Mutation as an Evolutionary Force 1.It occurs when errors are made in duplicating alleles in...
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Transcript of Mutation as an Evolutionary Force 1.It occurs when errors are made in duplicating alleles in...
Mutation as an Evolutionary Force
1. It occurs when errors are made in duplicating alleles in producing the gametes.
2. It is one of the weaker evolutionary forces, because errors are relatively rare. The error rate or mutation rate, , in copying an allele of a nuclear gene is ~ 1 x 10-6 to 1 x 10-9.
3. It changes allele frequencies in a population and this change in the genetic composition of a population from parents to offspring is what we mean by evolution.
No Mutation
AA Parents produce only ‘A’ bearing gametes.
Aa Parents produce ½ ‘A’ and ½ ‘a’ bearing gametes
aa Parents produce only all ‘a’ bearing gametes.
With Mutation
AA Parents produce some ‘a’ bearing mutant gametes.
Aa Parents produce ½ ‘A’ and ½ ‘a’ gametes
aa Parent produce some ‘A’ bearing mutant gametes.
Offspringpopulation
= A alleles
= a alleles
Parentpopulation
ReproductionWith Mutation
How strong is mutation as an evolutionary force?
Calculate how much the frequency of an allele changes in the population as a result
of mutation.
A aμMechanism of
MutationAllele in the
Parent
Mutant Allele in the Gamete and then
In the Offspring
Aa
Allele in the Parent
Mutant Allele in the Gamete and then
In the Offspring
Change in allele frequency, Pa, as a result of mutation
A aμMechanism of
Mutation
Parent Frequencies:{PA, Pa}
Offspring Frequencies:{PA’, Pa’}
ReproductionWith Mutation
How similar are PA’ and PA?
Pa’ = (1- v) Pa + μPA
The change in allele frequency, Pa, caused by mutation
Freq of a allele in offspring
after mutation
Non-Mutation rate times the
Freq of a before mutation
Mutation rate from A to a times
the Freq of A before mutation
ΔPa = Pa’– Pa = μ – ( + )Pa
Parent Frequencies:{PA, Pa}
Offspring Frequencies:{PA’, Pa’}
ReproductionWith Mutation
An Evolutionary Equilibrium occurs when P = 0
• Evolution: change in allele frequency in a population from one generation to the next.
P > 0 the allele is increasing in frequencyP < 0 the allele is decreasing in frequency• No Evolution: No change in allele frequency in a
population from one generation to the next. P = 0 the allele is neither increasing nor
decreasing in frequency• The Equilibrium Allele Frequency, P*, is the
frequency that makes P = 0
Set ΔPa = 0 = μ – ( + )Pa*Solve for Pa*
The change in allele frequency, Pa, caused by mutation
ΔPa = Pa’– Pa = μ – ( + )Pa
What is the Equilibrium Allele Frequency, Pa*?
The Equilibrium Allele Frequency,Pa*, that makes Pa = 0
At the Mutation Equilibrium, ΔPa = 0.
0 = μ – ( + )Pa*
P*a = μ/( + )
The Equilibrium Allele Frequency =Rate at which A is wrongly copied as a,
Relative to all errors of copying at this gene.
Parent Population
YY
YY
YY
YY
YY
YY
Yy
Yy
YyYy
Yy
Yy
yyyy
yy
yy
yyyyyy
Offspring Population
YY
YY
YY
YY
YY
YY
YyYy
YyYy
Yy
Yy
yyyy
yy
yy
yyyyyy
YY Yy yy
YY
OffspringYy
yy
Female Parents
Mal
e P
aren
ts
{GYY, GYy, Gyy},{PY, Py}
{GYY, GYy, Gyy},{PY, Py}
Parent Population
YY
YY
YY
YY
YY
YY
Yy
Yy
YyYy
Yy
Yy
yyyy
yy
yy
yyyyyy
Offspring Population
YY
YY
YY
YY
YY
YY
YyYy
YyYy
Yy
Yy
yyyy
yy
yy
yyyyyy
{GYY, GYy, Gyy},{PY, Py}
Y
Y
Y
Y
Y
YY
Y
Y
YY
Y
YY
yy
y
yy
y yyy
yy
yy
yy
yy
yy
yy
yG
ametes:
Sperm + Eggs
Gametes are mixed by Ocean CurrentsFor pelagic spawners and broadcast spawners
{GYY, GYy, Gyy},{PY, Py}
Pelagic eggs - eggs that float in the water column, like most deep water marine fishes and coral reef fishes.Pelagic Scatterers – spawn by scattering eggs and sperm into the water in schools near surface. For example:sardines, mackerel, tuna, whitefish.Broadcast Spawners: another name for forming zygotes by scattering eggs and sperm into the water
Examples: Thunnus thynnus, atlantic blue fin tuna 10 feet long, weigh up to 1,400 pounds, lifespan longer than 20 years. the largest bony fish in the world; they migrate up to 5,000 miles.
0.8 to 2.6 million eggs per spawning female (roughly 100,000 eggs/kg).Eggs are ~ 1 mm in diameter and buoyant, enclosed in an oil droplet.LABRIDAE (WRASSES) All species are proto-gynous hermaphrodites: Females have the capacity to turn into males. Males are either born as males or are older sex-reversed females. Star Fishes.
Parent Population
YY
YY
YY
YY
YY
YY
Yy
Yy
YyYy
Yy
Yy
yyyy
yy
yy
yyyyyy
Offspring Population
YY
YY
YY
YY
YY
YY
YyYy
YyYy
Yy
Yy
yyyy
yy
yy
yyyyyy
{GYY, GYy, Gyy},{PY, Py}
Y
Y
Y
Y
Y
YY
Y
Y
YY
Y
YY
yy
y
yy
y yyy
yy
yy
yy
yy
yy
yy
yG
ametes:
Sperm + Eggs
Gametes are mixed by Ocean CurrentsFor pelagic spawners and broadcast spawners
{GYY, GYy, Gyy},{PY, Py}
Parent Population
YY
YY
YY
YY
YY
YY
Yy
Yy
YyYy
Yy
Yy
yyyy
yy
yy
yyyyyy
Offspring Population
YY
YY
YY
YY
YY
YY
YyYy
YyYy
Yy
Yy
yyyy
yy
yy
yyyyyy
Female Gametes
Mal
e G
amet
es
{GYY, GYy, Gyy},{PY, Py}
{GYY, GYy, Gyy},{PY, Py}
Y
PY
y
Py
Y PYYY
(PY)2
Yy
PYPy
y PyYy
PYPy
yy
(Py)2
Random Mating =Random Union of
Gametes
Human Blood Groups:
Number of Individuals: MM MN NN Total 1787 3037 1305 6,129Genotype Frequencies: 0.292 0.495 0.213 1.00
Number of Alleles: M N Total 6611 5647 12,258
Allele Frequencies: 0.539 0.461 1.00
Predicted Genotype (0.539)2 2(0.539)(0.461) (0.461)2
Frequencies from HWE 0.291 0.497 0.212
Actual Observed 0.292 0.495 0.213
Human Blood Groups are in Hardy-Weinberg Equilibrium
Predicted Genotype (0.539)2 2(0.539)(0.461) (0.461)2
Frequencies from HWE 0.291 0.497 0.212Actual Observed 0.292 0.495 0.213
Conclude: Humans are mating at random with respect toblood groups!
Conclude: No evidence of natural selection or any otherevolutionary forces acting on these alleles.
Conclude: We are mating like pelagic spawners as far asthis gene is concerned!
Conclude: Nonrandom mating can be occurring for sometraits and genes but not others in the samepopulation.