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Biology SL > 5.2 Natural Selection > Flashcards

5.2 Natural Selection Flashcards

1
Q

what is the theory of natural selection and who is it by?

A
  • charles darwin
  • it is not necessarily the strongest or most intelligent that survives but ones most responsive to change
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2
Q

what is the process of natural selection? (5)

A
  1. inherited variation- there is genetic variation within a population which can be inherited
  2. competition - there is a struggle for survival (species tend to produce more offspring than the environment can support)
  3. selection - environmental pressures lead to differential reproduction within a population
  4. adaptations - individuals with beneficial traits will be more likely to survive and pass there traits on to their offspring
  5. evolution - over time, there is a change in allele frequency within the population gene pool
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3
Q

what are the key components of natural selection? (6)

A

Inherited variation - exists within the population
competition - results from an overproduction of offspring
environmental pressures - lead to different reproduction
adaptations - which benefit survival are selected for
genotype frequency - changes across generation
evolution - occurs within the population

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4
Q

what are the 2 types of variation?

A

discontinuous - distinct classes
continuous - range across a characteristic spectrum

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5
Q

what are 3 main mechanisms by which genetic variation between individuals? (3)

A
  • mutation - changing the genetic composition of gametes (germline mutation) leads to change characteristics in offspring
  • meiosis - via crossing over (P1) or independent assortment (M1)
  • sexual reproduction - the combination of genetic material from 2 distinct sources creates new gene combinations in offspring
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6
Q

what is a gene mutation? (2)

A

a change in the nucleotide sequence of a section of DNA coding for a specific trait
- new alleles are formed by mutation

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7
Q

what three things can gene mutations be?

A
  • beneficial - change the gene sequence (missense mutation) to create new variations of a trait
  • detrimental - truncate the gene sequence (nonsense mutations) to abrogate the normal function of a trait
  • neutral - mutations have no effect on the functioning of the specific features (silent mutations)
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8
Q

how does meiosis promote variation?

A

by creating new gene combinations via crossing over or independent assortment

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9
Q

how does crossing over promote variation through meiosis? (2)

A
  • involves the crossing over of segments of DNA between homologous chromosomes during (P1)
  • the exchange of genetic material occurs between non-sister chromatids at chismata
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10
Q

what is the consequence of crossing over? (3)

A
  • all four chromatids that comprise the bivalent will be genetically different
  • chromatids that consist of a combination of DNA derived from both homologous chromosomes are called recombinants
  • offspring with recombinant chromosomes will have unique gene combinations that are not present in either parent
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11
Q

what is independent assortment? (3)

A
  • when homologous chromosomes line up in M1, their orientation towards the opposing poles is random
  • the orientation of each bivalent occurs independently
  • so different combinations of maternal/paternal chromosomes can be inherited when bivalents separate in A1
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12
Q

how can you work out the total number of combinations that can occur in gametes?

A

2^n (n = haploid number of chromosomes)

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13
Q

how do you work out the total number of combinations if crossing occurs?

A
  • the number of different gamete combinations becomes immeasurable
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14
Q

what is sexual reproduction?(2)

A
  • the fusion of 2 haploid gametes resulting in the formation of a diploid gamete
  • the zygote then divides by mitosis and differentiate to form a developing embryo
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15
Q

why will random fertilisation by egg and sperm always generate different zygotes? (2)

A
  • due to meiosis resulting in genetically distinct gametes
  • Individuals will show variation despite shared parentage
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16
Q

why will populations lead to competition for survival?

A

a stable population will inevitably outgrow its resource base

17
Q

what is the process of competition for survival? (3)

A
  • when there is an abundance of resources a population will grow according to its biotic potential (exponential J-curve)
  • with more offspring there are less resources available to members of the population (environmental resistance)
  • this will lead to a struggle for survival and an increase in the mortality rate ( causing population growth to slow and plateau)
18
Q

why is competition for survival essential to Darwin’s -survival of the fittest?

A
  • any trait that is beneficial for competition survival will be more likely to be passed on to offspring according to natural selection
19
Q

what is the definition of adaptations?

A
  • features of organisms that aid their survival by allowing them to be better suited to their environment
20
Q

what different ways may adaptations be classified? (5)

A
  • Structural - physical differences in biological structures
  • Behavioural - differences in patterns of activity
  • Physiological - variation in detection and response by vital organs
  • Biochemical - differences in molecular compositions of cells and enzyme functions
  • Developmental - variable changes that occur across the life span of an organism
21
Q

why may biological adaptations be passed onto offspring when parent reproduce?

A
  • they have a genetic basis
  • organisms with beneficial adaptations will be more likely to survive long enough to reproduce and pass of these genes
  • organisms without these beneficial adaptations will be less likely to survive long enough to reproduce and pass on their genes
22
Q

what do adaptations result in?

A

differential reproduction within a species (allowing for natural selection to occur)

23
Q

what do alleles encode for?

A

phenotypic polymorphisms of a particular trait that may be beneficial, detrimental or neutral

24
Q

what do beneficial, detrimental or neutral traits mean?

A
  • beneficial alleles will better equip the organisms to survive and hence produce more offspring
  • detrimental alleles will harm the survival prospects of an organisms leading to fewer viable offspring
  • neutral alleles will not affect the organism survival prospects
25
Q

how does natural selection change the proportion of different alleles? (2)

A
  • as beneficial alleles improve reproductive prospects they are more likely to be passed on to future generations
  • detrimental alleles result in fewer offspring and are less likely to be present in future generations
26
Q

what constitutes beneficial or detrimental traits and why are allele frequencies constantly evolving in a population? (1)

A

environmental conditions

27
Q

what does adaptive radiation describe?

A

the rapid evolutionary diversification of a single ancestral line

28
Q

how does adaptive radiation occur? (2)

A
  • when members of a single species occupy a variety of distinct niches with different environmental conditions
  • members evolve different morphological features in response to the different selection pressures
29
Q

what is an example of adaptive radiation? (2)

A

variety of beak types in the finches of the Galapagos islands
- they have specialised beak shapes depending on their primary source of nutrition

30
Q

what are antibiotics?

A

chemicals produced by microbes that kill (bactericidal) or inhibit the growth (bacteriostatic) of bacteria

31
Q

In a bacterial colony over many generation, a small proportion of bacteria may develop antibiotics via gene mutation, and what may occur as a result of this is antibiotics are used? (4)

A
  • when treated with antibiotics, the resistance bacteria will survive and reproduce by binary fission (asexual reproduction)
  • the antibiotic-resistant bacteria will flourish in the absence of competition from other strains of bacteria (killed by antibiotics)
  • antibiotic-resistant bacteria may also give resistance to susceptible strains by transferring plasmids via bacterial conjunction
  • the introduction of antibiotic (selection pressure) has caused the antibiotic resistance gene to become more frequent (evolution)
32
Q

How has the evolution of antibiotic-resistant golden staph (Staphylococcus aureus) illustrated antibiotic resistance? (6)

A
  • golden staph caused infections on skin as well as other infections
  • these infections were treated using antibiotic methicillin
  • bacterial strains developed were resistant to this antibiotic (MRSA)
  • these strains proliferated while susceptible strains died out
  • MRSA infections are now especially present in hospitals and nursing homes where methicillin was commonly used
  • medical practitioners now prescribe alternate antibiotic agents to treat infections caused by golden staph

Biology SL (38 decks)

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