1) The document discusses factors that can initiate microevolutionary changes by altering gene frequencies in populations. These include mutation, gene flow, natural selection, non-random mating, and genetic drift. 2) Five conditions must be met for a population to maintain Hardy-Weinberg equilibrium: no mutation, random mating, no natural selection, large population size, and no gene flow. Deviations from any of these conditions can lead to evolutionary changes by changing allele and genotype frequencies over time. 3) Specific factors that can drive evolutionary changes include mutation, which introduces new variants; gene flow through migration; natural selection favoring certain genotypes; non-random mating patterns; and genetic drift through random processes in small populations

1. PRESENTATION TITLE
FACTORS INITIATING MICROEVOLUTIONARY CHANGES BY CHANGING
GENE FREQUENCIES
SUBJECT: EVOLUTION AND PRINCIPLES OF SYSTEMATIC ZOOLOGY
PRESENTED BY
AFTAB BADSHAH

2. Outline
 Evolution
 Microevolution
 Gene pool
 Gene frequency
 Hardy Weinburg theorem
 Factors initiating microevolutionary changes

3. What is evolution
Evolution, also known as descent with modification, is the change in
heritable phenotype traits of biological populations over
successive generations.
Scientifically evolution can be defined as “a change in the gene pool of a
population from generation to generation by processes like mutation,
natural selection, and genetic drift.”

4. microevolution
Microevolution is evolution on a small scale — within a single
population. That means narrowing our focus to one branch of the tree
of life.

6. What is gene pool
• Collection of all alleles of all genes possessed by members of a
population.
• Constitution of all copies of every type of allele at every locus in all
members of the population.

7. Gene frequency
• Proportion of a particular allele (variant of a gene) among all allele
copies being considered.
• Percentage of all alleles at a given locus in a population gene
pool represented by a particular allele
• The number of copies of a particular allele divided by the number of
copies of all alleles at the genetic place (locus) in a population.

8. Allele
frequency
Genotype
frequency

9. How Can We Check If A Population Is Evolving
The hereditary process alone does not produce evolutionary change. In
large bi-parental populations, allelic frequencies and genotypic ratios
attain an equilibrium in one generation and remain constant
thereafter unless disturbed by recurring mutations, natural selection,
migration, nonrandom mating, or genetic drift (random sorting). Such
disturbances are the sources of micro-evolutionary change.

10. HARDY-WEINBURG theorem
• The Hardy-Weinberg approach describes a hypothetical population
that is not evolving.
• But in real populations, the allele and genotype frequencies often do
change over time.
• The Hardy-Weinberg law is a logical consequence of Mendel’s first law
of segregation and expresses the tendency toward equilibrium
inherent in Mendelian heredity.
• Such changes can occur when at least one of the following five
conditions of Hardy-Weinberg equilibrium is absent:

11. 1. No mutations. The gene pool is modified if mutations alter alleles or if entire
genes are deleted or duplicated.
2. Random mating. If individuals tend to mate within a subset of the
population, such as their near neighbors or close relatives (inbreeding), random
mixing of gametes does not occur, and genotype frequencies change.
3. No natural selection. Differences in the survival and reproductive success of
individuals carrying different genotypes can alter allele frequencies.
4. Extremely large population size. The smaller the population, the more likely
it is that allele frequencies will fluctuate by chance from one generation to the
next (a process called genetic drift).
5. No gene flow. By moving alleles into or out of populations, gene flow can
alter allele frequencies.

12. Factors Initiating Evolutionary Changes
Any population which fails in Hardy-Weinberg equilibrium undergoes
evolutionary changes.
These evolutionary changes are brought about by the following
agencies which tend to alter the gene frequencies of the population

13. 1. Mutation.
• Mutations are changes in the structure of genes and chromosomes.
• Origin of all new genes and a source of variation that may prove
adaptive for an animal.
• The Hardy-Weinberg theorem assumes that no mutations occur or
that mutational equilibrium exists.
• Mutational equilibrium exists when a mutation from the wild-type
allele to a mutant form is balanced by mutation from the mutant back
to the wild type.

14. 2. Gene Flow
• Gene flow = migration either immigration or emigration
• The Hardy-Weinberg theorem assumes that no individuals enter a
population from the outside (immigrate) and that no individuals leave
a population (emigrate).
• Migration alters the gene frequency of the population by introducing
new alleles or escorts the population alleles to elsewhere.

15. 3. Natural Selection
• Natural selection= survival of the fittest
• Natural selection can change both allelic frequencies and genotypic
frequencies in a population.
• Natural selection acts on the whole animal, not on isolated traits.
• An organism that possesses a superior combination of traits will be
favored.
• Occurrence of natural selection in a population upsets the H-W
theorem

16. 4. Random Mating
• If mating is nonrandom, genotypic frequencies will deviate from
Hardy-Weinberg expectations.
• Individuals of the population mate independently not with the same
genotypes changes gene frequency
• Random mating upsets H-W theorem as the gene frequency changes.

17. 5. Genetic drift
• The changes in allele frequencies in a population due to random
fluctuations is simply termed as genetic drift.
• Genetic drift can lead to the loss or fixation of deleterious, neutral, or
beneficial alleles.
• Certain circumstances can result in genetic drift having a significant
impact on a population.
• Two examples are the founder effect and the bottleneck effect.

18. The Founder Effect
When a few individuals become isolated from a larger population, this
smaller group may establish a new population whose gene pool differs
from the source population; this is called the founder effect.
The Bottleneck Effect
A sudden change in the environment, such as a fire or flood, may
drastically reduce the size of a population. A severe drop in population
size can cause the bottleneck effect, so named because the population
has passed through a “bottleneck” that reduces its size

22. FURTHER READING.
1. Cell biology, molecular biology, genetics, evolution and ecology by P.S Verma and V.K Agarwal ;
multicolor edition; chapter 7; population genetics and evolution page 888----901.
2. Campbell biology 10th edition by Reece, Urry, Cain, Wasserman, Minorsky and Jackson; unit 4;
mechanisms of evolution; chapter 23 “the evolution of populations”; page 484----542.
3. Integrated principles of zoology 14th edition by Hickman, Roberts, Keen, Larson, I’Anson, Eisenhour; part
2, continuity and evolution of life; chapter 6, organic evolution; page 126---130.
4. Miller-Harley Zoology 5th edition; part 1, Biological principles; chapter 5, evolution and gene frequencies;
page 64---69.
5. Concepts of genetics by Robert J. Brooker, part VI, chapter 25; population genetics; page 614---640
6. Principles of genetics 6th edition by Snustad and Simmons; chapter 23; population genetics page 634---638.

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