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’}


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’}


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

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Offspring Population

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Female Parents

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aren

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{GYY, GYy, Gyy},{PY, Py}


Parent Population

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ametes:

Sperm + Eggs

Gametes are mixed by Ocean CurrentsFor pelagic spawners and broadcast spawners


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

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yG

ametes:

Sperm + Eggs

Gametes are mixed by Ocean CurrentsFor pelagic spawners and broadcast spawners


Parent Population

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YY

YY

YY

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YY

Yy

Yy

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Female Gametes

Mal

e G

amet

es



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.

mutation as an evolutionary force 1.it occurs when errors are made in duplicating alleles in...

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