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12 HUMAN BIO ATAR > CH 9 EVOLUTION > Flashcards

CH 9 EVOLUTION Flashcards

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Biology 101 flashcards
1
Q

define evolution

A

change in characteristics of a species over time

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2
Q

define population

A

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

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3
Q

what is a gene pool

A

the sum of all the alleles in a given population at a particular time. grouped by genotypes.

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4
Q

what is the allele frequency?

A

how often each allele of a gene occurs in the gene pool for that population.

e.g. if the frequency of the cystic fibrosis allele in a given population is 5%, then among population members, 5 in every one hundred of chromosome 7 will carry that allele.

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5
Q

what is a mutation?

A

a change in the gene or chromosome which causes new variation of the gene/trait.

  • they can be harmful to the individual, but not always.
  • mutant: an organism with a mutation
  • occurs during mitosis or meiosis
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6
Q

what are the two MAIN types of mutations? (categorised by the location of the mutation)

A

gene mutation: changes to a single nucleotide sequence / gene, the traits produced are normally destroyed
chromosomal mutations: all part of the chromosome is affected

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7
Q

what can cause a mutation?

A
  • there is no known cause
  • mutagens/mutagenic agents increase the rate of occurrence of mutations
    e. g. mustard gas, sulphur-dioxide, some antibiotics, all kinds of ionising radiation
  • large amounts of x-rays during first tri. of pregnancy may cause the child to be born with intellectual disabilities, skeletal malformations or microcephaly
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8
Q

how can the change in the base sequence affect the production of a protein?

A

change in base > change in AAs > change in protein produced

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9
Q

what are the types of mutations? (based by cause)

A

induced: due to mutagens
spontaneous: due to random biological error

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10
Q

what are the types of mutations? (based by heritability)

A

somatic: cell mutation passed on to daughter cells. reproductive cells not affected. stays with the individual. and can be the result of mutagens
germ-line: reproductive cells affected, mutation occurs in gametes, is passable to subsequent generations. parents aren’t usually affected
- if conception occurs involving one of the affected gametes, the embryo often dies naturally in early pregnancy, e.g. phenylketonuria (PKU)

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11
Q

what are the 4 types of mutations? (based on effect)

A

missense: cause a change in the amino acid, therefore the protein produced
nonsense: change in the base sequence to the code to STOP. synthesis of the protein will stop, and a shorter protein is produced that is unlikely to fulfil its function.
neutral: change in amino acid, AA of the same time does not change the structure of the protein enough to change its function
silent: no change in AA, therefore normal protein is produced. most amino acids are coded for by more than one base sequence.

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12
Q

define point mutations

A

change in just one base of a DNA molecule

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13
Q

why might a point mutation occur?

A

insertion: new nucleotide added to DNA strand
substitution: existing nucleotide is replaced with another one, with a different base
deletion: a nucleotide is removed from a DNA strand

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14
Q

what is a frameshift?

A

occurs when bases have been added or removed. when one base is added, it alters the sequence by moving each base along by one. this affects the production of many proteins.
there is no effect if 3 bases are added or removed

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15
Q

what can cause a mutation to affect a larger section of DNA?

A

duplication: section of a chromosome occurs twice
deletion: a piece of DNA is removed
inversion: breaks occur in a chromosome and the broken piece joins back in but the wrong way around
translocation: part of a chromosome breaks off and is rejoined to the wrong chromosome

non-disjunction: during meiosis, a chromosome pair does not separate and so one daughter cell has an extra chromosome and one has one less chromosome than the normal number. these are sometimes referred not as mutations but as ‘aneuploidy’ (a change in the chromosome number)

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16
Q

what is Duchenne muscular dystrophy and how does it occur?

A
  • disease results in wasting of the leg muscles and later the arms, shoulders and chest
  • usually apparent around the age of 3 or 5, when weakness becomes evident
  • death occurs eventually due to failure of respiratory muscles
  • may occur through gene mutation
  • may arise through mutation in the mother, which can be inherited by her sons
  • mutation may also occur in a male zygote so that the child develops the disease
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17
Q

what is cystic fibrosis and how does it occur?

A
  • genetically determined disease caused by a mutation
  • mutation occurs in a huge gene on chromosome number 7
  • the gene has the code for 1480 amino acids that make up a protein that regulates the passage of chloride ions across the cell membrane.
  • without the correct protein; the person suffers from salty tasting skin, persistent coughing, wheezing/pneumonia, digestive and other problems
  • recessive
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18
Q

what is trisomy?

A
  • result of non-disjunction
  • one chromosome too many or one too little
  • chromosomal mutation
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19
Q

what is down syndrome?

A
  • trisomy 21 - 3 chr 21s
  • characteristic facial expression, intellectual disability and weak muscles
  • may suffer from birth defects e.g. heart defects or digestive abnormalities
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20
Q

what is Patau syndrome?

A
  • extra chromosome 13
  • intellectual disability, microcephaly, extra finger on each hand, cleft palate and/or cleft lip, malformations in ears or eyes
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21
Q

how can trisomy occur with the sex chromosomes?

A
  • in males, non-disjunction may occur during either the first or the second meiotic division, producing individuals either XXY or XYY
  • XXY are normal as boys but later develop Klinefelter syndrome; small testes, do not produce sperm, enlarged breasts, body hair sparse. occasional intellectual disability.
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22
Q

what is monosomy?

A
  • missing a chromosome
  • if an autosome is completely missing, monosomy usually results in severe malformations and miscarriage
  • partial monosomy: only part of the chr is missing
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23
Q

what is Cri-du-chat syndrome?

A
  • missing portion of chromosome 5

- infant cry sounds like a meowing kitten due to problems with the larynx and the nervous system

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24
Q

what is Turner syndrome?

A
  • only one X chromosome

- short in stature, lack secondary sexual characteristics, are infertile

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25
Q

what are lethal recessives?

A
  • some recessive mutations can kill the individual if they are not masked by a dominant allele
  • can cause death of an embryo or foetus by miscarriage or spontaneous abortion or death in early childhood
  • these genes would decrease in frequency in a gene pool over time because the gene would die with the individual before they can reproduce and pass it down to future generations
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26
Q

what is Tay-Sachs disease (TSD)?

A
  • inherited disorder of lipid metabolism
  • autosomal recessive
  • caused by mutation in the HEXA gene that codes for beta-hexosaminidase (enzyme)
  • this enzyme breaks down toxic substances, including a fatty substance, GM2 ganglioside in the brain and spinal cord
  • the absence of the enzyme results in the accumulation of GM2 ganglioside which destroys the neurons
  • a baby with Tay-Sachs will develop normally for the first few months, and then deterioration that causes intellectual and physical disabilities begins
  • death usually occurs in early childhood
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27
Q

define gene flow

A

movement of genetic material from one population to another

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28
Q

what is migration?

A

when individuals move between populations and enable gene flow

29
Q

what is a ‘barrier’?

A

structures or concepts that inhibit the amount of interbreeding between populations. isolation leads to seperate gene pools forming

30
Q

give examples of geographical barriers

A

oceans, mountain ranges, large lake systems, deserts, expansive ice sheets

31
Q

give examples of sociocultural barriers

A

economic status, educational background, social position, religion, language

e. g. Australians tend to marry people with similar educational backgrounds
e. g. it is unlikely that people who cannot communicate with one another will marry

32
Q

what is special creation?

A

the belief that God or a supreme being had individually created each species

33
Q

what did Charles Darwin propose that animals were separated by?

A

geography - those living on the mainland of south America and those on the various islands
time - animals recently extinct and species still alive

34
Q

what did Carolus Linnaeus establish?

A

the basis of our present system of classification and the binomial system of naming organisms using generic (genus) and specific (species) names.

35
Q

what did Charles Lyell hypothesise?

A

the natural forces existing in the past were much the same as those living in his own time. implied that the earth’s surface has been gradually moulded over a long period of time, by such simple forces such as temperature, running water and earth movements.

theory of constant change

36
Q

what idea did Thomas Malthus provide?

A

foundation of Darwin’s theory of natural selection

- human population was increasing at a rate far exceeding the rate of food population

37
Q

what 3 observations was Darwin’s theory of natural selection based on?

A
  • variation: all members of a species vary, but characteristics are passed down from one generation to the next
  • birthrate: all living organisms reproduce at a rate far greater than that at which their food supply and other resources increase
  • nature’s balance: although the birthrate is very high, each species’ numbers tended to remain at a relatively constant level
38
Q

what did Darwin conclude from the three observations?

A
  • struggle for existence: excessive birth rate + limited resources
  • survival of the fittest: organisms with favourable characteristics survived, while many with unfavourable characteristics died before they had a chance to reproduce and pass on the trait
39
Q

what is variation?

A

the members of a species differ from one another in their physical characteristics, body functioning and behaviour

40
Q

what is a selective agent?

A

the environmental factor acting on the population

41
Q

do individual organisms adapt to an environment?

A

no, the species adapts to its environment by natural selection, and the process of adaptation takes many generations

42
Q

what are the principles of evolution through characterisation?

A
  • there is a variation of characteristics within species
  • more offspring of a species are produced than can possibly survive to maturity
  • because of excessive birth rate and limited resources, there is a struggle for existence or competition for survival
  • individuals with characteristics best suited to the environment have more chance of surviving and reproducing (survival of the fittest)
  • favourable characteristics are passed on to the next generation
  • in the gene pool, the proportion of alleles that produce favourable characteristics gradually increases

main 4 principles;

  • variation
  • heritability
  • the struggle for existence
  • survival traits
43
Q

how is body stature an example of natural selection?

A
  • those with shorter limbs lose less heat and therefore have a survival advantage in cold climates.
    e. g where Inuits live
  • those with longer limbs lose more heat and therefore have a survival advantage in warm climates
    e. g where Africans live
  • over time, the frequency of less favourable alleles would decrease and eventually, no longer occur within the population. the alleles more suited to the environment would increase.
44
Q

why did the incidence of malaria increase over time?

A
  • the Anopheles mosquito, which transmits the malarial parasite, is not normally an inhabitant of tropical forests
  • needs quiet, stagnant pools of water for breeding sites (often found in open areas)
  • humans began to clear forests for agriculture. this changed the env. in a way that increased breading sites
  • this also increased food supply for Anopheles mosquitos as agricultural production allowed human population to increase, providing more bodies for mosquitos to feed on.
  • thus, the incidence of malaria increased
45
Q

in sickle cell anaemia, what causes the RBCs to have their crescent-like shape?

A
  • sickle cell anaemia; homozygous recessive
  • occurs from a point mutation in the sequence of the HBB gene which codes for beta-globulin proteins that make up haemoglobin in RBCs
  • the altered base sequence causes the AA, valine, to be added instead of glutamic acid. a different form of the protein causes the haemoglobin to be altered, distorting its shape
46
Q

what happens to an individual if they are heterozygous for the sickle cell trait?

A
  • no ill effect unless in short o2 supply in which case their RBCs will show mild sickling
  • they are called carriers for sickle cell anaemia
47
Q

what can the sickle cell shape of the RBCs cause?

A
  • they often die early, causing anaemia
  • they are flexible and can get stuck in BVs, causing blockage
  • fatigue, jaundice, organ damage (kidneys, lungs, brain), high BP, heart failure
48
Q

since it would be common for a person with sickle cell anaemia to die before they can reproduce, what can we EXPECT will happen to the gene pool?

A
  • the frequency of the sickle-cell allele should decrease over time and diminish eventually
49
Q

what should happen if the ratio of mutation od normal alleles to sickle-cell alleles is great enough?

A
  • it could cancel out the loss of alleles through the death of affected individuals
  • this is NOT the case
  • investigations have shown that the rate of alleles being lost from the population is about 100 times greater than the average rate of mutation at any point along a human chromosome
  • some other mechanism must be at work to maintain the sickle-cell population
  • sickle cell allele only occurs in places where malaria is prevalent
50
Q

what did Anthony Allison discover?

A
  • 1954
  • 1st to notice relationship between malaria and sickle cell anaemia
  • sickle-cell allele tended to have the highest frequency in areas where the risk from malarial parasites was greatest
  • individuals with sickle-cell allele were more resistant to malaria than those with normal haemoglobin
  • malarial patients who were also ‘sicklers’ had fewer malarial parasites than ‘non-sicklers’
51
Q

what experiments did Allison conduct?

A
  • inoculated both sicklers and non-sicklers with malaria and then treated the individuals that the disease developed in
  • he concluded from the results that heterozygous were less susceptible to infection from malaria than individuals homozygous for normal haemoglobin
  • heterozygous individuals have a survival advantage in areas where malaria is prevalent
52
Q

how is the sickle-cell allele an example of natural selection?

A
  • heterozygote survival advantage
  • although recessive individuals died early with the allele before reproduction, heterozygotes had more of an advantage than normal homozygotes
  • the allele was passed on through the carriers
53
Q

what will happen to an individual who is homozygous recessive for Tay-Sachs?

A
  • have the disease
  • die at a young age before reproducing
  • do not pass on recessive allele
54
Q

what will happen to an individual who is heterozygous for Tay-Sachs?

A
  • reduced amount of beta-hexosaminidase
  • survive tuberculosis
  • reproduce and pass on alleles
55
Q

what will happen to an individual who is homozygous dominant for Tay-Sachs?

A
  • affected by tuberculosis

- may die prior to reproducing

56
Q

how does the heterozygous genotype of Tay-Sachs affect the gene pool in areas affected by tuberculosis?

A
  • in areas affected by tuberculosis, the percentage of the recessive allele increases due to the survival of carriers of the Tay-Sachs allele
57
Q

what is haemoglobin made up of?

A
  • four protein chains that fit together
  • 2 of which are alpha globin chains
  • the other 2 are beta globin chains
58
Q

what are the two types of thalassemia?

A
  • alpha: mutation in HBA gene on ch 16. reduced levels of alpha globin in haemoglobin
  • beta: mutation in HBB gene on ch 11. reduces levels of beta globin in haemoglobin
59
Q

what is thalassemia?

A
  • autosomal recessive
  • less haemoglobin in RBCs and therefore cannot carry as much oxygen in blood
  • severity varies depending on the number of affected genes, ranging from mild anaemia and fatigue to an enlarged liver and heart
60
Q

where are the types of thalassemia most prevalent?

A
  • both are common in areas of malaria
  • alpha is more prevalent in South-east Asia
  • beta is more prevalent in the Mediterranean basin
61
Q

how can Malaria act as a selective agent for thalassemia?

A
  • increase the frequency in alleles of alpha thalassemia
  • lower haemoglobin levels said to provide protection against malaria
  • thalassemia patients recover more quickly from malaria than those without thalassemia. may be due to increased blood cells
62
Q

what is genetic drift?

A
  • AKA random genetic drift or the Sewall Wright effect
  • random, non-directional change in allele frequency between generations
  • not affected by whether a gene is harmful or beneficial; purely by chance
  • unlikely to have significant effect on large populations, may play important role in evolution of small populations

e.g. if we put 50 black marbles and 50 red marbles into a bag and blindly elect 50 at random, we expect to pull out 25 of each colour, but it is not surprising or unusual if we select otherwise

the random selection can cause one colour to be selected more (e.g. 30 red, 70 black). if these marbles somehow reproduced, the incidence of a certain colour (black) will increase, due to no reason other than random chance

63
Q

give an example of how isolation can cause genetic drift

A
  • Aboriginal Australians; Bentinck and Mornington Islands in the Gulf of Carpentaria
  • both islands got randomly separated from the gulf by rising sea levels but Mornington were still able to communicate with mainland by using other islands as ‘stepping stones’
  • tested blood of Mornington, Bentinck and Bayley Point on the mainland
  • Bentinck had allele frequency values for blood groups that fall outside the range of Aboriginal people in the rest of aus
  • Bentinck show a very high frequency for B blood allele with the complete absence of the A blood allele
  • mainland had high frequency of A blood allele and low frequency of the B blood allele
64
Q

what are two mechanisms of evolution?

A
  • natural selection

- genetic drift

65
Q

what is the founder effect?

A
  • small group moves away from homeland to a totally new area and establishes a population which later expands
  • due to small size, chance can cause the new groups to have a different allele frequency from the original population and/or decreased genetic variation
  • this means that the new population may show a frequency of features that are not typical of the original homeland population
66
Q

what are the negative impacts of sickle cells?

A
  • less o2 transport

- higher chance of blockages

67
Q

what did Bentley Glass study?

A
  • isolated population in the US
  • the ‘Dunkers’ lives in Pennsylvania but came from Hesse, Germany. they are descended from old german baptist brethren who came to the US in the early 18th century
  • religion does not allow them to marry outside their group, thus they constitute an isolated breeding population within the total pop. of the US
  • study investigated easily measurable physical traits e.g. ABO, Rh, MN blood frequency, mid-digital hair, left/right-handedness, attached/free earlobes.
68
Q

what were the results of Glass’ study?

A
  • for most traits study, the Dunkers varied in allele frequency from the present day population of Hesse and also from the surrounding American pop.
  • the surrounding env. for the American population and the dunkers would be the same, so there would be no natural selection to account for the differences
  • Glass concluded that genetic drift was responsible for this variation as the small size of the Dunker population allowed certain characteristics to become common purely by chance

12 HUMAN BIO ATAR (13 decks)

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