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Ecology & Conservation Year 1 > APS125 Population Inheritance > Flashcards

APS125 Population Inheritance Flashcards

1
Q

What are Mutations?

A
  • Failure to replicate genetic information faithfully
  • Can affect the whole chromosome or singlegenes
  • Can be spontaneous or induced
  • The source of all genetic variation and is necessary fir natural selection and evolution
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2
Q

DEFINITION: Induced Mutation

A

When the presence of a mutagen increases the rate of mutation
Could be Radiation, UV, X Rays

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3
Q

DEFINTITION: Karyotypes

A

A method of displaying chromosomes from an organism and numbering them largest t smallest

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4
Q

DEFINITION: Polyploidy

A

When cells/ nuclei contain more than two sets of homologous chromosomes
In humans its always lethal, eg. after dispermy which results in 3 complete sets
Common in higher plants, bacteria are usually only monoploid with one circular chromosome

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5
Q

DEFINITION: Aneuploidy

A

When one set of chromosomes is incomplete, eg one is missing or and extra is present

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6
Q

3 types of Aneuploidy in Autosomes

A

Nullisomy (a pair of homologous chromosomes is missing)
Monosomy (only having a single pair of chromosomes rather than two)
Trisomy (one extra chromosome, usually lethal except during downs syndrome)

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7
Q

Aneuploidy in Sex Chromosomes

A

If lacking 45X it causes Turners Syndrome, lacking 45Y is inviable
Extra chromosome has minor effect due to X chromosome inactivation

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8
Q

DEFINITION: Translocations

A
  • Exchange of parts between non homologous chromosomes

- Carriers remain unaffected but offspring can have the wrong number of chromosome copies

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9
Q

DEFINITION: Deletions

A
  • Part of the chromosome is missing, patient will therefore only have one copy of the genes in that region
  • Severity depends on the size of the missing region
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10
Q

DEFINITION: Inversions

A

Paracentric- There are two break points in a chromosome and the in-between inverts
Pericentric- The same however the centromere is inside the two breaking points

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11
Q

Types of Coding Region Mutations

A
  • Substitutions

- Insertions/ Deletions

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12
Q

DEFINITION: Substitutions

A
  • Can be silent if base changes but does not change the overall amino acid
  • Or Replacement if the base changes the whole amino acid
  • Replacement of the middle base will never be silent
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13
Q

DEFINITION: Deletion/ Insertion

A
  • Deletion/ insertion causes a shift which changes the reading frame and produces a different protein
  • If entire codon is removed there is less change
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14
Q

DEFINITION: Phenotypic Polymorphisms

A

Mutation of one nucleotide eg. in Hb beta gene that leads to sickle cell anaemia or what decides the colour of a lizards neck

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15
Q

DEFINITION: Degenerate DNA

A
  • Means DNA can be coded by multiple different codons
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16
Q

DEFINITION: Gametic Mutation

A

Mutation in sperm/ egg cells

All heritable, can be severe, affects all cells

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17
Q

DEFINITION: Somatic Mutation

A

Occurs within body cells eg. cancers

Not heritable, usually but not always mild, doesn’t affect all cells

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18
Q

How to cross pollinate peas?

A
  1. Anthers removed before pollen is shed

2. Transfer the pollen to other plant by brushing the pollen onto the stigma

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19
Q

What is the ratio for mendelian inheritance?

A

3:1

Occurred with many different phenotypes in the F2 Progeny

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20
Q

Mendel’s suggestions about Experiment findings

A
  1. Alternative versions of a gene causes variation ( Alleles)
  2. An organism inherits two alleles, one from each parent
  3. Alleles can be dominant and recessive
  4. Alleles segregate during gamete production
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21
Q

Mendel’s First Law

A

Two members of a gene pair segregate from each other during gamete formation, half of the gametes carry one member of the pair and the other from another member

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22
Q

DEFINITION: Particulate Mechanism

A

Concept that parents pass on discrete heritable units (genes)
Derived from Mendel’s data

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23
Q

How was the first law verified?

A
  • Did a test cross of a heterozygote and homozygote recessive
  • Expected equal numbers of purple and white flowers after performing statistical tests
  • The data was significant so null hypothesis accepted and the numbers were equal
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24
Q

Dihybrid Crosses

A

Allow the tracking of two traits simultaneously

Ratio: 9:3:3:1

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25
Q

Mendel’s Second Law

A

Alleles of different genes segregate independently of each other, ( exceptions when genes are close together)
Known as Independent Assortment

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26
Q

How to verify Mendel’s Second Law

A

When crossing a homozygote recessive with a Heterozygote observed ration should be 1:1:1:1 which demonstrates independent assortment

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27
Q

DEFINITION: Blending Inheritance

A

Believed before Mendelian inheritance, however incorrect and would lead to a genetically uniform population

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28
Q

DEFINITION: Mendelian/ Monogenetic Diseases

A

Human diseases caused by one gene

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29
Q

DEFINITION: Multifactorial Diseases

A

Diseases caused by a combination of multiply genes

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30
Q

Uses for pedigrees

A
  1. Infer modes of inheritance

2. Genetic Counselling, eg risk of offspring inheriting a condition

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31
Q

Pedigree Symbol Definitions

A 
Squares-Male
Circles- Female 
White- Unaffected 
Black- Affected 
Diamond- Unknown Sex 
Black Dot- Carrier
Dash- Dead
Single Connecting Line- Marriage 
Double Connecting Line- Inbred Marriage
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32
Q

Autosomal Dominant Disease

A
  • Affected person usually has an affected parent
  • Affects both sexes
    -Transmitted by either sex
  • Roughly 50% chance of inheriting
    Examples: Widow peak, Polydactyl, Achondroplasia
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33
Q

Autosomal Recessive Disease

A
  • Parents usually carriers/ unaffected
  • Effects either sex
  • Increased by inbreeding
  • Carriers and non carriers are indistinguishable
    -If carriers mate there’s 1/4 chance of being affected and 1/2 of being a carrier
    Examples: Albinism, Sickle cell anaemia, CF
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34
Q

Cystic Fibrosis

A
  • Most common autosomal recessive disease in Europe
  • Affects lungs by increasing mucus production
  • Heterozygotes believed to have a selective advantage through resistance to typhoid, cholera
  • Caused by inactive copies of the CF transmembrane conductance regulator which is a CL- Channel
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35
Q

X Linked Recessive Disorder

A
  • Mostly affects males
  • 0.5 chance of male being affected if mum is carrier
  • Females only affected if mum is carrier and dad affected
  • Parents unlikely to show symptoms but mothers male relatives might
  • Mostly affects males as they’re XY so will always express it
  • Impossible for males to pass on to their sons
  • E.g Haemophilia
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36
Q

X Linked Dominant Disorder

A
  • Affects either sex
  • Offspring of affected female has 50% chance of being affected
  • All female children of affected males are affected
  • No make children of affected males are affected
    Example: Hypophosphatemia
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37
Q

X Chromosome inactivation

A
  • Lyonization
  • The inequality of X chromosomes in mammalian male and females is compensated for by X-inactivation
  • In each female cell one X is randomly inactivated
  • Occurs in early development and all daughter cells will have the same inactivated X
    Example: tortoise shell cats
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38
Q

X Linked Disorder

A
  • Only affects Males
  • Passed on to all sons but never daughters
  • Potentially hairy ear rims
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39
Q

T.H Morgan Fruit Fly Cross A

A
  • F1 Generation all red eyed Females and white eyes males (white is recessive)
  • F2 1/4 white eyed males as only have one X which always come from the mother
  • Females will always have red eyes
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40
Q

T.H Morgan Fruit Fly Cross B

A
  • F1 white eyed females, red eyed males

- F2 1/4 white males, 1/4 red male, 1/4 white female, 1/4 red female

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41
Q

Why does it matter that genes are on chromosomes?

A
  • There are lots more genes than chromosomes
  • Therefore sometimes genes will segregate together on chromosomes, and other times independently
  • Its important to see how far apart they are if on the same chromosome
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42
Q

Why might there be some variation in linked chromosomes?

A
  • Recombination occurs where chromatids cross over

- This however is rare and parental types are more common

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43
Q

How to calculate recombination factors?

A
  • Calculate total number of flies/ organisms
  • Add the number of observed organism for the two groups you want the distance between
  • Divide this by the total
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44
Q

DEFINITION: Additive map distance

A

When you add together all the recombination factors, not always exactly correct due to double recombinant not always being counted.
To combat this find the square of recombination fraction then subtract from RF

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45
Q

DEFINITION: Loci/ Locus

A

The physical position of a gene or marker along a chromosome

46
Q

DEFINITION: Alleles

A

Different forms of a gene

47
Q

DEFINITION: Polymorphism

A

A gene or phenotype with more than one form

48
Q

DEFINITION: Population Genetics

A

Studies the frequencies of alleles in a population in order to understand

  • forces that determine genetic composition of a population
  • the genetic basis, historical background and carrier frequencies of genetic diseases
49
Q

DEFINITION: Hardy-Weinberg Equilibrium

A

Allele frequencies in one generation can be used to predict genotype frequencies in the next generation

50
Q

Hardy-Weinberg Conditions

A
  • Random Mating
  • No natural selection
  • A large population
  • No mutation
51
Q

Why is Hardy- Weinberg Equilibrium Useful

A
  • Describes how genetic variation is maintained on a mathematic level
  • We can detect and question departures, can identify things acting on population genetics
  • Useful in medical genetics for carrier frequencies
52
Q

DEFINITION: Genetic Migration

A

Introduction of genes from one population to another

53
Q

How to calculate degrees of freedom

A

No. genotypes - No. parameters estimated - 1

54
Q

DEFINITION: Positive Selection

A

When a gene has two alleles, A1 will have a selective advantage over A2 so overtime A1 will increase in frequency, replacing A2

55
Q

HIV

A
  • A pathogen causing AIDs
  • First recognised in 1981 and now up to 42 million infected
  • Single stranded RNA virus
  • HIV makes an enzyme called reverse transcriptase
  • RT converts RNA into double stranded DNA; key step in HIV lifestyle; prerequisite for replication
56
Q

3TC Drug Treatment for HIV

A
  • Interferes with normal reverse transcriptase, blocking HIV production
  • Some strains have developed resistance
  • Mutant RTs have functional defects
  • Reverse transcriptase is error prone so HIV has a high mutation rate
  • Combination therapy combats this
57
Q

Sickle Cell Anaemia

A
  • Recessive disorder caused by a mutation in the B haemoglobin
  • Carriers develop some resistance to malaria as RBC only become sickly when infected
58
Q

Balancing Selection

A
  • Heterozygotes are fitter than homozygotes

- Explains why S Allele is kept at high frequencies in malaria infested parts of Africa

59
Q

Kuru Disease

A
  • Affects the Fore people of Papua New Guinea
  • A Prion Disease similar to mad cow disease
  • Spread by the consumption of prion infected meat
  • Used to take part in cannibalistic rituals which meant this disease spread rapidly
  • Higher levels of resistant gene found in older population born before cannibolism was banned
60
Q

How does habitat destruction affect conservation genetics

A
  • Leads to reduced population sizes which are geographically isolated
  • This leads to genetic drift and inbreeding
61
Q

Genetic Drift

A
  • Loss of genetic variation by chance
  • Loss of variation by drift is increased by small populations
  • Tend to be less polymorphic
  • Alleles drift to fixation and extinction which reduces variation
62
Q

Elephant Seal Genetic Variation

A
  • Only one population of northern seals survived causing a bottle neck
  • N seals had much lower levels of variation than southern seals
63
Q

Mauritius Kestrel

A
  • 1974 bottleneck where only 4 individuals survived
  • Examined genetic markers with micro-satellites
  • Could use samples from museums to compare before and after
64
Q

DEFINITION: Monoculture Effect

A

Concept that genetically homogenous host populations are more vulnerable to infection than genetically diverse populations
Common issue in agriculture

65
Q

Wrights inbreeding Coefficient (f)

A
  • Standard measure of the degree of inbreeding of an individual
  • Two alleles are identical by descent if they trace their ancestry back to the same ancestral allele
  • Calculate the probability that an individual is IBD for locus in question
  • 1 being more inbred
66
Q

Consequences of inbreeding

A
  • Inbreeding depression
  • inbred progeny will have higher f values than outcrossed progeny
  • Higher frequencies of homozygotes in inbred population
  • This reveals recessive disorders and means you’re less likely to benefit from heterozygote advantage
67
Q

Amish people and Genetics

A
  • Small founder population
  • Forbidden to marry outside the community
  • Good genealogical records which are used in pedigrees
  • High incidence of disorders such as dwarfism, polydactyl
68
Q

DEFINITION: Multiregional Model

A

The argument suggesting the transition from H. Erectus to H.Sapiens took place in many places, gene flow between populations

69
Q

DEFINITION: Out of Africa Model

A

Less than 200kya H Sapiens emerged in Africa then spread around the globe, replacing other hominids (H. Erectus)

70
Q

Do Humans have high or low genetic diversity?

A
  • Compared to our nearest relatives we aren’t very diverse

- This supports the Out of Africa Model

71
Q

Are African Populations more diverse?

A
  • African populations have the most variation at most genetic markers
  • Supports out of Africa Model
72
Q

Out of Africa Evidence

A
  • Humans have low genetic variation
  • African populations are most diverse
  • Genetic Distance can be calibrated and time of divergence calculated
73
Q

Two common option for Genetic Markers

A
  1. Mitochondrial DNA

2. Y chromosome DNA

74
Q

Mitochondrial DNA as a genetic marker

A
  • Found in both sexes
  • Maternally inherited
  • Small molecules
  • High mutation rate
  • Many copies per cell
75
Q

Y chromosome DNA as a genetic marker

A
  • Only found in males
  • Paternally inherited
  • Doesn’t recombine with X chromosome
76
Q

Genetic markers in Human Population Genetics

A
  • Autosomes can recombine and create brand new genotypes
  • TMRCA works best with non recombining molecules
  • Used to determine evolutionary relationships between populations, species and sub species
77
Q

Introduction of Agriculture

A
  • Initiated the switch from hunter gatherer lifestyle to living settlements
  • Drove the expansion of the human population
  • Infectious disease rose due to living closely together §
78
Q

Skin Colour adaption

A
  • Determined by melanin
  • Bare skin at risk of damage from UV radiation
  • This leads to sunburn, sweat gland damage, cancers, nutrient photodegradation
79
Q

Dark Skin Benefits

A
  • Live in climates with lots of UV rays as protected

- High vitamin D diet means its OK

80
Q

Light Skin Benefits

A
  • Necessary for Vitamin D production in certain climates, eg Europe
  • UV levels are lower
81
Q

Two types of Melanin

A

Eumelanin- Black/ Brown

Phaeomelanin- Red/ Yellow

82
Q

Adaption to diet across the world

A

Lactose persistence is an adaption

prevalent in European populations where lots of milk in the diet

83
Q

Adaption to disease

A
  • CF most common autosomal recessive disease in Europe

- Some evidence the heterozygotes are resistant to typhoid

84
Q

DEFINITION: Discontinuous Variation

A
  • Discrete classes of phenotype
  • No intermediates
  • Follows mendelian ratios
  • Simple genetic basis, limited effect of the environment
    E.g Blood Group, pea colour
85
Q

DEFINITION: Continuous Variation

A
  • Phenotypes don’t fall into classes
  • Offspring of intermediate phenotype
  • Can’t observe mendelian ratios
  • Complex genetic basis plus effect of the environment
    E.g Height, blood pressure
86
Q

DEFINITION: Normal Distribution

A
  • Fully Described by mean and standard deviation
  • Variance = SD2
  • SD and Variation are measures of spread
87
Q

DEFINITION: Threshold Variation

A
  • Appears to be like a discontinuous trait, but is continuous
  • Distribution called liability
  • Phenotype depends on critical threshold
  • No simple segregation in families
    E.g Diabetes
88
Q

How do genes influence continuous variation?

A
  • More genes means higher variety of possible outcomes
  • There is a relationship between height of brothers but not random people, could be due to same living environment or same alleles
89
Q

Genetic Twin Studies

A
  • Can compare monozygotic and dizygotic twins
  • Both share genes and environments
  • Studies on height revealed it is mostly determined by genes
90
Q

DEFINITION: Phenotypic Variance

A

A measure of the total variation within a population for phenotype
(Vp)

91
Q

What are the two components of Phenotypic Variance

A
  1. Genetic Variance (Vg) due to different genotypes

2. Environmental Variance (Ve) due to environmental effects

92
Q

Broad Sense Heritability Equation

A 
Vp = Vg + Ve
H2 = Vg / Vp
93
Q

Why is heritability only a good predictor for short term responses?

A
  • Allele frequencies change over time due to selection/ genetic drift therefore Vg changes over time
  • Also environement will change over time
94
Q

Genotype- Environment Interaction

A
  • Vp = Vg + Ve + Vgxe
  • Used to consider quantitatively, called norm of reaction
  • Certain genotypes do better or worse in different environments suggesting the presence of an interaction
95
Q

3 requirements for selection

A
  1. Heritable variation
  2. Competition
  3. Fitness/ advantage
96
Q

What limits the reduction of variance when selection is present

A
  1. Mutation
  2. Migration
  3. Different forms of selection
97
Q

DEFINITION: Directional Selection

A

Selection favours an increase in phenotype of interest

98
Q

DEFINITION: Stabilising Selection

A

Individuals with intermediate phenotypes are favoured

99
Q

DEFINITION: Divergent Selection

A

Favours variants of opposite extremes, leads to speciation

100
Q

DEFINITION: Frequency dependence

A

Rare phenotypes might have an advantage, this leads to them becoming more popular and advantage declines

101
Q

Narrow Sense Heritability

A

h2
Proportion of variation that can be passed on to the offspring, more useful as concentrates on addictive genetic variance

102
Q

Broad Sense Heritability

A

H2

Proportion of variation that is due to differences in genotype, usually more than h2

103
Q

Narrow Sense Heritability Equation

A

Change between generations/ Difference between selected group and main group
ie flying speed of drosophila

104
Q

DEFINITION: Biological Species Concept

A

Group of individuals that are reproductively isolated from other groups
Reproductive Isolation is a measurable property of the biology of species

105
Q

Critical Factors for speciation

A
  1. A source of divergent selection

2. A source of reproductive isolation

106
Q

Extrinsic pre mating barriers

A

E.g different pollinators

Some flowers could hybridise but are pollinated by different species pollinators

107
Q

Intrinsic pre mating barriers

A

Different species of crickets have different mating calls so don’t interbreed
Also happens in the lab so no environmental cause

108
Q

Intrinsic post mating barriers

A

E.g 2 types of Drosophila Fly
Diverged due to geographical isolation
Unable to mate and produce fertile females or any males
Due to negative epistasis at 2 locus points

109
Q

Extrinsic post mating barriers

A

E.g Swainson’s thrushes
2 allopatric subspecies with variable hybrids
However use two different routes for migration to avoid hrs climate
Hybrids take intermediate route with low probability of survival

110
Q

Effect of geographic overlap on Speciation

A

A large geographic overlap will have strong homogenising effects of intermixing
A small geographic overlap will reduce gene flow and facilitate emergence

111
Q

Causes of quick speciation

A

Allopolyploidy- multiple chromosome sets derived from different species leads to new species

Ecology & Conservation Year 1 (4 decks)

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