Quantitative Genetics

Question 1

What is quantitative genetics?

Answer 1

genetic traits that vary continuously
weight
height

traits controlled by effects of multiple genes and allele

Question 2

what are the 3 types of polygenic trait?

Answer 2

metric
- continuous scale, no categories

meristic
- discrete scale, counts

threshold
- present ot absent
- need to meet the threshold

Question 3

What are metric traits?

Answer 3

mean = centre of the phenotypic distribution
study of continuously measured traits and their mechanisms

Question 4

what is population variance?

Answer 4

average squared deviation from the mean is called the variance

Question 5

What are meristic traits?

Answer 5

countable structures

Question 6

What are threshold traits?

Answer 6

discrete phenotypes that are multifunctional
e.g. alcoholism, cancer, diabetes

only if reach threshold then you are considered

Question 7

important in medicine?

Answer 7

complex disorders caused by multiple genetic and environmental factors
understanding genetic vs environmental causes

1. prevention
2. genetic counselling
3. genetically tailored treatments

Question 8

important in agriculture?

Answer 8

basis of selective breeding
environmental variation reduces efficiency of selection

Question 9

important in conservation?

Answer 9

of endangered species
of captive breeding programmes
consequences of inbreeding and outcrossing

Question 10

what is the phenotype?

Answer 10

genotype + environment

affected by multiple genes

Question 11

what is variation in a population related to?

Answer 11

phenotypic variance = genetic variance + environmental variance + gene&environment variance

Question 12

what is genetic variance?

Answer 12

contribution to phenotypic variation due to set of alleles present in a population and their interactions

Question 13

what is environmental variance?

Answer 13

contribution to phenotype variation caused by differences in environmental conditions

Question 14

what is broad sense heritability?

Answer 14

measures the importance of genetic variation relative to total variation in the phenotype

Question 15

what is narrow sense heritability?

Answer 15

measures the importance of additive variation or variation doe to the allele present in the population, relative to total variation in causing variation in the phenotype

Question 16

what is h2?

Answer 16

estimates vary substantially across traits, environments and different populations

used to predict change in population means under selection

when it increases, response to selection increases

Question 17

how is heritability measured?

Answer 17

equation of straight-line graph, shows how related the two traits are

y = mx +c

Question 18

How do you estimate adaptive genetic traits?

Answer 18

infinitesimal model

assumes infinite number of unlinked loci, each with infinitesimal effect

infinite number of genes controlling a phenotypic trait each with a very small effect

Question 19

what does the population genetic theory state?

Answer 19

frequencies of alleles and genotypes in a population remain constant unless acted upon by non-mendillian processes

equilibrium = no evolution

Question 20

what is p in hardy Weinberg?

Answer 20

p = frequency of one allele in the population

(study 2 alleles in locus)

Question 21

what is q in hardy Weinberg?

Answer 21

frequency of the other allele in population

Question 22

What is the hardy Weinberg equation?

Answer 22

p2 + 2pq + q2 = 1

p2 = proportion of population that is homozygous for first allele
2pq= proportion of population that is heterozygous
q2= proportion of population that is homozygous for second allele

Question 23

When does hardy-weinberg apply?

Answer 23

when organisms are diploid
allele frequencies same in each sex
mendelian segregation occurs
mating occurs at random
population size is large so no genetic drift
no gene flow
no mutation
no selection

Question 24

1. population size so large so no genetic drift

Answer 24

mainly affects smaller populations
drift = allele frequency change
reduces genetic variation

Question 25

2. no migration or gene flow

Answer 25

migration transfers individuals amongst populations
gene flow transfers alleles amongst populations, increase or decrease

Question 26

3. no mutation

Answer 26

mutations increase variation

Question 27

4. no selection

Answer 27

biases which genotypes transmitted to next generation
increase or decrease variation
operate many different ways

Question 28

What is linkage disequilibrium?

Answer 28

non-random association between two polymorphic loci