SME
Evolutionary Biology · Problem type
Response to selection
Use this for “With h² = 0.4, breeders 2 cm taller than average give offspring how much taller?”
Chart
Selected: the top 76.6% of parents (above 76.37 cm), mean 82 cm: S = 2 cm.
R = h²S = 0.4 × 2 = 0.8 cm.
Offspring mean: 80 + 0.8 = 80.8 cm.
This is an example. Type your own values to start a new problem.
R (cm)
=
h²
×
S (cm)
μ
Mean before
example · cm
μ′
Mean after
calculated · cm
Formulas
R
=
h
2
×
S
0.8 = 0.4 × 2
μ
′
=
μ
+
R
80.8 = 80 + 0.8
Assumptions
•
h² is the narrow-sense heritability: the share of the variation passed on additively.
•
S is how far the chosen parents’ mean lies from the whole population’s mean.
•
The curves are drawn with a spread of 5 cm; R = h²S does not depend on it.
Step-by-step
WE KNOW
h² = 0.4, S = 2 cm, μ = 80 cm
FIND
response to selection (R), mean after (μ′)
Step 1 · Find response to selection (R)
Use R = h² × S
The
breeder’s
equation:
the
offspring
move
h
2
of
the
way
the
parents
were
chosen.
R
=
0.4
×
2
R
=
0.8
cm
Step 2 · Find mean after (μ′)
Use μ′ = μ + R
Move
the
old
mean
by
R
to
get
the
offspring’s
mean.
μ
′
=
80
+
0.8
μ
′
=
80.8
cm
Check
Put the numbers back in. Both sides should match.
0.8 = 0.4 × 2 ✓
80.8 = 80 + 0.8 ✓
Topic check
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