Understanding Population Genetics and Allele Frequency Changes

 
Population Genetics
 
Life Science
Mannix 2018-2019
 
Introduction
 
Population genetics is the study of change in
the frequencies of alleles within a population.
1 allele comes from mom and the other from dad.
2 alleles together is called the genotype
The physical representation of the genotype is the
phenotype.
 
5 Factors that change Allele Frequency
 
1.
Mutation rates
2.
Migration in and out of an area
3.
Genetic drift
4.
Nonrandom mating
5.
Natural selection
 
Mutations
 
Errors in DNA or RNA replication
Causes new variations!
Remember only variations that help out an
organism (make them better suited to survive will
continue to show up over and over again through
the generations)
 
https://www.youtube.com/watch?v=GieZ3pk9Y
Vo
 
 
Migration
 
Movement of individuals from one population to
another.
Immigration: movement into a population
Ex: A flock of birds move into a new area for a certain season
Ex: Humans move to a country that is NOT where they are
born.
Emigration: movement out of a population
Ex: When the flock of birds left their original living place.
Ex: Human leave the place they were born.
 
A huge influence to changes in allele frequencies.
 
Genetic Drift
 
RANDOM loss of alleles in a certain area.
Founder Effect: small group of individuals move
away
Bottleneck Effect: a sudden decrease in
population size due to some kind of natural
disaster.
 
https://www.youtube.com/watch?v=W0TM4LQm
oZY
 
Genetic Drift Examples
 
Does the below example represent the Founders
effect or the Bottleneck effect? How do you know?
 
Afrikaner population of Dutch settlers in South
Africa is descended mainly from a few colonists.
Today, the Afrikaner population has an unusually
high frequency of the gene that causes
Huntington's disease, because those original
Dutch colonists just happened to carry that gene
with unusually high frequency.
 
Genetic Drift Examples
 
Does the below example represent the Founders
effect or the Bottleneck effect? How do you know?
 
Northern elephant seals have reduced genetic
variation probably because of a population
bottleneck humans inflicted on them in the
1890s. Hunting reduced their population size to
as few as 20 individuals at the end of the 19th
century
 
Nonrandom Mating
 
Mating that occurs more or less frequently
than expected (does not fit a regular punnett
square)
Inbreeding: mating with relatives, increases
homozygous recessive traits.
Out breeding: mating with non-relatives, increase
heterozygosity. (MORE DIVERSE/BETTER!!)
 
Selection
 
Artificial Selection:
People influenced
We select traits for a desired outcome.
 
EX: Labardoodle or Pomchi
 
Selection
 
Natural Selection: the environment selects for
the traits that are best FIT to survive.
 
https://thekidshouldseethis.com/post/evoluti
on-101-how-natural-selection-works-nova-pbs
 
Types of Natural Selection
 
Stabilizing
Extreme phenotypes are eliminated in a
population.
Disruptive
Intermediate (middle) phenotypes are eliminated
in a population.
Directional
A single extreme phenotype is eliminated in a
population.
 
Stabilizing Selection
 
Favors the average individuals!
 
 
Stablilizing Selection
 
 
Disruptive Selection
 
Extreme traits are preferred
 
In the African seed-cracker finch, large and small
beaked birds are more common because they
are able to open the large and small seeds
present in the population.
 
Disruptive Selection
 
 
Directional Selection
 
One particular phenotype is favored.
 
 
Fossil records show that black bears in Europe
decreased in size during periods between
continental glacial coverage during the ice ages, but
increased in size during the glacial period. This was
likely because larger individual enjoyed an
advantage in conditions of limited food supplies
and extreme cold.
 
Directional Selection
 
 
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Population genetics explores how allele frequencies change within populations due to factors like mutations, migration, genetic drift, nonrandom mating, and natural selection. Mutations introduce new variations, migration affects gene flow, genetic drift causes random allele loss, and examples like founder and bottleneck effects illustrate genetic changes over time.


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  1. Population Genetics Life Science Mannix 2018-2019

  2. Introduction Population genetics is the study of change in the frequencies of alleles within a population. 1 allele comes from mom and the other from dad. 2 alleles together is called the genotype The physical representation of the genotype is the phenotype.

  3. 5 Factors that change Allele Frequency 1. Mutation rates 2. Migration in and out of an area 3. Genetic drift 4. Nonrandom mating 5. Natural selection

  4. Mutations Errors in DNA or RNA replication Causes new variations! Remember only variations that help out an organism (make them better suited to survive will continue to show up over and over again through the generations) https://www.youtube.com/watch?v=GieZ3pk9Y Vo

  5. Migration Movement of individuals from one population to another. Immigration: movement into a population Ex: A flock of birds move into a new area for a certain season Ex: Humans move to a country that is NOT where they are born. Emigration: movement out of a population Ex: When the flock of birds left their original living place. Ex: Human leave the place they were born. A huge influence to changes in allele frequencies.

  6. Genetic Drift RANDOM loss of alleles in a certain area. Founder Effect: small group of individuals move away Bottleneck Effect: a sudden decrease in population size due to some kind of natural disaster. https://www.youtube.com/watch?v=W0TM4LQm oZY

  7. Genetic Drift Examples Does the below example represent the Founders effect or the Bottleneck effect? How do you know? Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington's disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency.

  8. Genetic Drift Examples Does the below example represent the Founders effect or the Bottleneck effect? How do you know? Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century

  9. Nonrandom Mating Mating that occurs more or less frequently than expected (does not fit a regular punnett square) Inbreeding: mating with relatives, increases homozygous recessive traits. Out breeding: mating with non-relatives, increase heterozygosity. (MORE DIVERSE/BETTER!!)

  10. Selection Artificial Selection: People influenced We select traits for a desired outcome. EX: Labardoodle or Pomchi

  11. Selection Natural Selection: the environment selects for the traits that are best FIT to survive. https://thekidshouldseethis.com/post/evoluti on-101-how-natural-selection-works-nova-pbs

  12. Types of Natural Selection Stabilizing Extreme phenotypes are eliminated in a population. Disruptive Intermediate (middle) phenotypes are eliminated in a population. Directional A single extreme phenotype is eliminated in a population.

  13. Stabilizing Selection Favors the average individuals!

  14. Stablilizing Selection

  15. Disruptive Selection Extreme traits are preferred In the African seed-cracker finch, large and small beaked birds are more common because they are able to open the large and small seeds present in the population.

  16. Disruptive Selection

  17. Directional Selection One particular phenotype is favored. Fossil records show that black bears in Europe decreased in size during periods between continental glacial coverage during the ice ages, but increased in size during the glacial period. This was likely because larger individual enjoyed an advantage in conditions of limited food supplies and extreme cold.

  18. Directional Selection

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