Quantitative Genetics

Question 1

What is quantative genetics about?

Answer 1

The Genetic Basis of Complex Inheritance

Question 2

Complex inheritance

Answer 2

traits that have a genetic component that does not follow strict Mendelian inheritance (relationship between genotype and phenotype)
Instead it’s the quantity of phenotype that differs rather than the type

Question 3

What are complex traits known as?

Answer 3

Quantitative traits as they are often measured

Question 4

Examples of complex traits/inheritance

Answer 4

Adult weight, height, blood pressure, insulin resistance, milk yield, meat production, weight gain

Question 5

What is genetics of quantitive traits often referred to as?

Answer 5

Polygenic

Question 6

Polygenic meaning

Answer 6

More than 1 gene involved

Question 7

– A single genotype can have…
– A single phenotype can result from…

Answer 7

Many phenotypes
Many genotypes

Question 8

2 contributing factors to quantative traits=

Answer 8

Genotype- many genes
Environmental factors

Question 9

Examples of environmental effects influencing genes involved in traits

Answer 9

-weight is influenced by prenatal and childhood nutrition
-congenital hip dysplasia is influenced by the position of legs in utero

Question 10

Formula of quantitative traits

Answer 10

P=G+E

Phenotype = genetics plus environment

Question 11

What is continuous distribution/variation

Answer 11

Constantly seeing distribution of a specific trait; its showing continuously with changing quantity of it
(Graph on anki)

Question 12

What are discontinuous traits

Answer 12

Single gene disorders where animals is either affected or not; not a measureable trait

Question 13

In what ways does the action of genes and the environment result in continuous variation?

Answer 13

1. Additive gene action

Question 14

Additive gene action
-what is it
-effect is…
-what does it result in?

Answer 14

Each allele at a given locus (location) has a specific value that it contributes to the phenotype
-effects are additive (cumulative)
-results in each gene having a slightly different quantitive value

Question 15

In additive gene action, alleles contributing to a single phenoytpe results in…

Answer 15

Huge variation which gives rise to continuous distribution

Question 16

What is additive variation responsible for?

Answer 16

Resemblance between parents and offspring- heritability

Question 17

What are the 3 types of gene action in high genes that can interact in complex gene disorder?

Answer 17

1. Additive gene action
2. Dominance gene action
3. Epistasis gene action

Question 18

What is dominance gene action
-not always…

Answer 18

• one allele dominant over another; homozygous dominant will have same phenotype as heterozygous
  -not always inherited

Question 19

What is Epistasis gene action

Answer 19

Presence of one gene affects another gene

Question 20

Describe an example of Epistasis gene action

Answer 20

Coat colour of dogs controlled by 2 genes;

Gene 1-> codes for coat colour
B allele= dominant (black)
b allele= recessive (brown)

Gene 2-> codes for expression of pigment
E allele= allows pigment expression
e allele= no pigment expressed

Mixes of these will give different variations of coat colour of dog eg BbEe=black, bbEe= brown, Bbee= white

Question 21

Threshold traits

Answer 21

Threshold traits refers to traits that you would at first assume are discontinuous, however on a graph are depicted by increasing liability of getting the disease for example hip dysplasia or diabetes. Individuals with a liability above threshold develop the trait
(Graph on anki)

Question 22

Heritability
-what is it
-2 types

Answer 22

the portion of the phenotypic variation VP due to
genotypic variation VG (genetics)

-broad sense heritability
-narrow sense heritability

Question 23

Broad sense heritability

Answer 23

How much of genetics is responsible for the phenotype

H^2=Vg/Vp

H=heritability
Vg=genotypic variation
Vp=phenotypic variation

Question 24

Narrow sense heritability
-formula

Answer 24

h^2=Va/Vp

(Va=additive variation)

Question 25

If a trait has a large genetic contribution, then…

If a trait has a low genetic contribution, then…

Answer 25

-trait can be selected for

-more beneficial to alter environmental conditions

Question 26

What is the heritability value scale?

Answer 26

0:1

0 means no differences in trait are due to genetic factors (no genetic factors)
1 means all differences in trait are due to genetic factors

Question 27

3 steps to measuring heritability
-heritability for weight in sheep

Answer 27

1. Measure the phenotypic variation (weight) of a large flock of sheep
2. The sheep are then allowed to mate and when the lambs grow up, their weights are measure
3. The offspring weights (phenotypic values) are plotted against the mid parent weights (mid-parent offspring regression analysis).

Question 28

What are Quantitative Trait Loci (QTLs)

Answer 28

Stretches of DNA that contain genes that are linked to quantitative traits

Question 29

What is genetic selection used for?

Answer 29

Improving livestock traits;

– milk production,
– rapid growth,
– leanness,
– high meat production,
– more eggs
– higher fecundity

Question 30

What can genetic overselection do?

Answer 30

Can compromise animal welfare eg double muscling in cattle

Question 31

Formula for genotypic aviation
VG=…

Answer 31

VG = VD + VI + Va