Chapter 11 Molecular Mechanisms of Gene regulation Jones and Bartlett Publishers © 2005.
© 2006 Jones and Bartlett Publishers Chapter 15Complex Inheritance 15.1quantitative traits...
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Transcript of © 2006 Jones and Bartlett Publishers Chapter 15Complex Inheritance 15.1quantitative traits...
© 2006 Jones and Bartlett Publishers
Chapter 15 Complex Inheritance
15.1 quantitative traits15.2 gene/environment interactions15.3 artificial selection
Up until now…traits have been discrete
either round or wrinkled,either yellow or green,red eyes or white eyes,…
a single gene has different alleles having different phenotypes
very easy to study and understand
But many traits are the result of interactions between multiple genes as well as being affected by the environment
The traits are called:
multifactorial traitsquantitative traits
multifactorial traitsquantitative traits
influenced by:
alternative genotypes of one or more genes
environmental factors
inbred lines
© 2006 Jones and Bartlett Publishers
Fig. 15.1. A completely inbred line is homozygous for every gene
multifactorial traitsquantitative traits
influenced by:
alternative genotypes of one or more genes
environmental factors
example height
continuous traitsheight, blood pressure, weightcrop yield, milk production
categorical traitsears of corn/stalkeggs from henridges in fingerprints
threshold traitsfew phenotypesmultiple genes/environement“predisposition to express”
continuous traits
“discrete” traits
like seed color75% yellow, 25% green
like heightdistributions
mean, variance (std. deviation)
Quantification (how do we describe the results)
© 2006 Jones and Bartlett Publishers
Table 15.1. Distribution of height among British women
54*5+56*33+58*254+…
divided by 4995
=63.1 in. = mean height
€
∑ f ix i
N
€
x =
© 2006 Jones and Bartlett Publishers
Fig. 15.2. Graph of distribution of height among 4995 British women
mean=average
mean=
sum of all heightsdivided by
number of people
© 2006 Jones and Bartlett Publishers
Fig. 15.2. Graph of distribution of height among 4995 British women
mean = 63.1 inches
variance = 7.24 inches2
std dev = 2.69 inches
© 2006 Jones and Bartlett Publishers
Fig. 15.5. Features of a normal distribution
annotated bib.
36.3 = mean 2.4 = stdev
67%
95%99.7%
bell curve
© 2006 Jones and Bartlett Publishers
Fig. 15.4. Variance of a distribution measures the spread of the distribution around the mean
Variation in a trait
genetic
environmental
•genotypic variation•environmental variation•variation due to genotype-
by-environment interaction
•variation due to genotype-by-environment association
Variation in a trait
genotypic variation
the distribution of phenotypes, by itself, provides no information about how many genes influence a trait
due to differences in genotype
© 2006 Jones and Bartlett Publishers
Fig. 15.6. Segregation of independent genes affecting a quantitative trait
3 genes affect trait
A or a, B or b, C or c
each dominant contributes some to phenotype
© 2006 Jones and Bartlett Publishers
Fig. 15.7. Distribution of phenotypes determined by the segregation of 3 and 30 independent genes
3 vs 30 genes?
distribution is the same
Variation in a trait
genotypic variation
the distribution of phenotypes, by itself, provides no information about how many genes influence a trait
due to differences in genotype
© 2006 Jones and Bartlett Publishers
Fig. 15.8. Distribution of seed weight in a homozygous line of edible beans
inbred
beans
normalbell curve
© 2006 Jones and Bartlett Publishers
Fig. 15.8. Distribution of seed weight in a homozygous line of edible beans
Variation in a trait
environmental variation
due to differences in environment
the distribution provides no information about the relative importance of genotype or environment. Could be either/or or both
Variation in a trait
genetic and environmental variation
when both affect phenotype independently, the total variance is the sum of the individual variances
© 2006 Jones and Bartlett Publishers
Fig. 15.9. Combined effects of genotypic and environmental variance
Variation in a trait
genetic and environmental variation
when both affect phenotype independently, the total variance is the sum of the individual variances
totalvariance
genotypicvariance
environmentalvariance
= +
€
σ p2 =σ g
2 +σ e2
(eq. 15.3)
Variation in a trait
genetic and environmental variation
REVIEW:
•genotypic (G) variation•environmental (E) variation•variation due to G-E interaction•variation due to G-E association
variation due to G-E interaction
(genotype-by-environment)
corn poor environment
good environment
strain A does better than B
strain B does better than A
© 2006 Jones and Bartlett Publishers
Fig. 15.10. Genotype-by-environment interaction in maize. [Data from W. A. Russell. 1974. Annual Corn & Sorghum Research Conference 29: 81]
e.g.,
special varieties of plants developed to suit different growing areas
variation due to G-E (?) interaction
(genotype-by-sex)
sex different phenotype depending on gender of organism
living histogramand height
A homogeneous population…
…will have no genotypic variance.
€
σ p2 =σ g
2 +σ e2
€
σ g2 = 0
€
σ p2 =σ e
2Therefore:
© 2006 Jones and Bartlett Publishers
Fig. 15.6. Segregation of independent genes affecting a quantitative trait
cross
F1
cross
F2
inbred inbred
measureeye sizevariation
homogeneouspopulation
heterogeneouspopulation
F1
F2
€
σ 2 = 0.057 =σ e2
€
σ 2 = 0.563 =σ p2 =σ g
2 +σ e2
€
0.563−0.057 =σ g2 +σ e
2 −σ e2
€
0.506 =σ g2
broad-sense heritability H2
shows the importance of genetic variation, relative to environmental variation, in causing variation in phenotype
90% of eye variation in fish is genetic
ratio of genotypic variance to total phenotypic variance
€
H 2 =σ g2
σ p2=
σ g2
σ g2 +σ e
2=0.506
0.563= 0.90
© 2006 Jones and Bartlett Publishers
Fig. 15.13. Selection for increased length of corolla tube in tobacco
© 2006 Jones and Bartlett Publishers
Fig. 15.13. Selection for increased length of corolla tube in tobacco
M = mean of parental generation
M* = mean of selected parents
M’ = mean of progeny of selected parents
narrow-sense heritability
€
h2 =M ' −M
M* −M€
M ' −M( ) = h2 M* −M( )
narrow-sense heritability
ratio of additive genetic variance to the total phenotypic variance€
h2 =M ' −M
M* −M
broad-sense heritability H2
proportion of phenotypic variancedue to genetic differences
narrow-sense heritability h2
proportion of phenotypic variancedue to differences in additive alleles