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Human Biology ATAR > Mechanisms/evidence for evolution > Flashcards

Mechanisms/evidence for evolution Flashcards

1
Q

What are 5 causes for variation?

A
  1. Random assortment
  2. Crossing over
  3. Non-dis-junction
  4. Random fertilization
  5. Mutations
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2
Q

What is random assortment?

A
  • Chromosomes are sorted into daughter cells randomly during meiosis, so there are many possible combinations of chromosomes that can come from the mother and father
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3
Q

What is crossing over?

A
  • Process where during meiosis, pieces of chromatids may be broken off and attached to a different chromatids
  • This results in a changed sequence, or recombination of the alleles along the resulting chromosome
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4
Q

What is non-dis-junction?

A
  • One or more members of a chromosome pair fail to separate during meiosis
  • This results in gametes that have more or less than the correct number of chromosomes
  • If such gametes are involved in fertilisation, the resulting embryo will have the incorrect number of chromosomes
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5
Q

What is random fertilization?

A

Chance alone is responsible for which sperm meets which egg

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6
Q

What are mutations?

A
  • Sudden and permanent changes in the DNA of a chromosome and may result in totally new characteristics in an individual
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7
Q

What is a species?

A

Organisms belonging to the same species who are capable of producing fertile offspring under natural conditions

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8
Q

What is a population?

A

A group of organisms of the same species living together in a particular place at a particular time

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9
Q

What is a gene pool?

A
  • The sum of all the alleles in a given population

- Can change over time

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10
Q

Allele frequencies

A
  • Can increase or decrease
  • Different populations have different allele frequencies
  • EG. Scandinavians have a high allele frequency for blue eyes and blond hair
  • EG. Chinese have a high allele frequency for straight dark hair
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11
Q

What is evolution?

A

A gradual change in phenotype thought to be caused by a change in allele frequency

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12
Q

What happens when there is a change in allele frequency?

A

Changes in allele frequency → phenotypic changes → the gene pool changes

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13
Q

Changes to allele frequency can be brought around by:

A
  1. Mutations
  2. Natural selection
  3. Random genetic drift
  4. Migration
  5. Barriers to gene flow
  6. Genetic diseases
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14
Q

What is a mutation?

A
  • A sudden and permanent change brought about by a change in the sequence of bases in a strand of DNA
  • Gene or chromosomal mutations
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15
Q

What are somatic mutations?

A
  • Body cells experience a mutation
  • Body cells arising from the mutant cell inherits the mutation
  • Subsequent offspring do not inherit the mutation
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16
Q

What are germinal mutations?

A
  • If a mutation occurs in a gamete, then any offspring resulting from this gamete will inherit the mutation
  • This mutation can then be inherited by following generations
  • This will change the allele frequency in the long term
  • Mutations may or may not affect the survival chances of an offspring
  • Mutations change allele frequencies
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17
Q

Natural selection

A
  • There is competition between individuals
  • Selection pressures make some genetic traits more favorable for survival
  • Those with the traits survive and reproduce
  • Favorable traits are passed onto offspring
  • The allele frequency of favorable traits increase
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18
Q

Random genetic drift

A
  • Only usually occurs in small populations
  • By chance (not because it is advantageous) the allele frequency in a population changes
  • Some random event (not associated with an increased chance of survival eg. An earthquake) change the allele frequency
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19
Q

An example of random genetic drift

A

EG. The Dunkers in Germany

  • Small religious group who only intermarry within the population
  • Their allele frequencies for blood groupings, mid-digital hair, ear lobes and handedness are markedly different from the general population
  • These features have no survival advantage
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20
Q

Islander group polulations

A
  • Have high IA allele frequency
  • No IB alleles
  • Mainlanders are the reverse
  • Blood groupings do not provide a survival advantage
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21
Q

The founder effect

A
  • A sub-group of random genetic drift
  • A small group moves away from the original population to begin a new population
  • The allele frequency of the emigrating group just happens to be different from the frequencies of the original population
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22
Q

Achromatopsia

A
  • Inherited total colour blindness
  • An example of random genetic drift
  • After a typhoon, only 20 people survived on a Micronesian Island
  • One of these was heterozygous for Achromatopsia
  • The current population now has a high frequency for this allele
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23
Q

Migration

A
  • A gene flow from one population to another
  • As individuals join a population, they change the allele frequencies
  • Large migrations have a considerable impact on allele frequencies
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24
Q

Barriers to gene flow

A
  • Can stop the interbreeding between populations
  • Isolated populations may be subject to different environments with different selection pressures
  • Results in different gene pools
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25
Q

Types of barriers to gene flow

A

Geographical barriers → ocean, river, canyon

Socio-cultural barriers → government, religion, race, income level

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26
Q

Genetic diseases

A
  • Can changes the allele frequencies in a population
  • It is expected that the frequency of a fatal allele will decrease in a population overtime
  • This is not always the case
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27
Q

Tay-sachs disease

A
  • A recessive autosomal trait
  • Homozygotes lack an enzyme that results in the accumulation of a fatty substance in the nervous system
  • Most frequently occurs in individuals of Jewish decent form Eastern Europe (1 in every 2500 births)
  • Frequency worldwide occurs 1 in every 500 000 births
  • Death usually occurs by the age of four or five
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28
Q

Reasons for this change in allele frequency (Tay-sachs)

A
  • Jewish populations have tended to be small and isolated, increasing the chances of genetic drift
  • Those who are heterozygous for Tay-sachs, have increased resistance to tuberculosis (TB)
  • If this is the case, heterozygotes have an advantage in situations where TB is prevalent
  • Individuals with two normal alleles would be more susceptible to TB, and would possibly die, while individuals with two Tay-sachs alleles would die in early life
  • Heterozygotes would have a survival advantage and would be more likely to reproduce and pass on their alleles to the next generation
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29
Q

Sickle-cell anaemia

A
  • Causes the flattening (sickling) of erythrocytes preventing them from carrying oxygen
  • Fatal in homozygotes
  • The allele frequency is unexpectedly high in some African populations
  • It was discovered that heterozygotes have a resistance to malaria
  • Homozygotes for sickle-cell anaemia would die from the disease
  • Homozygotes for healthy RBCs die from malaria
  • Heterozygotes have the greatest survival
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30
Q

Thalassemia

A
  • A recessive disease in which anaemia results from defects in the formation of haemoglobin
  • A reduction in the amount and shape of red blood cells
  • Homozygotes recessive have two defective genes, which can be fatal
  • Patients require regular blood transfusions and special drugs to remove excess iron
  • Homozygotes dominant do not have the disease
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31
Q

Heterozygote for thalassemia

A
  • High allele frequency along the Mediterranean coast
  • A carrier of the disease
  • They are normal except during surgery or pregnancy, where they may suffer from low haemoglobin
  • Have a slight change in the shape of their red blood cells and this allows them to be resistant to malaria
  • This is known as thalassemia minor
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32
Q

Evolution

A
  • A gradual change brought about by changes in gene frequencies
  • Thought to be responsible for the development of species (speciation)
  • Generally brought about by an increase in the frequency of advantageous alleles and a decrease in the frequency of disadvantageous alleles
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33
Q

3 observations made by Charles Darwin (in 1858)

A
  1. Variation exists and are passed from one generation to the next
  2. Birth rate exceeds resource availability
  3. Natures balance: although the birth rate of organisms was very high, each species number tended to remain at a relatively constant level
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34
Q

Conclusion from these observations (Charles Darwin)

A

Conclusion that because the excessive birth rate and limited resources, there must be a struggle for existence

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35
Q

Survival of the fittest

A
  • More organisms with favorable characteristics survived, while many of those with unfavorable characteristics died before they had an opportunity to reproduce and pass on the unfavorable characteristics
  • This is possible because variation exists within any species
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36
Q

The environment does not cause the mutation or change in the organism

A
  • An individual already has the mutation, but in its original environment, the mutation does not offer any advantage
  • The environment changes, and suddenly having the mutation is an advantage
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37
Q

4 steps to speciation

A
  1. Variation (exists)
  2. Isolation (occurs)
  3. Selection (applied/occurs)
  4. Speciation (resulting changes in gene frequencies make it impossible for the two groups to interbreed and produce fertile offspring)
38
Q

Types of evidence for evolution

A
  1. Fossils
  2. Comparative studies
    a. Comparative biochemistry
    - DNA
    - Mitochondrial DNA
    - Protein sequences
    - Genomics
    b. Comparative anatomy
    - Embryology
    - Homologous structures
    - Vestigial organs
  3. Geographical distribution
39
Q

Comparative DNA

A
  • All living organisms use the same bases in DNA
  • This supports the idea that organisms are related to each other
  • This supports the idea that all organisms have a common ancestor
  • When speciation occurs, the new species would have very similar DNA
  • There should be a gradual difference in the DNA as organisms become more distinctly related
  • Closely related organisms should have more similar DNA
40
Q

What is a Genome?

A

The complete set of DNA in an organism

41
Q

Junk DNA

A
  • Have no apparent function and appear to serve no purpose
  • Contain non-coding sequences of bases in the DNA
  • The more closely related the organisms, the more ‘Junk DNA’ they have in common
  • Supports the idea of a common ancestor
42
Q

Endogenous retroviruses (ERV)

A
  • A viral sequence that becomes part of an organism’s genome
  • Store their genetic information as RNA, not DNA
    upon entering a cell, a retrovirus copies it’s RNA genome into DNA (reverse transcription)
  • The DNA becomes inserted into one of the host cell’s chromosomes, which is then passed onto future generations (in a gamete)
  • ERV’s make up 8% of the human genome
  • More closely related organisms have more ERVs in common
  • Distantly related organisms have fewer ERVs in common
  • This supports the idea of a common ancestor
43
Q

Mitochondria

A
  • Organelles in the cell where the aerobic phase of respiration occurs to release energy for use by the cell
  • Contains small amounts of DNA called mitochondrial DNA
44
Q

Mitochondrial DNA

A
  • Does not form threads, instead forms circular molecules
  • 5-10 molecules in each mitochondrion
  • Inherited from the maternal parent (sperm mitochondria is destroyed in fertilisation)
  • Mutates at a faster rate than nuclear DNA and has gradually evolved
  • Can be used to determine the closeness of the relationship between organisms
  • Supports the idea of a common ancestor
45
Q

Number of genes in mitochondrial DNA

A
  • Has 37 genes, essential for the mitochondrion to function normally
  • 24 of the genes contain the code for making transfer RNA molecules involved in protein synthesis
  • 13 genes that code for enzymes necessary for reactions in cellular respiration
46
Q

Protein sequences

A
  • By comparing the type and sequence of amino acids in similar proteins form different species, the degree of similarity can be determined
  • Animals from the same species have identical amino acid sequences in their proteins
47
Q

Ubiquitous proteins

A
  • Found everywhere

- Carry out the same function in all organisms (from bacteria to humans

48
Q

Cytochrome C

A
  • An example of a ubiquitous protein
  • Performs an essential step in the production of cellular energy
  • Contains 104 amino acids
  • 37 of these amino acids have been found at the same position in every cytochrome C molecule that has ever been tested
  • This supports the idea of a common ancestor
49
Q

Annotation

A

The process by which genes and DNA sequences of a species are identified

50
Q

Comparative genomics

A
  • Differences and similarities between species are identified
  • A high level of similarity or a smaller amount of time since the two species diverged from a common ancestor shows a close relationship between organisms
  • Can be depicted by the construction of a phylogenetic tree or a cladogram
51
Q

What do poly-genetic trees represent?

A

The evolutionary relationship among groups of organisms that are believed to have a common ancestor

52
Q

What do the tips represent?

A

A species

53
Q

What do the nodes represent?

A

A common ancestor or when an organism has undergone speciation

54
Q

What do two descendants that split from the same node represent?

A
  • Each other’s closest relatives
  • Have a lot of evolutionary history
  • Have a common ancestor that is unique to them
55
Q

What is the single branch point from which all branches originate?

A
  • Called the root of the tree

- The nodes closest to the root of the tree represent a common ancestor for all organisms in the tree

56
Q

The longer the line….

A

The more time that has gone by

57
Q

Explain how closely related organisms are using DNA sequences

A
  • The less differences there are in DNA sequences, the closer the organisms are on the polygenetic tree
58
Q

What is embryology?

A
  • Comparing the very early stages of the development of organisms
  • Although it is easy to distinguish between adults of different species, it is difficult to tell the difference between the embryos of different species
  • All vertebrate embryos have gill arches and sacs, regardless of the type of respiratory organs found in the adult
  • These embryos also lack appendages and have substantial tails
  • This supports the idea of a common ancestor
59
Q

What are homologous structures?

A

Organs that are similar in structure but may be used for a different function

60
Q

Front limb

A

The high degree of similarity between these structures supports the idea of a common ancestor

61
Q

Vestigial organs

A
  • Structures that are reduced in size and now appear to have no function
  • The presence of organs not required (non-functioning) supports the idea of a common ancestor
62
Q

Examples of vestigial organs

A
  • Nictating membrane
  • Muscles to move ears
  • Pointed canines
  • Nipples on males
  • Wisdom teeth
  • Appendix
  • Coccyx
  • Erector pili muscles
  • Wings in emus
  • Pelvis and femurs in whales
63
Q

Geographical distribution

A
  • Isolated regions often evolve their own distinctive plant and animal populations e.g. Marsupials in Australia or different finches on different islands of the Galapagos
  • Over many generations, natural selection would have favoured those characteristics that aided in survival in a particular set of conditions
  • This also supports the theory of evolution
  • Over years (and generations) random traits that provide an advantage in that particular area (environment) become common due to natural selection
  • The allele frequency for particular traits become more common in particular areas
64
Q

What is a fossil?

A

Any preserved trace or evidence left by a previously living organism

e.g. bones, teeth, footprints, faeces, burrows or egg shells

65
Q

What is an artefact?

A
  • Any object made by a human
  • Can also be a fossil
  • E.g. cave paintings, ancient pottery or arrow heads and weapons
66
Q

What do fossils show?

A
  • The sequence of development in plant and animal species
  • The sequence of different life forms as they appeared on earth
  • The sequence of changes in speciation
67
Q

Fossil formation

A
  • Very few organisms form fossils
  • Most dead organisms undergo bacterial decay
  • Predators and scavengers also prevent fossil formation
68
Q

Things that enhance fossil formation

A
  • Drifting sand, mud and volcanic ash
  • Rapid burial
  • Alkaline soils produce the best fossils as the minerals in the bones are not dissolved
69
Q

What happens during fossilisation?

A
  • New minerals (from the soil) are deposited in the pres of the bone
  • The bone becomes petrified, but details of the structure are preserved
70
Q

What happens in wet, acidic soils?

A

No fossilisaiton occurs

71
Q

What happens in wet, acidic soils, with no oxygen (peat)

A

This may result in complete preservation of both the bones and the soft tissues

72
Q

What is dating fossils?

A

Determining the age of the fossils

73
Q

What is absolute dating?

A
  • Stating the actual age of the fossils

- E.g. He is 20 years’ old

74
Q

What is relative dating?

A
  • Giving comparisons between the age of fossils

- E.g. He is older than her

75
Q

Methods of absolute dating

A
  1. Potassium – argon dating
  2. Carbon 14 dating
  3. Tree ring dating
76
Q

Methods of relative dating

A
  1. Stratigraphy

2. Fluorine dating

77
Q

Carbon-14 dating

A
  • Based on the decay of the radioactive isotope, carbon 14
  • Produced in the upper atmosphere by the action of cosmic radiation on nitrogen at about the same rate at which it decays
  • When green plants undergo photosynthesis, carbon-14 is absorbed
  • Animals then eat the plants and the carbon-14 becomes a part of the animal’s tissue
  • At death, the amount of C14 begins to decline at a fixed, exponential rate
  • Therefore, the age of the sample can be determined by the amount of C14 present
78
Q

What does the rate at which carbon 14 forms =?

A

The rate at which it decays

79
Q

The amount of C14 in the atmosphere =

A

Constant

80
Q

The amount of C14 in living organisms =

A

Constant

81
Q

The half-life of C14 = 5700 years

A
  • In 5700 years, the amount of C14 is reduced by half (1/2)
  • In another 5700 years, the amount of C14 is reduced by half again (1/4)
  • In another 5700 years, the amount of C14 left is reduced by half again (1/8)
82
Q

Positives of carbon 14 dating

A
  • It is a form of absolute dating, and provides an exact age of the organism
83
Q

Negatives of carbon 14 dating

A
  • Normal radio carbon dating requires at least 3 grams of organic material
  • Can only be used on organic materials
  • Can only be tested on materials less than 70000 years’ old, otherwise there is not enough carbon 14 present test
84
Q

Accelerator mass spectrometry (AMS) radiocarbon dating

A

Requires only 100 micrograms of organic matter

85
Q

Potassium – argon dating

A
  • Based on the decay of radioactive potassium to form calcium and argon
  • Decay takes place at a slow but constant rate
  • Found in magma and lava, and decays as soon as it hits the atmosphere
  • Measures the amount of calcium and argon compared to potassium
  • Young (new) volcanic rock has lots of K and little Ca/Ar
  • Old rock has lots of Ca/Ar and little K
86
Q

Positives of potassium – argon dating

A
  • Absolute dating (exact age)

- Has a slow half life

87
Q

Negatives of potassium – argon dating

A
  • Can only be used on volcanic rocks
  • Only useful for old rocks (> 200,000 years old)
  • It assumes that the fossil inside is the same age as the rock
88
Q

Tree ring dating

A
  • Trees grow one concentric ring in the trunk per year
  • Good year → fatter ring
  • Bad year → thinner ring
  • Count rings → know the tree’s age
  • Use of live and dead bristle cone pines (USA) have provided marker rings up to about 8600 years’ old
  • Only useful if the tree is
89
Q

Stratigraphy

A
  • Rule of superposition says deeper layers are older

- Must take into account folding of layers, faulting and erosion

90
Q

Index fossils

A
  • Widely distributed for a short period of time

- Can compare the age of fossils to known index fossils

91
Q

Fossil formation requires (limitations):

A
  1. A quick burial of remains
  2. The presence of hard body parts
  3. An absence of decaying organisms
  4. A long period of stability

Human Biology ATAR (13 decks)

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