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Human Biology Y12 > mutations and gene pools > Flashcards

mutations and gene pools Flashcards

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1
Q

evolution

A

change in characteristics of a species over time. it is gradual change that occurs over a number of generations, rather than the change of a particular individual or generation.

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2
Q

Phenotypes

A

set of characteristics of individuals are a result of the alleles

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3
Q

genotypes

A

the combination of alleles for a gene

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4
Q

mutation

A

A sudden and random change in a gene or chromosome leading to new characteristics in an organism. Occurs purely by chance.

  • source of all new alleles
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5
Q

mutant

A

an organism that possesses a characteristic resulting from a mutation.

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6
Q

causes of mutation

A
  • spontaneous
  • induced
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7
Q

spontaneous mutations

A
  • arise from errors in replication
  • different genes mutate at different rates
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8
Q

induced mutations

A

mutations can be induced by mutagens (environmental factors that cause a change in DNA)

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9
Q

mutagen

A

agents that are known to increase the rate at which mutations occur

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10
Q

mutagen examples

A

saif:
- sulfur dioxide
- some antibiotics
- ionising radiation e.g. UV rays, X-rays and fallout from nuclear explosions
- formaldehyde

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11
Q

location of mutations

A
  • somatic mutations
  • germline mutation
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12
Q

somatic mutations

A
  • Somatic (body) cells are affected.
  • Only the person with the mutation is affected - cannot be passed on.
  • Each time a mutant somatic cell replicates after the point of mutation it passes the mutation to the daughter cells.
  • When the individual dies, the mutation is lost.
  • Involved in many cancerous growths
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13
Q

germline mutation

A
  • Reproductive cells (gametes) are affected.
  • The person with the mutation is NOT affected – but it can be passed on.
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14
Q

what happens if conception occurs with a mutated gamete?

A

it usually naturally aborts. However, some conditions such as PKU (cannot break down proteins and usually results in brain development retardation) can arise from mutated gametes.

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15
Q

effects of mutations (not amino acid related)

A
  • harmful mutations
  • neutral mutations
  • beneficial mutations
  • lethal recessive
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16
Q

harmful mutations

A

these mutations are harmful because they alter the DNA sequence, thereby upsetting the structure and function of the protein they code for

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17
Q

neutral mutations

A

these often produce little or no change in the phenotype, neutral mutations are hard to defect

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18
Q

beneficial mutations

A

these mutations are best observed in species with short generation times

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19
Q

lethal recessive mutation

A

Lethal recessives occur when a recessive trait can cause death if there is two recessive alleles inherited (in other words, not masked by a dominant allele).

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20
Q

Most gene mutations produce…

A

recessive alleles (to do with protein production)

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21
Q

two types of mutations

A
  • gene mutation
  • chromosomal mutation
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22
Q

gene mutation

A

changes in a single gene so that the traits usually produced by that gene are changed or destroyed. Occur during the replication of DNA before cell division. Even subtle changes to DNA can have significant effects. If a mistake occurs at this stage, each time the cell replicates, it will replicate the mistake too.

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23
Q

point mutation

A

a type of gene mutation which affects only one base (on DNA)

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24
Q

chromosomal mutation

A

all or part of a chromosome is affected. Types of chromosomal mutations next slide.

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25
Q

aneuploidy

A

loss or gain of whole chromosomes

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26
Q

polyploidy

A

loss of gain of complete set of chromosomes

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27
Q

point mutations

A
  • Point mutations change the sequence of bases in DNA for a single gene and may produce a new allele of a gene.
  • Single gene mutations involving a single nucleotide are usually called point mutations.
  • The new DNA sequence will result in a new sequence of amino acids making up a protein.
  • Because of the degeneracy in the genetic code not all changes in a DNA sequence will result in a new sequence of amino acids.
  • Even with a change in amino acid sequence, protein function may not be affected.
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28
Q

change in DNA

A

Change in the DNA

Mutations vary in the change in the DNA. Point mutations are due to changes in a single nucleotide; therefore, only one base is changed. These mutations may be due to a nucleotide being:

  • insertion
  • substitution
  • deletion
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29
Q

insertion

A

a new nucleotide is added to the DNA strand

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30
Q

substitution

A

an existing nucleotide is replaced with another one, with a different base

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31
Q

deletion (single gene)

A

a nucleotide is removed from the DNA strand

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32
Q

single gene mutation types

A
  • missense
  • nonsense
  • neutral
  • silence
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33
Q

missense mutation

A
  • a single base is substituted by another
  • causes a change in the amino acid, and therefore in the protein produced
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34
Q

nonsense mutation

A
  • a single base is substituted by another
  • this results in a new triplet that doesn’t code for an amino acid, changes base sequence to the code to STOP
  • means that the synthesis of the protein will stop, and so a shorter protein is produced that is unlikely to be able to fulfil its function
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35
Q

neutral mutations

A
  • cause a change in the amino acid; however, the amino acid is of the same type and doesn’t change the structure enough to change its function
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36
Q

silent mutation

A
  • do not cause any change in the amino acid, and therefore in the protein produced
  • this is possible as most amino acids are coded for by more than one base sequence
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37
Q

sickle cell mutation

A

point substitution mutation
- autosomal recessive mutation which results in the substitution of a single nucleotide

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38
Q

cystic fibrosis

A
  • single gene deletion mutation
    autosomal recessive, over 500 different recessive mutations
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39
Q

chromosomal/block mutation types

A
  • inversion
  • translocation
  • duplication
  • deletion
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40
Q

inversion

A

middle piece of chromosome falls out, rotates 180˚ and then rejoins, gene appears in reverse order

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41
Q

translocation

A

piece of one chromosome breaks off and joins onto another chromosome

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42
Q

duplication

A

Homologous chromosomes: a segment is lost from one chromosome and is added to its homologue
- pieces of chromosomes are repeated so there are duplicate segments

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43
Q

deletion

A

break occurs at two points on the chromosome and the middle piece falls out, two ends then rejoin to form a chromosome deficient in some genes

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44
Q

effects of chromosomal mutations

A
  • Could be larger effect than gene mutation as the mutation can effect all or part of a chromosome. Therefore, multiple genes.
  • Can cause mutations so severe that miscarriage occurs in the early stages of pregnancy
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45
Q

down’s syndrome

A

a relatively frequent chromosomal mutation resulting from non-disjunction. An extra chromosome 21 is inherited (Often referred to as trisomy – three chromosomes instead of two)

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46
Q

patau syndrome

A

extra chromosome 13. results in mental retardation and physical deformities such as extra fingers, cleft palate/lip, deformed eyes and ears…

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47
Q

monosomy

A

can also occur – missing a chromosome (one instead of two) such as Turner’s syndrome where an X chromosome is missing. Females with this condition would be infertile, short in stature and lack secondary sexual characteristics.

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48
Q

variation

A

diversity of genetic and phenotypic traits within and between populations

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49
Q

variation gives. species..

A

greater opportunity to adapt to and survive in dynamic environments

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50
Q

Populations of highly variable species include…

A

individual with different fitness in that environment
- This variability → offers chance of reproductive advantage if environments change

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51
Q

ultimate source of variation

A

Mutations are the ultimate source of variation introducing new alleles into a population; new alleles may be favourable or unfavourable to survival

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52
Q

Different genotypes produce…

A

a variety of phenotypes, which are acted on differently by factors in the environment, producing different rates of survival

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53
Q

Mutations in genes and chromosomes can result from…

A

errors in DNA replication, cell division or from damage caused by mutagens

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54
Q

Species with low variation (pop. of clones)

A

highly successful in stable conditions

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55
Q

species

A

group of individuals that share many characteristics; able to interbreed under natural conditions to produce fertile offspring

56
Q

alleles

A

alternative forms of a gene

57
Q

geneticists

A

study populations, they consider the characteristics of the population as a whole rather than individuals

58
Q

population

A

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

59
Q

gene pool

A

sum of all the alleles in a given population

60
Q

allele frequencies

A

how often each allele of a gene occursin a population

61
Q

Populations with different characteristics are likely to have…

A

different frequencies of the various alleles in their gene pools

62
Q

example of allele frequency

A
  • If the frequency of Cystic Fibrosis in a given population is 5% then this means 5 in every 100 members of that population carry the Cystic Fibrosis allele.
  • Cystic fibrosis is carried on chromosome 7. Therefore 95 out of 100 chromosome 7’s will have the regular allele and 5 out of 100 will have the cystic fibrosis allele.
63
Q

example of frequency of various alleles in gene pools

A

Scandinavians commonly have blue eyes, black Africans commonly have brown eyes. Therefore, the frequency for the blue eye allele would be much higher in the Scandinavian gene pool compared to the African gene pool.

64
Q

what also changes when allele frequencies for a population change?

A

gene pool would also change

65
Q

what chances can cause changes in allele frequency?

A
  • Pure chance: mutations
  • Natural means: changes to environment
66
Q

what processes cause changes in allele frequency?

A
  1. mutation
  2. gene flow (immigration and emigration)
  3. small population size and genetic drift
  4. natural selection
  5. non-random mating
67
Q

selection pressures

A

External agents which affect an organisms ability to survive in a given environment

68
Q

how can selection pressures be negative?

A

decrease occurrence of trait

69
Q

how can selection pressure be positive?

A

increase proportion of trait

70
Q

three examples of selection pressures

A
  • Resource availability
  • environmental conditions
  • biological factors
71
Q

selection pressure: resource availability

A

Presence of sufficient food, habitat (shelter/territory) and mates

72
Q

selection pressure: environmental conditions

A

Temperature, weather conditions or geographical access

73
Q

selection pressures: biological factors

A

Predators and pathogens (diseases)

74
Q

density dependent selection pressures definition

A

density-dependent - affected by population size

75
Q

density independent selection pressures definition

A

density-independent - unaffected by population

76
Q

selection pressures acronym

A

PANDA PAW

77
Q

density dependent selection pressures examples

A

PANDA
Predators
Availability of resources (e.g. shelter water)
Nutrient supply (i.e. food source)
Disease/pathogenic spread
Accumulation of wastes

78
Q

density independent selection pressures examples

A

PAW
Phenomena (e.g. natural disasters)
Abiotic factors (e.g. temperature, CO2 levels)
Weather conditions (e.g. floods, storms, etc.)

79
Q

variation

A

the natural differences that are present between individuals or species in a given species

80
Q

what are the causes of variation?

A
  • random assortment
  • crossing over
  • non-disjunction
  • random fertilisation
  • mutations
81
Q

random assortment

A

random assortment of chromosomes in meiosis resulting in many different combinations of chromosomes originally from each parent.

82
Q

crossing over

A

crossing over of chromatids in meiosis resulting in recombination’s of alleles.

83
Q

non-disjunction

A

results in incorrect numbers of chromosomes.

84
Q

random fertilisation

A

sperm and egg combinations are random

85
Q

mutations

A

mutations can result in new characteristics.
- Mutations result in brand new alleles to the gene pool therefore are considered the most important source of variation. If a mutation is beneficial to survival, it can result in change to the whole gene pool!

86
Q

changes to allele frequencies in gene pools

A
  • Natural selection
  • Random genetic drift (including Founder Effect)
  • Migration
  • Barriers to gene flow
  • Genetic diseases
87
Q

natural selection

A

the process by which a species becomes better adapted to its environment; those individuals with favourable characteristics have a survival advantage and so pass those characteristics on to subsequent generations

88
Q

what is a major cause of change to allele frequencies in a gene pool

A

natural selection

89
Q

evolution

A

a gradual change in the characteristics of a species

90
Q

who put forward the theory of evolution

A

Charles Darwin and Alfred Russel Wallace in 1858

91
Q

darwin’s three main observation

A
  • Variation: differences in members of the same species
  • Birth rate: living organisms reproduce at a faster rate than which their food supply would increase – therefore causing overcrowding.
  • Nature’s balance: although birth rate was high, each species tended to maintain its numbers at a relatively constant level
92
Q

struggle for existence

A

there is such due to high birth rate and limited resources

93
Q

Survival of the fittest

A

because there was a range of variations in a species, those with characteristics best suited to their environment were more likely to survive and those with the least favourable characteristics were likely to die before passing on those characteristics to offspring.

94
Q

Natural selection in humans

A

The environment of early humans had a big effect on the characteristics that were selected as the most suitable for survival in the region where they lived.

95
Q

natural selection example: body shape

A

Body shape/stature correlates with resistance to the cold weather. Shorter limbed statures have less surface area to body volume therefore less heat can escape via radiation. As a pose to areas with a hotter climate tending to a have higher frequency of tall, slender body shapes which has a higher surface area to body volume ratio.

96
Q

natural selection example: sickle cell

A

Sickle-cell trait in areas where malaria is prevalent. Malaria acted as a selective agent for the sickle-cell allele.

97
Q

principles of evolution through natural selection

A
  1. There is variation of characteristics within a species
  2. More offspring of a species are produced than can possibly survive to maturity
  3. Due to excessive birth rate, and limited resources, there is a struggle for existence-competition for survival
  4. The individuals with characteristics best suited to the environment have more chance of surviving and reproducing-survival of the fittest
  5. Favourable characteristics (those with survival value) are passed on to the next generation
  6. In the gene pool, the proportion of alleles that produce favourable characteristics gradually increases.
98
Q

sickle cell anaemia cause

A

caused by mutation of the gene that makes haemoglobin → distorts the shape of the red blood cell

99
Q

what causes incidence of sickle cell anaemia in diff parts of the world?

A

natural selection operating in human populations

100
Q

what causes incidence of malaria to increase

A
  • As humans began to clear forests of Africa for agriculture → changed environment → created additional breeding areas for mosquito
  • Increased food supply from agricultural production → human population to increase → more bodies for mosquitos to feed
101
Q

what genotype is required for sickle cell anaemia?

A

homozygous for a particular recessive allele

102
Q

heterozygous sickle cell anemia

A
  • show no ill effects unless oxygen in short supply
    • RBC show mild sickling
    • Carriers → have sickle-cell trait
103
Q

anaemia definition

A

Anaemia = condition in which where is a reduced amount of haemoglobin (Hb) in the blood; or reduced no. of RBC’s

104
Q

why is it called sickle cell anaemia?

A

Cells are inflexible → become stuck in the blood vessels → blockages → reduced amount of Hb

105
Q

complications of sickle cell anaemia

A

Fatigue, jaundice, organ damage, high blood pressure, heart failure

106
Q

effect on survival SCA

A
  • If person with SCA dies before reproducing → allele that causes disease is not passed onto the next generation
    • Expect that over many gens. the frequency of SCA allele would gradually decrease until eliminated from the population/removed from gene pool
107
Q

sickle cell allele occurs only in areas where…

A

malaria is prevalent

108
Q

discovery about SCA

A
  • Observations = malarial patients who were ‘sicklers’ had fewer malarial parasites than ‘non-sicklers’
  • Sickling allele had highest frequency in areas where the risk from malarial parasites was greatest
  • individuals with one sickle-cell allele were more resistant to malaria than those with normal Hb in their RBC
109
Q

heterozygotes SCA

A
  • Heterozygotes were less susceptible to infection from malaria than individual homozygous for normal Hb
  • Individuals heterozygous for SC allele have a survival advantage in areas where malaria is prevalent
110
Q

heterozygote advantage

A

genotype has a higher chance of survival than homozygous genotype

111
Q

gene flow

A

the transfer of the alleles from one population to another through migration

112
Q

migration

A

the movement of people from one area to another with the intention of settling permanently
- gene flow from one population to another population

113
Q

how are gene pools affected by migration

A
  • If immigrants to a certain population bring alleles that are not already there in that population, the allele frequencies will therefore be altered.
  • Migration can also bring new disease to areas which previously did not have the disease and thus cause rapid decrease in populating numbers – affecting the gene pool.
114
Q

example of migration with disease

A

Many Australian Aborigines died from diseases such as chickenpox after European immigration and thus any alleles they possessed were also lost from the gene pool

115
Q

what happens when a population is divided by a form of barrier

A

the two environments will not be exactly the same

116
Q

types of barriers to gene flow

A
  • geographical
  • sociocultural
117
Q

geographical barrier

A

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

118
Q

sociocultural barrier

A

such as economic status, religion, educational background and social barriers are barriers to interbreeding

119
Q

Changes due to genetic disease

A
  • An allele that causes an inherited fatal disease to be expressed is expected to gradually be eliminated from the population (such as lethal recessives). Therefore in these cases, the allele frequency reduces.
  • If an individual or individuals with a genetic disease migrates to a population which previously did not have that inheritable disease, then the allele frequencies could increase.
  • If the disease provides an advantage to a particular population, it can increase in frequency
120
Q

examples of changes due to genetic disease

A
  • Sickle-cell anaemia (one allele only) provides resistance to malaria and is common in African countries where Malaria is high
  • Tay-Sachs disease (one allele only) provides resistance to Tuberculosis (TB – bacterial infection of lungs) which can be common in small populations where it can be passed on easily.
121
Q

Random genetic drift

A

In small populations there is often random, non-directional variation in allele frequencies that occurs purely by chance.

122
Q

The founder effect

A
  • A phenomenon similar to random genetic drift which occurs when a small group moves away from its homeland to a new area and establishes a community which eventually expands.
  • Being a small sample of the original population, the alleles they possess wouldn’t be representative of the whole population but only a selection of it – reducing the gene pool and changing the common characteristics.
123
Q

genetic drift

A

Genetic drift is the random fluctuation of allele frequencies in a population from one generation to the next.

124
Q

consequence of a genetic bottleneck

A

Genetic drift is often a consequence of a genetic bottleneck i.e. it results from inbreeding brought about by the limited mating possibilities in a small community.

125
Q

effects of genetic drift

A

The effects of genetic drift can be amplified by differences in the number of children raised by couples, or individuals dying prematurely.

Genetic drift can result in:

  • traits being lost from small populations.
  • unusual traits, not commonly found in the parent population, and that are often non-adaptive, becoming established.
126
Q

population bottlenecks

A

Anything that creates a sudden drop in population size (e.g. wars, natural disasters or migration), or prevents individuals from breeding, reduces mating possibilities and can cause a genetic bottleneck.

127
Q

Founder effect

A
  • Founder effect is an example of a genetic bottleneck.
  • Founder effect occurs when a small number of people migrate and settle in a new area.
  • The founding population carry only a small fraction of the original population’s genetic variation. As a result, they may differ both genetically and in appearance, compared with the parent population.
128
Q

tay sachs as a example of founder effect

A
  • Ashkenazi Jews an example (high incidence of Tay Scahs)
    • Small original population
    • Some individuals carrying the allele for Tay-Sachs disease
    • Restricted breeding with gene pool/cultural isolation
    • Frequency of allele increases over time
129
Q

Species

A

group of individuals that share many characteristics; able to interbreed under natural conditions to produce fertile offspring

130
Q

All humans are the same species that means…

A

have the capacity to interbreed to produce fertile offspring

131
Q

Speciation

A

process of new species developing

132
Q

speciation over time

A

Over time → allele frequencies of each gene pool will change (depending on which characteristics are favoured for survival)

133
Q

speciation over generation

A

Over generations → populations will become less and less alike → develop characteristics that better suit them to respective environments

134
Q

what happens when two populations are isolated for long enough

A

environmental influences are different enough → major changes in allele frequencies within each pop could occur

135
Q

what happens when members of those populations may become so different

A

interbreeding no longer possible

136
Q

steps involved in speciation

A
  1. VARIATION = b/w individuals of a species
  2. ISOLATION = populations of same species are isolated without gene flow
  3. SELECTION = each population subjected to different selective agents, subspecies begin to form
  4. SPECIATION = allele frequency changes until they become so different that the two groups are no longer able to interbreed

Human Biology Y12 (12 decks)

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