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Nature via Nurture > MCQ > Flashcards

MCQ Flashcards

1
Q

BROAD-SENSE HERITABILITY

A

H2 = VG/(VG+VE)

V = variance, G = genotype, E = environment…..

G includes additive genetic variance (allelic differences), dominance effects (vs. recessive), epistasis (G*G interactions) & parental effects

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2
Q

NARROW-SENSE HERITABILITY

A

h2 = VA/(VA+VE)

VA = additive genetic variance

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3
Q

Problems measuring heritability

A
  1. You need intra-specific variation (some traits cannot be measured)!
  2. It depends on the environmental variation
  3. Does not explain means but variance
  4. Female choice and the lek paradox:
    constant selection on genes should reduce genetic variation, heritability and evolution →dominant role of nurture!
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4
Q

Introns & Exons

A

Exons: coding region

Introns:
region that is not translated into protein
transcribed to precursor mRNA and then removed by splicing during processing to mature RNA

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5
Q

Mutations in mitosis

A

little effect

increase with age

70% harmful

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6
Q

Mutation in meiosis

A

greater influence as only one cell

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7
Q
  1. Crossing over/ recombination
A

essential and facilitated by Spo11 protein which initiates double-stranded breaks

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8
Q
  1. TRANSCRIPTION
A

create a complementary RNA copy of a sequence of DNA

  • If gene → protein, then RNA is a messenger RNA (mRNA)
  • Else ribosomal RNA (rRNA), transfer RNA (tRNA) or ribozymes…
  • RNA Polymerase produces complementary, antiparallel RNA strand
  • Polymerase binds onto core promoter in the presence of transcription factors → initiation of transcription
  • Only some genes are transcribed in each cell
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9
Q
  1. mRNA SPLICING
A

remove introns and join exons

  • Spicing generally an action of proteins – interestingly, they can do this in various ways (moving exons around, deleting them, sometimes including introns)
  • Number of introns per gene increases roughly with complexity, humans have 100s or 1000s / gene
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10
Q
  1. TRANSLATION
A

create a chain of amino acids from mRNA

  • occurs across the membrane of the endoplasmic reticulum
  • ribosome facilitates decoding by inducing the binding of tRNAs with complementary anticodon sequences to that of the mRNA
  • amino acids are attached to tRNA and are joined together by the ribosome
  • Make millions of different proteins
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11
Q

Waddington 1942 definition of epigenetics

A

The interaction among genes and between genes and environment that lead to a given development and bring the phenotype alive

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12
Q

Nanney 1958 definition of epigenetics

A

Mechanisms of inheritance that do not include the DNA sequence

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13
Q

nucleosome

A

subunit of chromatin composed of a 147 BP length of DNA wrapped around a core of histone proteins

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14
Q

Chromatin

A

a complex of DNA and protein in eukaryotic cells

changes in chromatin structure affected mainly by methylation and acylation of the nucleosome proteins

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15
Q

4 DIFFERENT WAYS TO INFLUENCE GENE EXPRESSION

A
  1. Make the DNA unable to bind RNA transferase (DNA methylation & Gene Switches)
  2. Make the DNA inaccessible and/or impossible for proteins to bind (Histone Modification & Chromatin Remodelling
  3. Alternative Splicing the introns and exons to create alternative proteins
  4. Disrupt translation to influence protein production
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16
Q

DNA METHYLATION

A
  • de novo methyltransferases (enzymes) add methyl groups to CpG sites
  • this prevents protiens binding to promoter region in DNA
  • gene is silenced
  • only occurs in totipotent stage of embryogenesis
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17
Q

DNA METHYLATION: Horizontal Memory

A
  • In mitosis
  • maintenance methyltransferase copies over methylation patterns
  • →life-long effects of patterns that were established at birth
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18
Q

DNA METHYLATION: Vertical Memory

A
  • paternal genome actively demethylated few hours after fertilization
  • maternal genome passively demethylated during early embryogenesis (no maintainance methyltransferase)
  • remethylation occurs at implantation
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19
Q

nucleosome

A

subunit of chromatin composed of a short length of DNA wrapped around a core of histone proteins → allows compaction of DNA by sixfold

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20
Q

Euchromatin

A

lightly packed form of DNA, regions rich in genes → often under active transcription

21
Q

Heterochromatin

A

tightly packed form of DNA, repetitive sequence and regions with few protein coding genes → non-transcribed = silenced

22
Q

Histone Modification

A
  • post-translation
  • tails of histones (H3 and H4)
  • modifications such as: methylation (can be repression as well as activation), acetylation & phosphorylation
  • can effect: gene expression, DNA repair & chromosome condensation
  • horizontal transmission, dont know about vertical
  • patterns vary from one organism to the next
23
Q

3 main functions of histone modification

A
  1. alter chromatin structure & weakens or fastens grip on DNA
  2. inhibit or facilitates binding of transcription factors and other enzymes
  3. creates binding site for particular protein
24
Q

possibilities for alternative splicing

A
  • Exon skipping : exon may be spliced out of the primary transcript or retained (most common in mammals)
  • Mutually exclusive exons: only one of two exons is retained in mRNAs after splicing.
  • Intron retention: an intron may or may not be spliced out
25
Q

How is alternative splicing regulated?

A

A system of trans-acting proteins that bind to cis-acting sites on the pre-mRNA

  • Splicing repressors, bind to silencers, ↓ probability that a nearby site used as splice junction
  • Splicing enhancers, bind activators = ↑ probability that a nearby site used as splice junction
26
Q

miRNA

A
  • ~22 bp long
  • bind to complementary mRNA areas
  • →post-transcription gene silencing
  • pivotal in evolution of complexity? by causing innovations?
27
Q

In all species DNA methylation patterns are..

A
  1. dynamic
  2. variable amond individuals
  3. conserved within species
28
Q

Genomic Imprinting

A

Silencing of one parental copy of each gene, which depends on the sex of the parent from which it was inherited.

non- random silencing

not 50:50 inheritance

why? paternal genes take resources from mother at her expense, benefits genes to know where they come from

29
Q

Mechanisms by which early enviroment can affect adulthood health

A
  • Thrifty Phenotype
  • Maternal effects
  • Predictive adaptive responses
  • Matching
30
Q

Why is early environment associated with adult disease?

Genetic effects?

A

not selected against as did not reduce fitness? (pre-industrial when people dies younger)

WRONG

31
Q

Why is early environment associated with adult disease?

Correlation between birth and adult environment ?

A

People who were deprived in early life were also deprived in later life

WRONG

32
Q

Why is early environment associated with adult disease?

Long-term effects of early environment ?

A

Cohort effects or maternal effects on intrauterine growth, with downstream effects on adult phenotype

YES

nutrient avalibility affects hormonal control

leads to long term changes

33
Q

Why does experience in early development permanently affect metabolic function?

A
  1. The 1992 thrifty phenotype hypothesis
  2. Thrifty phenotype as an adaptive maternal effect
  3. The predictive adaptive response (PAR) hypothesis 4. Matching between maternal and offspring phenotype
34
Q

The 1992 Thrifty Phenotype Hypothesis

Hales & Barker

A

“We propose that type 2 diabetes is the outcome of the fetus having to be nutritionally thrifty”

i.e. fetus changes structure and function of tissues because they help it to cope with a reduced nutrient supply there and then

Developing slowly and being small at birth is better than dying !

35
Q

Thrifty phenotype could be an adaptive maternal effect

Hales & Barker 2001

A

“The poorly nourished mother gives the fetus a forecast of its post-birth nutritional environment. The adaptations only become detrimental when the postnatal environment and mother’s forecast differ”

i.e. fetus changes structure and function of tissues because they help it to cope with a reduced nutrient supply in the short-term future

36
Q

The predictive adaptive response (PAR) hypothesis

Gluckman & Hanson 2004/2005

A

“PARs are induced by environmental factors acting in early life, not as an immediate physiological adaptation, but as a predictive response to expected future environment”

“The induction of PARs will confer a survival advantage in the predicted reproductive enviroment”

i.e. fetus changes structure and function of tissues because they help it to cope with a reduced nutrient supply in the long-term future

37
Q

adaptive value of insulin resistance in PAR hypothesis?

A

Reduces energy invested into growth and metabolism

38
Q

adaptive value of Reduced skeletal muscle mass in PAR hypothesis?

A

Decreases energetic demands of maintaining adult body and frees up resources for survival and reproduction

39
Q

adaptive value of Reduced negative feedback in the HPA axis in PAR hypothesis?

A

Heightened stress response allows greater chance of survival in a nutrient-deprived and predator rich environment

40
Q

Support for PAR

A
  • Meadow voles: Mothers ‘predict’ thermal environment that offspring will eventually live in
  • Dutch famine: short, mismatch, adults have impared glucose tolerance. Siege of Leningrad: long, match, no impared tolerance
41
Q

Problems with PAR hypothesis

A

things can change in lifetime!

42
Q

Matching between maternal and offspring phenotype

Wells 2007

A

“The thrifty phenotype has been favoured due to its capacity to improve the fit between offspring and maternal phenotypes, and represents a mechanism to maximise maternal, rather than offspring, fitness”

i.e. fetus changes structure and function of tissues so that its metabolic demands will match that which its mother can provide

43
Q

Environmental ‘matching’ predictions of the different hypotheses

A
44
Q

Silver spoon

A
  • no matching- fitness always improves with enviroment
  • those born in good cond. always do better
  • evidence: choughs
45
Q

how to Conduct Experiments to test PAR

A
  • Chose your metric of early condition (food, density, competition, predation)
  • Notice, most studies either increase or decrease ingredients, not both…think of Dutch and Leningrad famines. Can you manipulate both?
  • How does your experiment isolate your ingredient, without impacting other possible ingredients?
46
Q

Why Should Phenotypes Be Plastic?

A
  • Efficient allocation of nutrients and energy
  • Traits can be costly when not needed
  • Consequences of having traits when needed are predictable
  • Needs are unpredictable in time and space, plasticity allows adaptation when/where needed?
47
Q

problems with the modern synthesis

A
  • How do plastically complex traits arise from genes selected for a given trait get constructed during evolution?
  • How does genetic responses to environment evolve

poly-modality

If random mutation and selection represent the main evolutionary driver, how can big changes in phenotype evolve so quickly? And how can you get big differences in phenotype without differences in genotype?

•the lack or constraining force of development

48
Q

extended synthesis

A

Natural selection can only affect genes that are expressed and have measurable phenotypic consequences. Genes that are not expressed or are phenotypically neutral have their own evolutionary rhythm. Suggests that selection acts on phenotypes not genes (ie outcomes not input).

49
Q

Genetic assimilation

A

the introduction of beneficial genes into existing selection on phenotypes arises through developmental canalization (selection on a single outcome)

Nature via Nurture (1 decks)

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