettles are BITTER –> predators learn to avoid them - SO - bright beetles more liekly to survive so more likely to reproduce
• Result = evolution by natural selection –> proportions of different variants in beetle pop will change over time

Question 10

How do mutations affect natural selection?

Answer 10

Mutations = major source of variation on which natural selection acts

Mutations are random - no respect to needs of organism, independent of selection, most are random & harmless

Question 11

Does natural selection act on genotypes or phenotypes?

Answer 11

Phenotypes –> this is bc gene codes for a trait but it only appears under set conditions

Question 12

Give an example of phenotype depending on both genotype & environment:

Answer 12

Yarrow plants (Achillea millefolium)

Depends on its genotype & the altitude at which it is raised

(Rest of description):
Pops of yarrow plants grown in gardens at three sites that were at different altitudes: high, medium, and low elevation. For example, the green screen behind the plants of genotype 1 shows that these plants grow tall at high and low elevations, but are short at medium elevation. The blue screen behind the plants of genotype 4 shows that these plants respond very differently to elevation. This genotype grows tallest at medium elevation and shorter at high and low elevations. Adapted from Clausen, Keck, and Hiesey (1940, 1948).

Question 13

What are levels of selection?

Answer 13

Consistent differences in fitness among phenotypically (and genetically) different individuals w/in pops

Selcetion acts on genes, cell types, individuals, (pops & species)

Question 14

Give examples of levels of selection:

Answer 14

e.g. selfish genes, transponsons

e.g. segregation, distortion, meiotic drive - do not follow Mendel’s laws; mouse t allele kills sperms that carry normal T allele, so 90% of sperm carry t –> tt. individuals die/are sterile

Question 15

What is fitness? (Components of natural selection)

Answer 15

The ability of an individual (genotype) to survive (viability) & to reproduce (fertility)

Question 16

What is viability?

Answer 16

Probality of survival to reproductive age

Question 17

What is fertility?

Answer 17

Avg number of offspring per individual that survive to reproductive maturity

Question 18

What are the 2 divisions of fitness that we look at?

Answer 18

• Absolute fitness
• Relative fitness

Question 19

What is absolute fitness?

Answer 19

Represents the avg number of offspring (reproductive success) produced by individuals of a particular genotype

Question 20

What is relative fitness?

Answer 20

(More important in an evolutionary context)

Represents the avg no. offspring (reproductive success) produced by individuals of a particualr genotype relative to other members of the pop

Question 21

What was the first way which natural selection was measured in a wild population?

Answer 21

Beak size in Geospiza fortis

Birds arrived on Galapagos ~ 3 million yrs ago then rapidly diversified into different forms

Question 22

Why was measuring finches on the Galapagos islands an ideal study?

Answer 22

On Daphe major –> relatively untouched island, no goats, no farming & can measure every type of seed finches each

Question 23

How was natural selection mearured in finches (Geospiza fortis)?

Answer 23

1 - Beak size is heritable & size of beak makes a difference between life & death

2 - Drought in 1977 - spurge plants all died, so no small seeds availble

3 - In subsequent years, beak size was 8-11mm (9.2avg), afterwards it was 9.7mm = 15% bigger

4 - 5 yrs later - much rains, spurge seeded again, beak size dec again

Question 24

What was the lesson from the study on finches (Geospiza fortis) on the galapogus islnmads

Answer 24

NS is variable (e.g. had they arrived at diff time, would have seen diff effects)

• NS can occur at surprising speed
• The nature of NS can change over time

Question 25

Gave an example od phenotypes affecting natural selection:

Answer 25

Oldfield - beach mouse coat colour

Peromyscus polionotus lives in 2 different habitat inland on the dark soil of the oldfield (majority of its habitat) & on the beach (sandy), they show 2 colour patterns nicely matching their environments. The remarkable thing is that the Florida beaches and Islands where these mice are living are only 4000 to 6000 years old.

Hopi discovered considerable phenotypic variation in coat colour, both within and between populations. Also discovered considerable genetic variation at the Mc1R locus associated with coat colour

Question 26

What development was made from the coat colour study on mice?

Answer 26

Links phenotyes to genotypes –> Natural selection not only require variation but it requires inheritance. TWO PIGMENTS RESPONSIBLE OF COAT COLOR

Thru discvoery of Mc1R gene (Melacortin-1receptor)

Question 27

What does the Mc1R gene do?

Answer 27

Known to influence coat color in many species of mammals and birds, depending of its interaction with other genes this gene switches back and forth between producing a dark pigment eumelanin or a light pigment phaeomelanin

What is triggering the switch is a protein alpha-MSH (Alpha melanocyte stimulating hormone) when it triggers the production of eumelanin

But another protein can also bind to the MC1R receptor it is called ASP Agouti signal protein where the system switch to the production of phaeomelanin

SO we have a fantastic system and equilibrium between a receptor and two activators between two circulating molecules. It is a co-dominant system

SO ANY MUTATION CHANGES THE BINDING BETWEEN THE RECEPTOR AND THE ACTIVATOR WILL IMPACT THE EQUILIBRIUM leading to coat color polymorphism

Question 28

What is the most famous example of evolution by natural selection directly observed in the wild?

& give examples of this

Answer 28

Industrial melanism in the peppered moth

(A) The pale gray “typical” form and the melanic form on a tree trunk darkened by air pollution (left) and on a normal, nonblackened trunk (right).

(B) The decline in the frequency of the melanic form in three British localities, indicated by dots of different colors, as air pollution decreased during the late twentieth century. (B after [11].)

Question 29

Slide 28

Answer 29

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