Quantitative genetics

Question 1

discontinuous (qualitative) traits

Answer 1

can be categorised into few classes
exhibit only a few, easily distinguished phenotypes

Question 2

continuous (quantitative) traits

Answer 2

vary along a scale of measurement
exhibit continuous range of phenotypes

Question 3

bimodal distribution (polyphenism)

Answer 3

two peaks

Question 4

meristic traits

Answer 4

determined by multiple genetic and environmental factors
can be measured in whole numbers

Question 5

threshold traits

Answer 5

measured by presence or absence
eg susceptibility to disease

Question 6

polygenic traits

Answer 6

phenotype reflects cumulative effects of many genes/loci
influenced by many environmental factors
lots of different genotypes can produce the same phenotype

Question 7

phenotypic variance

Answer 7

total amount of variation among individuals in some trait

Question 8

equation for phenotypic variation

Answer 8

Vp=Vg+Ve+Vge
where g=genetic variance
e=environmental variance
ge=genotype-environment interaction variance

Question 9

equation for genetic variance

Answer 9

Vg=Va+Vd+Vi
where a is additive/heritable variance that contributes to parent-offspring inheritance
d= dominance variation (non heritable)
I= is genetic interaction/epistatic variance (non heritable)

Question 10

inherited

Answer 10

dna sequences passed from parents to offspring (chromosomes, mitochondria etc)

Question 11

heritable

Answer 11

phenotypic trait differences of individuals reflect genetic differences between individuals
contributes to parent offspring resemblance

Heritable traits refer to characteristics that have a genetic basis and

Question 12

narrow sense heritability

Answer 12

the proportion of phenotypic variation that contributes to the resemblance between parents and offspring
(additive genetic)

Question 13

broad sense heritability

Answer 13

proportion of phenotypic variation attributable to all types of genetic differences between individuals

Question 14

equation for narrow sense heritability

Answer 14

h^2=additive genetic variance/phenotypic variance

Question 15

equation for broad sense heritability

Answer 15

H^2= genetic variance/phenotypic variance

Question 16

regression (to measure narrow sense heritability)

Answer 16

predicting the value of one variable if the other value of the other is given

Question 17

regression coefficient

Answer 17

represents the slope of the regression line, indicating how much one value changes on average per increase in the value of another variable
gives you the narrow sense heritability

Question 18

genotype-by-environment interaction

Answer 18

the phenotypic difference between genotypes depends on the environment they experience

Question 19

what causes correlation between traits

Answer 19

environmental correlation
genetic correlation (due to pleiotropy or linkage disequilibrium)

Question 20

phenotypic vs genetic correlations on graphs

Answer 20

point are different individuals-phenotypic
points are average values for different genotypes=genetic correlation

Question 21

pleiotropy

Answer 21

variation at a single locus leads to variation in multiple traits

Question 22

linkage equilibrium

Answer 22

combinations of alleles at the A and B loci should be randomly assorted
expect equal frequencies of coupling and
repulsion gametes

Question 23

linkage disequilibrium

Answer 23

occurs when there is an association between alleles at different loci.
if you know the allele present at one locus you can predict the allele at the other locus because they are inherited/ co vary.
not same as physical linkage
there is an overrepresentation of coupling gametes or repulsion
gametes

Question 24

epistasis

Answer 24

occurs when the effect of alleles at a
locus depends on alleles present at other loci
appearance of interaction depends on the variation at each locus

Question 25

linkage equilibrium equation, eg for AB

Answer 25

F(AB)=px where p=F(A) and x=F(B)

Question 26

linkage disequilibrium equation

Answer 26

(product of frequency of coupling combinations)-(product of frequency of repulsion combinations)

Question 27

effect of recombination on LD

Answer 27

breaks up associations between alleles-removes LD rate of recombination determines how quickly LE is restored

Question 28

what is a quantitative trait locus (QTL)

Answer 28

a location in the genome that causes different values of the trait in question (that position in the genome is associated with differences in the phenotype)

Question 29

what is genome wide association study

Answer 29

identifies loci associated with trait variation, usually in natural populations

Question 30

equation for overall phenotypic variation, taking into account heritable and non heritable genetic and environmental origins of variation

Answer 30

Vp=Va+Vd+Vi+Ve+Vge

Question 31

genotypes generally do not produce distinct phenotypes because of...

Answer 31

codominance incomplete dominance epistasis polygenic inheritance environmental influence recessive traits

Question 32

trade offs

Answer 32

can be shown by correlations an organism can do one thing well but at the detriment of another thing eg making lots of small seeds or fewer large seeds

Question 33

positive linkage disequilibrium

Answer 33

more coupling gametes

Question 34

how does linkage disequilibrium lead to correlation, using height and foot size as an example

Answer 34

Imagine the A locus affects height and the B locus affects foot size. Assume that the large alleles (A and B) lead to larger size than the small alleles (a and b) If there is an excess of coupling gametes, individuals will tend to inherit A with B and a with b, leading to a correlation between height and foot size

Question 35

locating loci that affect quantitative characteristics

Answer 35

mapping QTLs genome wide association studies

Question 36

a QTL can be caused by differences in

Answer 36

coding regions regulatory elements do not often reflect changes to protein produced as can be caused by non coding differences more often associated with differences in gene expression

Question 37

QTL analysis

Answer 37

uses genetic markers to test whether different genotypes have significantly different trait values (phenotypes)

Question 38

genetic markers

Answer 38

any type of variable locus where alleles can be distinguished identify casual variation linked to these markers (co inherited with casual alleles)

Question 39

Heritability refers to the proportion of phenotypic variation in a population that is attributable to genetic variation. When narrow sense heritability equals 1, it means that all phenotypic variation is due to additive genetic factors, making the trait highly predictable based on the genotype. Inherited traits are characteristics passed from parents to offspring through genes. All heritable traits are inherited, but not all inherited traits are perfectly heritable (i.e., heritability = 1).