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Flashcards in Natural Selection Deck (57)
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1

General principle of Thomas Malthus

populations could grow exponentially but in practice they dont ; therefore they must be limited by incomplete survival or reproduction
-> competition bw members of same population to be in the part of population that survives and reproduces

2

Mutation and Environment

Mutation is unrelated to demands of environment

3

Fitness of an allele


-> fitness is defined as the number of offspring that organisms with a particular genotype or phenotype leave behind, on average, as compared to others in the population

4

absolute / direct fitness

contribution of an individual to the gene pool of the next generation ( How many childrens a person has)

5

relative / indirect fitness

the contribution an individual makes to the gene pool of next generation relative to contributions of other individuals ( eg more efficient food collection -> more power -> more eggs )

6

How does natural selection change allele frequency?

natural selection increases the frequency of those alleles with high fitness and eliminates alternative alleles with low fitness
-> causes evolution by selecting favorable phenotypes

7

adaptive evolution

evolution resulting in better match between organisms and their environment

8

Linnean hierarchy

history of life with organisms at avrious levels related through descent from common ancestors

9

genetic drift

random chance events cause allele frequencies to fluctuate unpredictably from one generation to the next
-> more likely to occur in small populations

-> GENES IN CURRENT ARE ONLY SAMPLE OF GENES CARRIED BY PREVIOUS GENERATION -> things get lost

10

consequences of genetic drift

can lead to loss of genetic variation -> influences how effectively population is

11

Founder effect

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

12

Bottleneck effect

sudden change in environment drastically reduces size of population ( major disaster) ->one small part of population survives
-> by chance certain alleles are over/under represented or absent

13

gene flow

- reduce genetic differences

traveling -> mating -> gene flow -> populations become more similar

14

Mutation-selection-balance

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

15

Important point on natural selection and allele frequency

1 not necessarily organism but alleles with highest fitness will preserve
2 selection acts more directly on phenotype than on genotype

16

Purifying selection

- the selective removal of alleles that are deleterious
- makes sure that deleterious mutations cannot take over a population and that any improved structures—once fixed in a population—are maintained as long as they are needed.
-> getting rid of the extremes

17

Phenotypic plasticity

ability of one genotype to alter phenotype when exposed to different environments ( without altering its genome)

18

Stabilizing Selection

intermediate phenotypes are more fit than extreme ones
-> individuals higher or lower the average having worse reproductive fitness
-> reduces variation and maintains status quo

19

Directional Selection

one extreme phenotype is more fit than all the other phenotypes -> shifts overall makeup -> adaptation

20

Disruptive Selection

occurs when condition favours variants at both extremes of a phenotyic range over intermediate phenotypes

21

Heterozygote advantage

situation where individuals with one copy of a particular allele have higher fitness than individuals with either no or two copies
example sickle cell trait, which protects against malaria in heterozygotes, but causes a deadly disease in homozygotes

22

negative-frequency-dependent selection

where a phenotype is associated with relative high fitness when it is rare but low fitness when it is common

23

positive-frequency-dependent association

altruism, the more people it have, the better

24

force of mutation

genetic mutation will persist when force of mutation is strengthened or that of selection weakened

25

inconsistent ( unbeständig) selection

reason why variation may persist is if selection is inconsistent
-> decreases particular allele in one year and increases it in another

26

sexually antagonistic selection

optimal phenotype may not be same in male and female

27

adaptationist stance / hypothesis

if some feature or behavior is commonly found in a type of organism then it is probably an efficient design solution to some problem the organism has faced

-> multiple perspective model shows some evidences that can be met

28

ultimate explanation

How a particular design increased ancestral fitness
-> more phenotype

29

proximate explanation

explanation of the genetic mechanism that led to the formation of a new characteristic
-> more genotype

-> natural selection favours whatever proximate mechanisms produces the optimal phenotype

30

example ultimate and proximate explanation :
Black tailed Prarie Dogs Alarm Calling

ultimate : call when kin is in danger - increases fitness
proximate: all kinds of proximate machanisms could produce the required effect