Synthetic theory of evolution. Peculiarities of action of evolutionary factors in human populations.

Lecturer : prof. Fefonyuk L.Ya.

Plan of lecture1. 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 speciesmacro-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 ViewsPre-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 possible to piece together a history of life on earth.

Adaptation to the environment is the interplay of random genetic variations and environmental conditions.

Synthetic (modern) Evolution Theory...             Darwinian evolution mixed with

modern genetic theoryMutations 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 timeThe 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  Hardy-Weinberg

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 NON-evolving 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,      p + q   =   1  

          HW equation...        (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-directionalGene Flow... migration of breeders... in/outGenetic 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 driftis 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 selectioncauses 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 selectionIn 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

F2 fitness Hybrid is fertile but F2 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.

Archaic Humans

Modern human

Diversification though

speciation

Diversification though behavioral changes

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

Chromosomal polymorphism have not regular nature, because it can leads to primary genetical isolation by failure of conjugation and crossing over.

Genetical polymorphism provide genetical originality of individual and human populations.

Medical importance of Genetical andChromosomal 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 Small races Small races

Ethnic groups(nations, nationality)

Ethnic groups(nations, nationality)

Ethnic groups(nations, nationality

Ethnic groups(nations, nationality)

Ethnic groups(nations, nationality)

Thank you for attention !

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