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Evolution Flashcards

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Biology 101 flashcards
1
Q

Why is variation important in natural selection?

A

Variation refers to the phenotypic differences between individuals in the same species, is the raw material for natural selection, arises due to mutations, meiosis and sexual reproduction
- when env changes occur, the phenotypic variation amongst individuals results in the best adapted individual surviving better and reproducing more successfully than others as they will have a selective advantage and will be selected for through natural selection, hence the population can continue to survive
- since favourable allele frequencies will increase abd unfavourable allele frequencies will decrease, macroevolution occurs
- if not for variation, all organisms will either be selected for and the pop will continue to survive or all organisms will be selected against and extinction can occur

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2
Q

Role of natural selection in evolution

A
  • there is variation within a population caused by random mutations which resulted in formation of new alleles as well as sexual reproduction
  • individuals with more favourable characteristics will have a selective advantage and be selected for to survive, reproduce and pass down its favourable alleles to the offspring better, hence resulting in a change in allele frequency over time
  • over hundreds of thousands of generations, reproductive isolation can occur and a new species is formed (macroevolution occurs)
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3
Q

Why the population is the smallest unit that can evolve

A
  • a population is a group of interbreeding individuals with the same species
  • evolution involves a change in allele frequency in a population over successive generations
  • since a change in allele frequency can only be. measured in a population over successive generations over time, and not an individual, the population is the smallest unit that can evolve
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4
Q

Define biological evolution and explain link between microevolution and macroevolution

A
  • biological evolution is defined as descent with modification from a. common ancestor
  • microevolution refers to a change in allele frequency in a population over successive generations, occurs over shorter periods of time, no new species is formed
  • macroevolution occurs due to a change in allele frequency in a population over successive generations, occurs over longer periods of time, new species is formed
  • microevolution may lead to macroevolution given enough time
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5
Q

biological concept of species

A
  • reproductively isolated from other species
  • can interbreed to produce fertile viable offspring
  • share a common gene pool and have the same chromosome number (similar morphological, physiological and behavioural features)
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6
Q

genetic concept of species

A
  • a group of genetically compatible interbreeding organisms in a natural population that is genetically isolated from other such groups
  • different genetic species do not interbreed in nature, they are genetically different and evolve independently of one another
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7
Q

ecological concept of species

A
  • share a same ecological niche
  • niche is where an organism lives and its interactions with its environment
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8
Q

morphological concept of species

A
  • share similar body shape, size and structural features.
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9
Q

phylogenetic concept

A

smallest group of organisms that share a most recent common ancestor and can be distinguished from other such groups

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10
Q

explain how new species are formed with respect to geographical isolation and behavioural or physiological isolation within the same geographical location

A
  • ancestral population is separated into subpopulations due to a geographical boundary (sea)
  • the barrier prevented interbreeding and resulted in a disruption of gene flow
  • hence each subpopulations faces different selection pressures as they occupy different niches
  • individuals with favourable characteristics will have a selective advantage and be selected for to survive, reproduce and pass down favourable alleles to its offspring better
  • each subpopulation undergoes evolutionary changes independently of each other
  • overtime, there will be a change in allele frequency as the pop is subjected to natural selection and genetic drift and accumulated different genetic mutations
  • over hundreds and thousands of generations, the subpopulation will become reproductively isolate and. cannot interbreed to form fertile viable offspeing
  • hence new species is formed. through allopatric speciation and macroevolution occurs
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11
Q

Advantages of molecular methods of classifying organisms

A
  1. nucleotide data is objective, as molecular character states are unambiguous
  2. nucleotide data is quantitative, can be easily converted to numerical analysis, amenable to statistical analysis
  3. nucleotide data can be used to distinguish species that are morphologically indistinguishable due. to convergent evolution or because they are closely related
  4. changes in nucleotide sequences accumulate overtime with clockwork regularly, thus we can estimate time of speciation
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12
Q

How genetic variation arises in natural populations

A
  1. Mutations
    - gene mutations: substitution, deletion or insertion of a nucleotide that changes the triplet code and hence amino acid
    - chromosomal mutations( involve changes in chromosomal number or structure)
    number: polyploidy/aneuploidy
    structure: deletion, duplication, inversion, translocation
  2. Meiosis
    - independent assortment and segregation of homologous chromosomes during metaphase and anaphase 1 respectively
    - independent arrangement and separation of sister chromatids during metaphase 2 and anaphase 2 respectively
    –>results in gametes with numerous combinations of maternal and paternal chromosomes
    - crossing over of non-sister chromatids of homologous chromosomes during prophase 1
  3. sexual reproduction
    - random fusion of gametes
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13
Q

How recessive alleles are preserved in a natural population

A
  1. diploidy/heterozygote protection
    - a gene can be dominant/ recessive, expression of the dominant allele masks the expression of recessive alleles, thus even if recessive alleles may be less. favourable in the current environment, they persist because they are propagated in heterozygous individuals where the disadvantageous
  2. heterozygote advanantage
    - a form of balancing selection which occurs when heterozygotes have greater fitness than both kinds of homozygotes
  3. frequency-dependent selection
    - a form of balancing selection within a population. which is able to maintain stable frequencies of two phenotypic forms so the alleles coding for them are preserved
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14
Q

Biological classification

A

biological classification is the organisation of species according to their shared characteristics in a hierarchical manner into increasingly inclusive groups based on anatomical and more recently molecular data

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15
Q

phylogeny

A

organisation of species to show their evolutionary relationships
- comparing homologous characters which are passed down from ancestor to descendants

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16
Q

comparison between classification and phylogeny

A
  • phylogeny takes into account evolutionary rs while classification is based on overall morphological similarities and does not consider evolutionary rs
  • phylogeny is a system which assigns each organism and position on a phylogenetic tree based on its evolutionary rs with other organisms on the tree, while classification is a naming system where each organism is given a binomial name, and grouped into a domain, kingdom, phylum, class, order, family, genus and species using a hierarchical classification system
  • phylogeny uses a phylogenetic tree where more closely related organisms are grouped closer together, while classification uses binomial nomenclature
  • phylogeny uses morphological, anatomical and molecular characteristics and fossil record, while classification uses morphological characteristics only
  • phylogeny allows inference of common ancestors, while classification does not
  • phylogeny can infer how closely related 2 species are by looking at how recently they diverged from their common ancestor while classification cannot
17
Q

How evidence based on homologues identified in biochemical data, and. fossil record together with biogeography supports Darwin’s theory of evolution.

A

homology: refers to similar anatomical and molecular characteristics found in different species due to common ancestry
- these characteristics present in an ancestral organism developed into different forms as the result of natural selection, as they faced different environmental conditions with different selection pressures
- homologies suggest common ancestry – descended from a common ancestor (basic form of the pentadactyl limb) –> homologies show descent with modification – show how an ancestral homologous trait may have been modified in descendent species through natural selection, homologies provide basis of comparison

18
Q

How anatomical homologies support Darwin’s theory of natural selection?

A
  • organisms with anatomical homology have morphological structures such as bones that they share with a common ancestor
  • e.g. pentadactyl limb: homologous structure in forelimbs of all tetrapods, same arrangement of bones but have different functions and look different, the limb structure in the common ancestor was altered by natural selection to suit their specialised functions, resulting in variations of the limb structure
19
Q

biogeography

A
  • study of the past and present geographical distribution of organisms
  • closely related species and their common ancestors should be in the same geographical region, differences amongst species was shaped by natural selection due to differences in local env
20
Q

fossils

A
  • show an ordered sequence of succession of organisms and how homologous structures have been modified through time
  • the study of fossils allows us to see the evolution through the modification of homologous structures from a common ancestor to the present descendant through a series of transitional forms
21
Q

How molecular homologies support Darwin’s theory of natural selection

A
  • organisms with molecular homology have similar DNA, RNA and amino acid sequences as they share a common ancestor that had these molecules
  • e.g. cytochrome C and p53 are homologous genes
  • homologous genes share significant sequence homology and when expressed produce proteins that have the same function in all organisms that possess them
  • nucleotide sequences in the ancestral genes were modified due to accumulation of mutations that occured over many generations and selection pressures favoured some individuals over others
  • the greater the sequence similarity between homologous genes, the more closely related the 2 species are

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