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BIO1334 Genetics > Human Molecular Genetics > Flashcards

Human Molecular Genetics Flashcards

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1
Q

Which scientist linked a wide range of cancers to chemicals found in our environment?

A

Sir Richard Doll.

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2
Q

Give the definition of a monogenic disease.

A

Usually rare and caused by loss or gain of function mutations in protein-coding genes. Can be dominant, recessive or X-linked.

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3
Q

How do we know if common traits have a genetic component?

A
  • twin, family and admixture studies have suggested that type 2 diabetes has a genetic component.
  • in twins, monozygotic twins are 40% more likely to have type 2 diabetes if the other twin has it.
  • in families, risk of type 2 diabetes in sibling of affected person is 3-4x greater than the general population risk.
  • population, European admixture lowers diabetes risk in Nauruans (17% vs 83%)
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4
Q

Give all the modes of inheritance.

A 
Dominant
Recessive
Autosomal recessive
Autosomal
X-linked recessive
X-linked dominant
Mitchondrial
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5
Q

Patterns found in dominant inheritance.

A

Vertical patterns of affected individuals.

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6
Q

Patterns found in recessive inheritance.

A

Horizontal patterns of affected individuals.

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7
Q

Patterns found in autosomal recessive inheritance.

A

Consanguinity often present between parents.

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8
Q

Patterns found in autosomal inheritance.

A

Males & females affected with equal probability.

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9
Q

Patterns found in X-linked recessive inheritance.

A

Males affected, female carries.

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10
Q

Patterns found in X-linked dominant inheritance.

A

All daughters of affected males are affected.

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11
Q

Patterns found in mitochondrial inheritance.

A

Non-Mendelian, maternal inheritance.

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12
Q

Give the complications that effect interpretation of pedigrees.

A
  • new mutations
  • penetrance
  • expressivity
  • delayed onset
  • anticipation
  • imprinting
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13
Q

Describe how to identify a disease gene.

A
  • simple protein involved > mRNA/cDNA > gene

- map to chromosomal locus (positional cloning)

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14
Q

Describe how genetic linkage allows disease genes to be mapped.

A
  • measured from recombination frequencies between 2 markers in crosses
  • humans are not ideal for this
  • molecular or phenotypic markers allow mapping
  • molecular markers eg structural rearrangements, SNPs, RFLPs, INDELS, copy no. variations eg VNTRs with multiple alleles
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15
Q

Describe genetics linkage analysis, Logs Odd Scores.

A
  • use stats analysis
  • lod score = log10 (odds loci are linked/ odds loci are unlinked)
  • lod scores are logarithms so data from different families can be pooled from different pedigrees by adding log scores
  • lod score > 3.0 indicates likelihood of observing the given pedigrees if the 2 loci are not linked is less than 1 in 1000. (ie they are because without linkage seeing the same pattern in both would be very unlikely)
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16
Q

Why has GWAS facilitated large progress in identifying common diseases?

A

We can study a large proportion of the common human variation in one experiment.

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17
Q

Why can increased incidence of obesity (and diabetes) not be 100% due to changing genes or environment?

A
  • we can say that the obesity epidemic is 100% environmental and 0% genetic
  • EXCEPT twin studies have shown that there is a genetic component, while BMI has increased as a result of changing environments, where you sit in that distribution is determined by >50% of your genetics.
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18
Q

Give the definition of quantitative traits.

A

Traits that vary continuously

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19
Q

Give the function & types of quantitative traits

A
  • controlled by the effects of multiple genes & alleles

- polygenic, multifactorial, multilocus

20
Q

Give the 3 different types of polygenic trait.

A
  • metric, continuous scale
  • meristic, discrete scale
  • threshold, present or absent
21
Q

What are all the types of polygenic trait based on?

A

All are based on the theoretical assumption of an underlying normal distribution

22
Q

Give the graph shape for metric traits.

A
  • bell curve
  • mean is the centre of the phenotypic distribution
  • population variance is the average squared deviation from the mean
23
Q

Give the graph shape for meristic traits.

A

-normal distribution but just not as smooth as typical bell curve

24
Q

Give the graph shape for threshold traits.

A
  • discrete (present or absent) & multifactorial, only reach a threshold when you’ve reached a certain level
  • normal distribution
25
Q

Give some examples of the importance of quantitative genetics.

A

Medicine
- susceptibility to disease, complex disorders cause by multiple genetic & environmental factors, understanding genetic vs environmental causes
-prevention > genetic counselling > genetically tailored treatments
Agriculture
-economically important traits = qualitative traits
-basis for selective breeding
-environmental variation reduces efficiency of selection
Conservation
-endangered species
-captive breeding programs
-consequences of inbreeding & outcrossing

26
Q

Are QTs fundamentally different from the Mendelian patterns of inheritance?

A

NO, traits are still determined by alleles of genes that are inherited following the laws of segregation and independent assortment.
BUT we must consider traits that are influenced by genes and the environment.

27
Q

Give the equation when the variation we see in a population is related to genetic, environmental & G*E interaction variance.

A

V^p = V^g + V^e + V^ge

28
Q

Explain broad sense heritability.

A

Measures the importance of genetic variation in relation to total variation in the phenotype.
How much is related to genetics & how much is related to the environment.

29
Q

Explain narrow sense heritability.

A

Measures the importance of variation due to the alleles present in the population, relative to the total variation in causing variation in the phenotype.
How much is additive and how much is environmental.

30
Q

Theoretically h^2 values should be between…

A

0 & 1.

31
Q

What does h^2 predict?

A

Change in the population mean under selection.

32
Q

When h^2 increases, the response to selection…

A

also increases.

33
Q

What is the infinitesimal model?

A
  • simple model of the inheritance of quantitative traits, which assumes an infinite no. of unlinked loci, each with and infinitesimal effect.
  • infinite no. of genes controlling a phenotypic trait with a very small effect.
34
Q

What does equilibrium mean for evolution?

A

No evolution.

35
Q

Give the population genetics theory.

A

the frequencies of alleles & genotypes in a population will remain constant unless acted upon by non-Mendelian processes.

36
Q

How did Theodosius Dobzhansky define evolution?

A

‘a change in the frequency of an allele within a gene pool.’

37
Q

What does the Hardy-Weinberg equilibrium test?

A

Whether a population has evolved or not.

38
Q

Hardy-Weinberg only applies when…

A
  • organisms are diploid, sexual & have discrete generations
  • allele frequencies are the same in each sex
  • Mendelian segregation occurs
  • mating occurs at random
  • population size is large and there is no genetic drift
  • no gene flow (immigration/emigration)
  • no mutation
  • no selection
39
Q

How does selection influence population genetics?

A

Biases which genotypes are transmitted to the next generation
Can either increase or decrease genetic variation depending on type of selection
Can operate in many different ways

40
Q

How does mutation influence population genetics?

A

Increase genetic variation
Create dominant, recessive or co-dominant
Can be harmful, neutral or favourable
Effect depends on environment

41
Q

How does genetic flow influence population genetics?

A

Migration transfers individuals amongst populations
Gene flow transfers alleles amongst populations
Can increase or reduce genetic variation

42
Q

How does a small population influence population genetics?

A

Genetic drift affects smaller populations the most
Allele frequency changes due to chance because of a sampling error
Genetic drift reduces variation

43
Q

How does non-random mating influence population genetics?

A

Non-random mating does not change allele frequencies but does change how the alleles are distributed into diploid genotypes.
eg assortative and disassortative mating & inbreeding.

44
Q

Describe the effect of positive assortative mating.

A

produces few AA x aa matings so

  • increase in homozygous individuals
  • decrease in heterozygous individuals
45
Q

What is linkage disequilibrium?

A

non-random association between 2 polymorphic loci

46
Q

Under HWE the frequency of a given haplotype =

A

frequency of each allele multiplied together.

BIO1334 Genetics (15 decks)

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