MECHANISMS OF CHANGE IN POPULATION (G8 GEN.BIO).pdf

Biology

1. MECHANISMS OFMECHANISMS OF
CHANGE INCHANGE IN
POPULATIONPOPULATION
GROUP 8
ZAIYANA PASINAG & AJ CHARISSE SHAYNE ATIBULA

2. Explain the
mechanisms that drive
changes in population,
including artificial
selection, natural
selection, genetic drift,
mutation, and
recombination.
Analyze how
environmental
and human
factors contribute
to changes in
species over time.
Apply the principles
of population
genetics to real-
world examples of
evolutionary
change.
OBJECTIVES:

3. For a population to start evolving, members of the population
should possess variations, which is the material on which agents
of evolution act. Any heritable trait is a characteristic of
organism that is influenced by the genes. Without any genetic
variation, the basic mechanism of evolutionary change cannot
activate.
WHAT ARE THE DIFFERENT MECHANISMS OF CHANGE IN
POPULATION?

4. - Occasionally, small alterations or changes
(mutations) occur during DNA replication.
- These mutations can be caused by various
factors, including:
Radiation
Viruses
Carcinogens (cancer-causing materials)
- The blueprint of any cell function is dictated
by its genotype.
MUTATION

5. EXAMPLE OF
MUTATION

6. GENE FLOW
Occurs when migrating individuals breed in a new location.
Immigrant genes can:
Add new alleles to the existing gene pool.
Modify allele frequencies if they come from a population
with different allele distributions.

7. Pollen or spores dispersed by
air to a new location.
Animals migrating due to
temperature changes.
Humans relocating to new
cities or countries.
Examples of gene flow events

8. - Occurs due to sexual reproduction,
introducing new gene combinations
into a population.
- A key source of genetic variation.
- Even siblings are not genetically
identical to their parents or each other.
- Happens during meiosis when
homologous chromosomes undergo
genetic recombination.
- Brings together new combinations of
genes
RECOMBINATION

9. - Refers to any change in allele
frequencies in a population due to
random sampling.
- In each new generation, some
individuals may leave behind more
descendants purely by chance.
- The genes passed on to the next
generation belong to these "luckier"
individuals, not necessarily the
healthiest or "better" ones.
GENETIC DRIFT

10. 2 TYPES OF GENETIC DRIFT

11. BOTTLENECK
EFFECT
When there is a noticeable decrease
in the size of a particular population
for at least one generation at the time.
CAUSES: Environmental disaster,
habitat destruction, and overhunting.
Random sampling of genes occurs.
The original population is impacted
the most.
GENETIC DRIFT:

13. FOUNDER'S
EFFECT
When a small number of "original"
individuals settle in a new region, the
new population may lack some alleles
found in the original population.
CAUSES: Migration of few individuals that
colonize a new area distant from the
original population.
Non-random sampling of genes occurs
The original population is not impacted
much or at all.
GENETIC DRIFT:

15. Charles Darwin’s theory of
natural selection states that
environmental changes often
favor different traits in a
species. As human activities
significantly alter the
environment, species adapt to
survive.
WHAT IS NATURAL
SELECTION?

16. A well-known example of this is
the Peppered Moth case, studied
by J.B.S. Haldane in 1924. The
moth exists in two color
variations: melanic (black) and
mottled (pale). In the 18th
century, pale moths were
dominant in Manchester’s
countryside.
WHAT IS N
SELECT
WHAT IS NATURAL
SELECTION?

17. However, during the Industrial
Revolution, tree trunks
darkened due to soot, making
pale moths more visible to
predators while black moths
became better camouflaged
and more likely to survive.
WHAT IS NATURAL
SELECTION?

19. WHAT IS NATURAL
SELECTION?
As a result, the melanic moths
became dominant. However, as
pollution levels decreased in the
20th century and trees returned to
their original color, the pale moths
once again replaced the melanic
ones. This case clearly
demonstrates the process of
natural selection in response to
environmental changes.

21. Artificial selection operates similarly to
natural selection but is guided by
human choices rather than natural
forces. While humans have
successfully altered allele frequencies
in dog breeds, no new species have
been created.
Biologically, a species is defined as a
population capable of interbreeding
and producing fertile offspring.
HOW DOES ARTIFICIAL
SELECTION WORKS?

22. HOW DOES ARTIFICIAL
SELECTION WORKS?
Since most dog breeds can interbreed
with each other and with wolves, they
are considered subspecies of the wolf
(Canis lupus).
Dog breeding exemplifies
microevolution, where allele
frequencies change within a
population but not to the extent of
forming a new species.

23. The Hardy-Weinberg Equilibrium states that if a certain
population has constant genetic stability, it is said to be at
equilibrium. This state is reached when allele and genotype
frequencies do not change from generation to generation.
In order to achieve such equilibrium, five important criteria
should be met:
(1) random mating;
(2) a very large population size;
(3) no migration between populations;
(4) no mutations; and
(5) no natural selection affecting the gene pool.
What happens when a population
will not undergo evolution?

24. If all the aforementioned criteria are met, two result will follow.
First, allele frequencies at a locus will stay constant from
generation to generation. After one generation of random
mating, the genotype frequencies will stay the same. Stating
the Second result in the form of an equation produces the:
THE HARDY-WEINBERG PRINCIPLE

25. A gene has two alleles, A and a
The frequency of allele A is represented by p
The frequency of allele a is represented by q
The frequency of genotype AA = p²
The frequency of genotype aa = q²
The frequency of genotype Aa = 2pq
p + q = 1
p² + 2pq + q²= 1
Hardy-Weinberg EQUATION:

26. The Hardy-Weinberg Equation is used to predict genotype
frequencies in a population and it is based on Mendelian
genetics. It is derived from a simple Punnett square in which p is
the frequency of the dominant allele and q is the frequency of
the recessive allele.

27. Assume a population in which 36% of the population
are homozygous for a certain recessive allele, a.
Assume the population is at equilibrium.
Question #1: What is the frequency of the recessive
allele, a in this population?
q² =0.36
q = √(0.36)
q = 0.6
EXAMPLE PROBLEM:

28. Assume a population in which 36% of the population
are homozygous for a certain recessive allele, a.
Assume the population is at equilibrium.
Question #2: What is the frequency of the dominant
allele, A in this population?
q = 0.6
p + 0.6 = 1
p = 0.4
EXAMPLE PROBLEM:

29. Assume a population in which 36% of the population
are homozygous for a certain recessive allele, a.
Assume the population is at equilibrium.
Question #3: What percentage of the population are
homozygous for the dominant allele, A?
p=0.40
p² = 0.40²
p² = 0.16=16%
EXAMPLE PROBLEM:

30. Assume a population in which 36% of the population
are homozygous for a certain recessive allele, a.
Assume the population is at equilibrium.
Question #4: What percentage of the population are
heterozygous for this trait?
2pq=2(0.40)(0.60)
2pq = 0.48=48%
EXAMPLE PROBLEM:

31. Assume a population in which 36% of the population
are homozygous for a certain recessive allele, a.
Assume the population is at equilibrium.
Question #5: Why do we have to start the problem with
the percentage of the homozygous recessive in the
population?
Answer: It is not possible to tell the homozygous
dominant (AA) from the heterozygous (Aa) by
examining the phenotype!
EXAMPLE PROBLEM:

32. The most important principle of the Hardy-Weinberg
equilibrium is that unless some agents acts to change
them, allele frequencies should not change to
generation to generation. More so, the equilibrium
shows the distribution of genotypes to be anticipated
for a population at genetic equilibrium at any value p
or q.

33. If the conditions set for the equilibrium to hold are not
found in nature, why is that necessary for such
equilibrium to be considered important? This is simply
because the Hardy-Weinberg equilibrium allows
biologists to determine whether evolutionary agents
are already operating together with the probable
agents (as evidence by the pattern of nonconformity
from the equilibrium).

34. THANK YOU