Transcript 14. Synthetic theory of evolution

Synthetic theory of evolution.
Peculiarities of action of evolutionary
factors in human populations.
Lecturer : prof. Fefonyuk L.Ya.
Plan of lecture
1. Darwin theory of evolution
2. Synthetic theory of evolution
3. Agents of evolutionary change: mutation,
isolation, genetic drift (random fluctuation in
allele frequencies over time), gene flow, natural
selection.
4. Macroevolution. Microevolution .
4. Human population structure.
5. The evolution of human beings.
EVOLUTION...
progressive changes in organisms
that persist over time
helps explain the great
diversity, wide geographical
distribution, adaptations and
origins of organisms
EVOLUTION...
micro-evolution- changes in allele
frequency within a species
macro-evolution- new species, new
forms replacing old as revealed in the
fossil record
Darwinian (classical) Evolution
Theory (24 Nov 1859)
is based upon theory of Natural
Selection
Origin of Species
only small fraction of progeny of a
generation survive
survivors have traits (alleles) promote
their survival depends on all genes acting
together
Darwinian Natural Selection
is defined as :
is a change in allele frequency
from generation to generation,
as influenced by environment
that promotes progeny
survival.
"Survival of Fittest "
Contrast of World Views
Pre-Darwinian View
Post-Darwinian View
Earth is relatively young-age is
measured in thousands of years
Earth is relatively old – age is
measured in billions of years
Each species is specially created;
species don’t change, and the
number of species remains the
same.
Species are related by descent – it is
possible to piece together a history
of life on earth.
Species are related by descent – it is Adaptation to the environment is
possible to piece together a history the interplay of random genetic
of life on earth.
variations and environmental
conditions.
Synthetic (modern) Evolution Theory...
Darwinian evolution mixed with
modern genetic theory
Mutations are the raw material for
evolutionary change
Population - elementary unit of evolution
(Population – any group of individuals, usually of
a single species, occupying a particular area at
the same time
The elementary factors of evolution that
changes genetic structure of a population are:
mutation, isolation, genetic drift, gene flow,
and natural selection.
EVOLUTION
Change in gene pool ....... leads to
better fitness ....... which leads to
adaptation ....... which leads to
reproductive success
Evolution - better adapted genes
leaving more progeny
population genetics HardyWeinberg Equilibrium
1908 G.H.Hardy, English
mathematician & G.Weinberg, German
physician
Law of Genetic Equilibrium
describes the gene pool (i.e., all the
alleles present) mathematically
defines the ideal case of a NONevolving populations
Hardy-Weinberg Equilibrium
for an ideal case... a number of criteria
must be met...
must be an infinitely large populations
(large sample sizes)
should exhibit random mating
absence of forces which can change allele
frequencies
-no migration (in/out)
-no mutation
- no selection
-each allele is equally viable (no
lethals)
Hardy-Weinberg Equilibrium
HW law states -->
original percentage of a genotypes alleles
remains constant
HW can be defined algebraically, by the binomial expansion
any gene with 2 allelic forms....
A and a
let frequency of one allele
(A) =
p
& frequency of other allele
(a) =
q
then by definition,
HW equation...
p+q = 1
(p + q)2 = p2 + 2pq + q2 = 1
GG
Gg
gg
Agents of evolution.
But..... Allele frequencies do change over time
via....
Mutation... 1/10,000, random, non-directional
Gene Flow... migration of breeders... in/out
Genetic Drift... random loss of alleles - due to
failed matings in very small populations, it's a
statistical anomaly
can lead to fixation or
deletion of alleles
Mutation the row material for
evolutionary change.
a permanent change in a gene, such as an
alteration of its nucleotide sequence.
Mutations provide new alleles, and therefore
they underlie all the other mechanisms that
provide variation.
In a changing environment, however, even a
seemingly harmful mutation can be a source
of variation that can help a population
become adapted to a new environment.
Gene flow (gene migration )
is the movement of alleles between
populations by (the migration of breeding
individuals)
Gene flow can increase the variation
within a population by introducing novel
alleles that were produced by mutation in
some other population.
Continued gene flow between populations
makes their gene pools similar and reduces
the possibility of allele frequency
differences between populations that
might be due to natural selection and
genetic drift.
Nonrandom mating and
Assortative mating
Nonrandom mating occurs when individuals
pair up by chance and not according to
their genotypes or phenotypes.
In human population, inbreeding increases
the frequency of recessive abnormalities.
Assortative mating occurs when individuals
tend to mate with those that have the
same phenotype with respect to some
characteristic (in humans tall women seem
to prefer to mate with tall men).
Genetic drift
is a random fluctuation in allele frequencies
over time.
Genetic drift occurs in both large and small
populations, a larger population is expected
to suffer less of a sampling error than a
smaller population.
When population is small, there is greater
chance that some rare genotype might not
participate at all in the production of the
next generation.
Genetic drift
The founder effect
is an example of genetic drift in which rare
alleles, or combinations of alleles, occur at a
higher frequency in a population isolated from
the general population.
After all, founding individuals contain only a
fraction of the total genetic diversity of the
original gene pool. Which particular alleles are
carried by the founders is dictated by chance
alone.
Founder's Principle... little dispersal - new allele
predominates - small human tribes
Bottleneck Effect
Sometimes a population is
subjected to near extinction
because of a natural disaster
(earthquake or fire) or because
of slaughter by humans.
Bottleneck Effect... natural disasters
leave survivors which are not representative
of whole population
Natural selection
causes the allele frequencies of a
gene pool to change (total variety of
genes and alleles present in a sexually
reproducing population, in any given
population the composition of the
gene pool may constantly changes
from generation to generation, and
when it does the members of a
population become more adapted to
their environment.)
Natural selection- acts on
individuals of populations
Types of Selection
STABILIZING - limits extremes of
population one optimum phenotype - ex: human
birth weight
DIRECTIONAL- one best phenotype, not the
mean gradual replacement one by another
DIVERSIFYING (disruptive)- increases the
fitness of extremes no optimum phenotype (2 or
more) - patchy environments ex: sexual
dimorphism
Types of Selection
Selection...
better fit individuals are better
reproducers
Artificial - animal husbandry selects
best - mustards-
Natural selection
In the context of population genetics
evolution by natural selection requires the
following steps:
Variation. The members of population differ
from one another.
Inheritance. Many of these differences are
inheritable, genetic differences.
Differential reproduction. Because of these
differences, some phenotypes are more fit and
reproduce to a greater extent than the other
members.
Accumulation of adaptive traits. With each
generation, alleles contributing to reproductive
success increase in frequency.
Microevolution
– a change of gene frequency in a
population which can finish formation of
new species.
Species – a group of organisms
constituting a single gene pool; its
members can breed with each other but
not with organisms of another species
(species are reproductively isolated from
one another).
Some Evolutionary barriers to forming hybrids which
can lead to REPRODUCTIVE ISOLATION
Isolating Mechanism
Example
PREMATING (prezygotic)
Habitat
Species at same locale occupy different habitats
Temporal
Species reproduce at different seasons or different times
of day
Behavioral
In animals, courtship behaviour differs or they respond
to different songs, calls, pheromones, or other signals
Mechanical
Genitalia unsuitable for one another
POSTMATING (postzygotic)
Gamete isolation
Sperm cannot reach or fertilize egg
Zygote mortality
Hybrid dies before maturity
Hybrid sterility
Hybrid survives but is sterile and cannot reproduce
F fitness
Hybrid is fertile but F hybrid has lower fitness.
Macroevolution –
Macroevolution – is the study of
evolutionary change above the
species level – genus, family, order,
class, and phylum.
Main stages evolution of Human
beings
The Early Hominids.
Diversification though
speciation
Archaic Humans
Diversification though
behavioral changes
Modern human
Diversification though
cultural changes
evolution of Human beings
Homo sapiens survived as a result of erect bipedal
posture,
increased manual dexterity,
feet suited for walking and running,
and better developed creative brains.
Human and chimpanzee?!!
Human karyotype have 23, а — chimpanzee
karyotype -24 chromosomal pars :
second human chromosome — it is two separate
chimpanzee chromosomes;
13 chromosome pairs identical;
9 pairs differ by the centromere localization
( perycentromere parts are inverted)
99 % genes similarity of human and chimpanzee
Human and chimpanzee? ! !
The main result biological evolution –
speciation in human society is not
realized, but influence of main
evolution factors leads to genetical
variety, occur on intraspecific
intrapopulation level by the
microevolution processes.
Polymorphism
Ecologycal
(adaptational)
genetical
polymorphism –
selection individuals
that genetically better
adapted to the
environment
Balanced
(heterozygous)
genetical
polymorphism) –
promote reservation
recessive alleles by
superdominance.
Example: Sickle-Cell disease
Genetical
polymorphism
provide
genetical
originality of
individual and
human
populations.
Chromosomal
polymorphism
have not regular
nature, because it
can leads to
primary genetical
isolation by failure
of conjugation and
crossing over.
Medical importance of Genetical and
Chromosomal polymorphism
Adaptive human types
That factors maintenance individual
morphological diversity and interspecies
division mankind into adaptive human
types, constitutive groups and races.
Humans often categorize themselves in
terms of race or ethnicity.
Genetic studies have demonstrated that
humans on the African continent are most
genetically diverse (Y-chromosome and
MtDNA and lineages).
The majority of genetic variation occurs
within "racial groups", with only 5 to 15%
of total variation occurring between racial
groups.
Races
Human racial categories are
based on both ancestry and
visible traits, especially skin
color and facial features.
It has been also claimed that
"the greatest genetic structure
that exists in the human
population occurs at the racial
level"
Large races
Small races
Ethnic groups
(nations, nationality)
Small races
Small races
Ethnic groups
(nations, nationality)
Ethnic groups
Ethnic groups(nations, nationality))
Ethnic groups
(nations, nationality)
(nations, nationality))
Thank you for attention !
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