Population genetics
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Population Genetics. Population Genetics:. The study of allele frequencies within a population. Changes in allele frequencies are caused by the following: Natural Selection Genetic Drift Mutation Gene Flow. Natural Selection.

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Population Genetics

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Population genetics

Population Genetics


Population genetics1

Population Genetics:

  • The study of allele frequencies within a population.

  • Changes in allele frequencies are caused by the following:

    • Natural Selection

    • Genetic Drift

    • Mutation

    • Gene Flow


Natural selection

Natural Selection

A process whereby creatures with good traits survive and reproduce and where creatures with negative traits, die off.


Genetic drift

Genetic Drift

  • Changes in allele frequencies due to the fact that alleles in offspring are a random sample of those in parents.

  • Not a result of which traits are beneficial, genetic drift is random.


Causes of mutation

Causes of Mutation

Spontaneous

Radiation

Chemicals/pollution

Crossing over during meiosis

Meiosis makes sperm and egg


Gene flow

Gene Flow

  • Transfer of alleles from one population to another.

  • Caused by the migration of organisms


Genetics

Genetics

  • Let’s say “B” = Brown and “bb” = white.

  • Geneticists can predict babies

  • Bb x bb = 50% Brown and 50% White


Genetics1

Genetics

  • Let’s say “B” = Brown and “bb” = white.

  • Let’s say that 4% of a population is white.

  • Geneticists can now predict for the population

4% = 0.04

“bb”= 0.04

“b” x “b” = 0.04

The square root of 0.04 = 0.2

“b” = 0.2

Therefore “b” = 20% of all alleles

B

b

= 0.2

4% of the population

B

BB

Bb

4%

b

= 0.2

bB

bb


Genetics2

Genetics

  • If “b” = 20% of all alleles, then…

  • “B” must equal 80%.

B = 0.8

b = 0.2

4% of the population

B = 0.8

BB

Bb

4%

b = 0.2

bB

bb


Population genetics

What percent of the bunny population will be homozygous dominant?

B = 0.8

b = 0.2

64%

16%

B = 0.8

BB

Bb

16%

4%

b = 0.2

4% of the population

bB

bb

64% will be BB.

32% will be hybrids


Population genetics

A new recessive mutation has resulted in 9% of the USA becoming vampires. What percent of the population will be carriers?

N = 0.7

n = 0.3

49%

21%

N = 0.7

21%

9%

n = 0.3

42% will be carriers.


Population genetics

“b” = 0.6. Do the rest.

B = 0.4

b = 0.6

16%

24%

B = 0.4

24%

36%

b = 0.6

What are the percentages of the different genotypes? Fill out the punnett.


Population genetics

No mutation: no allelic changes occur.

No gene flow: Animals do not enter or leave the population.

Random mating: individuals pair by chance and not according to the genotypes or phenotypes.

Large population: the population is large so changes in allele frequencies due to chance are insignificant. Large populations decrease chances of genetic drift.

No selection: All genotypes are healthy and there is no selective force that favors one genotype over another.


Population genetics

Within a population of moths, the color dark (D) is dominant over the color white (d). Before the industrial revolution, nearly 81% of all moths were white. What percentage of the population was DD before the environment was polluted?

D = 0.1

d = 0.9

1%

9%

D = 0.1

dd

9%

81%

D _

d = 0.9

1% of the butterflies will be DD.


Population genetics

Mutations occur

Gene Flow. Animals enter or leave the population, thereby introducing or eliminating alleles.

Non-random mating. Animals breed according to phenotypes or genotypes.

Small population

Selection. One genotype is selected over another.

Which moth was selected for during the industrial revolution?


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