The document discusses Hardy-Weinberg equilibrium, which explains that allele and genotype frequencies remain constant from generation to generation in a population without evolutionary influences. It will remain constant in an infinitely large random breeding population without factors like selection, migration, or mutation. The document then discusses the conditions required for Hardy-Weinberg equilibrium and various agents that can cause evolutionary change like mutation, gene flow, non-random mating, genetic drift, and natural selection.

1. Hardy-Weinberg equilibrium
By
Dr. Amreen Ahmad

2. Hardy-Weinberg equilibrium
The Hardy–Weinberg principle, also known as
the Hardy–Weinberg equilibrium, model,
theorem, or law explains that allele and
genotype frequencies in a population will
remain constant from generation to generation
in the absence of other evolutionary influences.

4. • The law was proposed by a British
mathematician Hardy and a German physician
Weinberg (1908) independently.
• It states that both gene frequencies and
genotype frequencies will remain constant
from generation to generation in an infinitely
large interbreeding population in which
mating is at random and no selection,
migration or mutation occurs.

5. Hardy-Weinberg theorem
• Counting Alleles
– assume 2 alleles = B, b
– frequency of dominant allele (B) = p
– frequency of recessive allele (b) = q
• frequencies must add to 1 (100%), so:
p + q = 1
BB Bb bb

7. Conditions of the Hardy-Weinberg
population are
• Random mating
• No mutation
• No natural selection
• No gene flow or migration
• A very large population size (no genetic drift)

8. Agents of evolutionary change
Mutation Gene Flow Non-random mating
Genetic Drift Selection

9. Mutation
• Changes in the genetic material.
• Mutations are random (indiscriminate) and
occur in all directions.

10. Gene flow
• Gene flow refer to the movement of alleles
from one population to another as a result of
interbreeding between members of the two
population
• Removal of alleles from one population or
addition of alleles into another population

11. Non-random mating
Organisms may prefer to mate with others of the same
genotype or of different genotypes. Non-random mating
won't make allele frequencies in the population change by
itself, though it can alter genotype frequencies. This keeps
the population from being in Hardy-Weinberg equilibrium

12. Genetic drift
Genetic drift involves changes in allele
frequency due to chance events – literally,
"sampling error" in selecting alleles for the next
generation. Drift can occur in any population of
non-infinite size, but it has a stronger effect on
small populations

13. • Genetic drift can also operate through founder
effect. In this, genetic drift can cause dramatic
changes in the allele frequencies in a
population derived from small groups of
colonisers, called founders, to a new habitat.
• These founders do not have all of the alleles
found in their source population. These
founders become quickly different from the
parental population and may form a new
species, e.g. evolution of Darwin finches on
Galapagos Islands which were probably
derived from a few initial founders.

14. Population bottleneck
• It is reduction in allele frequencies caused by
drastic reduction in population size called
population crash e.g. decrease in cheetah
population in Africa due to over-hunting.
• As the given gene pool is limited, population
bottleneck often prevents the species to re
establish its former richness so new population
has a much restricted gene pool than the larger
parent population.

15. • Genetic drift can have major effects when a
population is sharply reduced in size by a
natural disaster (bottleneck effect) or when a
small group splits off from the main
population to found a colony (founder effect)

16. Natural selection
• Natural selection occurs when one allele (or
combination of alleles of different genes)
makes an organism more or less fit, that is,
able to survive and reproduce in a given
environment. If an allele reduces fitness, its
frequency will tend to drop from one
generation to the next