Genotypic value is not transferred from parent to offspring; genes are.

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Genotypic value is not transferred from parent to offspring; genes are. eed a value that reflects the genes that an individual carries and passes on to it’s offsprin irically: An individual’s value based on the mean deviation of its p m the population mean. oretically: An individual’s value based on the sum of the average ef the alleles/genes it carries. Breeding Value

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Genotypic value is not transferred from parent to offspring; genes are. Need a value that reflects the genes that an individual carries and passes on to it’s offspring. Breeding Value. Empirically : An individual’s value based on the mean deviation of its progeny - PowerPoint PPT Presentation

Transcript of Genotypic value is not transferred from parent to offspring; genes are.

Page 1: Genotypic value is not transferred from parent to  offspring; genes are.

Genotypic value is not transferred from parent to offspring; genes are.

Need a value that reflects the genes that an individual carries and passes on to it’s offspring

Empirically: An individual’s value based on the mean deviation of its progenyfrom the population mean.

Theoretically: An individual’s value based on the sum of the average effectsof the alleles/genes it carries.

Breeding Value

Page 2: Genotypic value is not transferred from parent to  offspring; genes are.

average effect of An:

n = mean deviation from the population mean of individuals that received An from one parent, if the other parent’s allele chosen randomly

1 = q [ a + d (q – p)]

2 = –p [ a + d (q – p)]

1 = pa + qd - [ a (p – q) + 2dpq ]

population mean.

f (A1) f (A2)

Average Effect of an Allele

Type of Values and Freq Mean value Population Average gamete of gametes of genotypes mean effect of

geneA1A1 A1A2 A2A2

a d -a

A1 p q pa + qd -a(p-q) + 2dpq q[a+d(q-p)] A2 p q -qa + pd -a(p-q) + 2dpq -p[a+d(q-p)]

Page 3: Genotypic value is not transferred from parent to  offspring; genes are.

When there are only two alleles at a locus

A1A1 A1A2+a d

A2A2-a

Average effect of a gene substitution

(a - d) (d + a)

p(a - d) + q(d + a)

= a + d(q - p)

p

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Frequency q (A2 orTH2)

0.0 0.3 0.5 0.7 1.0

: TH1 0 9.3 12.5 13.3 10

:TH2 -40 -21.7 -12.5 -5.7 0

4031 251910d = -15; a = 25

Average Effects

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Genotype Breeding Value

A1A1

A1A2

A2A2

21 = 2q

1 + 2 = (q - p)

22 = -2p

Theoretically: An individual’s value based on the sum of the average effects of the alleles/genes it carries.

Page 6: Genotypic value is not transferred from parent to  offspring; genes are.

Breeding Values - TH example

A2 or Th2 Pop Mean A1A1 A1A2 A2A2

q = 1.0 150 20 20 0

q = 0.7 158.7 26.6 15.2 -11.4

q = 0.5 167.5 25 0 -25

q = 0.3 178.7 18.6 -24.8 -43.4

q = 0.0 200 0 -80 -80

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Sum of average effects across loci

Breeding Value

(A)=

G = A + D

Genotypic Value = Additive effects

of genes + Dominancedeviation

A1A1 A1A2 A2A2

21 1 + 2 22(breeding values)

+B1B1 B1B2 B2B2

21 1 + 2 22(breeding values)

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Partitioning the phenotypic value

P = G

P = A1 + D1 + A2 + D2 + I12

phenotypic value of individual

genotypic value of individual

G = A + D

breeding value

dominancedeviation

G = G1 + G2 + I12

interaction

two-locus:

genotypic value

breedingvalue

geno

typi

c va

lue

deviations from population m

ean

d=3/4a, q = 1/4

Pop Mean

Page 9: Genotypic value is not transferred from parent to  offspring; genes are.

Environmental effects on phenotypes

P = A + D

One locus, two alleles

One locus, two alleles + environmental variation

environmentaldeviation

P = A + D + E

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Amount of genetic variation in a population depends on# of genotypes, genotypic value, and gene frequencies.

p = 0.5 p = 0.9

A1A1 A1A2 A2A2 A1A1 A1A2 A2A2

0.75

0.50

0.25

0.75

0.50

0.25

Mean Mean

9 10 11 9 10 11

More variation Less variation

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Components of phenotypic variation

P = A + D + I + E

VP = VG + VE

Variance partitioning:

totalphenotypic

variance

additivegenetic

variance

dominancegenetic

variance

interaction(epistatic)

geneticvariance

environmentalvariance

VP = VA + VD + VI + VE

.

• Phenotypic variation can be decomposed into additive genetic and other variation• Relative contributions of different sources depend on allele frequencies

V

f (A1)

a = d = 0.07

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Genotypic, VG

Additive, VA

Dominance, VD

q = 0.3

443.31

403.62

39.69

q = 0.7

191.24

151.62

39.69

VA = 2pq[a + d (q - p)]2 VD = (2pqd)2

d = -15; a = 25

TH alpha Example

(178.7) (158.7)

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Environment and genotype can interact

VP = VA + VD + VI + VE

Different environmental effects across genotypes result in G x E interaction variance

VP = VA + VD + VI + VE + VGxE

genetic xenvironmental

interactionvariance

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h2 = VA/Vp

Expresses the extent to which genes are transmitted from parents to offspring

Proportion of total phenotypic variance attributed to variation in breeding values.

Heritability

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Resemblance between parents and offspring indicates degree to which a trait is inherited

heritability (narrow sense):

h2 = VA

VP

h2 = bOP

• heritability can also be estimated with offspring–midparent regression

Drosophila wing length

offs

prin

g (O

)

bOP

parental average (P)

Detecting the genetic componentof phenotypic variation

Fraction of variation in parents that is explained by variation in their genes (VA).

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19761978 h2 = 0.9

Bill depthin the

Ground Finch

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Almost all characteristics in almost all species are genetically variable to some extent.

Heritability is often measured in the lab; estimates are higher than would be expected in nature.