Genetic diversity: the hidden face of biodiversity What is genetic diversity? Genetic diversity is the genetic variation within and between populations

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Genetic diversity: the hidden face of biodiversity

What is genetic diversity?• Genetic diversity is the genetic variation within and between populations of organisms.• Genetic diversity is the foundation for all higher levels of biodiversity (species and population diversity, and in turn community and ecosystem diversity).

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Genetic diversity

Nature of genetic diversity• Information of life are stored in DNA of living organisms (book of life).

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Genetic diversity

Nature of genetic diversity• DNA when complexed with proteins is called chromatin.• Chromatin condenses during cell division to form a chromosome.

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Genetic diversity

Nature of genetic diversity• A section of DNA along the chromosome that codes for (contains the information) a single polypeptide chain to make a protein is a gene.

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1. The four letters All genetic code is spelled out

with just four chemical letters, or bases: adenine (A), thymine (T), cytosine (C) and guanine (G). These pair up, A with T and G with C. The human genome has between 2.8 and 3.5 billion base pairs.

Genetic diversityNature of genetic diversity

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2. DNA double helix The base pairs form the rungs

of the ladder-like DNA double helix. The length of DNA is the long sequences of bases which are the code for life.


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3. Genes Genes are special sequences of

hundreds or thousands of base pairs that provide the templates (RNAs) for all proteins to be produced.

They are sections of DNA that are responsible for the development of characteristics.

Genes occupy positions on the chromosomes called loci.


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4. Chromosomes DNA is tightly packaged

(coiled) into thread-like structures called chromosomes.

Every human has 23 pairs of chromosomes, one set from each parent.


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5. Nucleus and cell The 46 chromosomes are

located in the nucleus of cells, except in germ cells, where 23 chromosomes are present.


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6. Body The body is built from trillions

of variety of cells (blood, muscle, nerve, bone, etc….).


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Genetic diversity

Nature of genetic diversity• A given gene may have more than one form.• The alternative (different) forms of a single gene are called alleles.

flower colorgene withtwo alleles

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Genetic diversity

Nature of genetic diversity• Homozygous individuals:

• are individuals with two similar alleles for one gene• Heterozygous individuals:

• are individuals with two different alleles for one gene.

Homozygous(both alleles in an individual are the same)

Heterozygous(two different alleles present in an individualfor one gene)

or flower colorgene

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Genetic diversity

Origin of genetic diversityHow does genetic variation arise?.1. Mutation• The ultimate source of genetic variation in populations is via

mutation. • There are two general types of mutations:

a. point mutation: is a change in one nucleotide or a few nucleotides in a single gene through:

base pair substitutions.

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Genetic diversity

Origin of genetic diversityHow does genetic variation arise?.1. Mutation

a. point mutation: is a change in one nucleotide or a few nucleotides in a single gene through: base pair insertions (additions) or deletions (losses).

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Genetic diversity


b. chromosomal mutation through: change in chromosome structure (change in the number

and arrangement of genes in a chromosome).

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Genetic diversity


b. chromosomal mutation through: change in chromosome number (change in the number

of individual chromosomes or in the number of the complete set of chromosomes).

2n 2n 2n

321 421 321

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Genetic diversity


b. chromosomal mutation through: change in chromosome number (change in the number

of individual chromosomes or in the number of the complete set of chromosomes).

2n 3n 4n

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Genetic diversityOrigin of genetic diversityHow does genetic variation arise?.2. Meiosis and fertilization

• Behavior of chromosomes during meiosis and fertilization are responsible for most of genetic variation.

• Three mechanisms contribute to genetic variation: independent assortment of chromosomes: random

orientation of homologous chromosomes during meiosis in metaphase and anaphase contributes to genetic variation.

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independent assortment of chromosomes

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Crossing over: in prophase I, homologous chromosomes exchanges their genes. This genetic recombination caused by crossing over produces recombinant chromosomes (chromosomes with recombined genes derived from both parents).

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Random fertilization: any sperm can fuse with any egg. A zygote produced by fertilization has a unique genetic identity.

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Genetic diversityEvolutionary processesWhat is evolution?• Evolution is the changes in allele frequencies within a population.• Evolution is a change in the genetic makeup (composition) of populations over generations.

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Genetic diversity

Evolutionary processesWhat causes evolution?1. Mutation.2. Natural selection.3. Gene flow.4. Genetic drift

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Genetic diversity

• Evolutionary processes• Natural selection

A major mechanism of evolution.

Natural selection results from selective pressures in the environment (environmental pressure)

It acts as a filter for genetic variation: the best adapted individuals will survive and reproduce in greater numbers over time.

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Genetic diversityEvolutionary processesNatural selection

Peppered moth

• The peppered moth occurs in two color forms (light and dark forms)a. Both forms are displayed against an unpolluted, lichens-

covered tree.b. Both forms are displayed against a dark tree, on which the

lichens were killed by pollution.

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Genetic diversityEvolutionary processesNatural selection

Peppered moth

• In unpolluted areas, trees are covered in lichens and the light form of the moth is hard to see, and thus it is more common.

• After air pollution in mid 1800’s in British cities, trees were covered with coal dust, and the dark form became common and the light form rare.

• Thus, natural selection resulting from selective environmental pressure (here is air pollution) favors the survival of dark form.

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Genetic diversity

Evolutionary processesGene flow: A movement of alleles from one population to another through:

• Migration of individuals or gametes between populations of a species, and even between species.• Migration is adding or removing alleles from the population resulting in evolutionary change.

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Genetic diversityEvolutionary processesGenetic drift: is the change in allele frequencies as a result of random events.

• Random events could eliminate some alleles from the population, altering its allele frequencies. • In other words, a random event causes a certain genetic trait of individuals to become more common or rarer over time regardless the fitness of such individuals. • Thus, in contrast to natural selection, genetic drift doesn’t work to produce adaptations.

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Genetic diversityEvolutionary processesOccurrences of genetic drift: Genetic drift can be seen in the following example:

• An exploding volcano destroys almost all of the most common trees on a small island. Over time, the types of tree that were not affected by the volcano continue to flourish, while the once-common trees continue to dwindle.

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Genetic diversityEvolutionary processesA population bottleneck (bottleneck effect) is an example of genetic drift• A population bottleneck is a sharp reduction in the size of a

population due to environmental events (such as earthquakes, floods, fires) or human activities (overhunting, for example).

• A few individuals are available to contribute genes to the next generation.

• These individuals show reduced genetic variability and allele frequencies that are different from the parent population.

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Genetic diversityEvolutionary processesA founder effect is another example of genetic drift• A founder effect occurs when an isolated colony is started by a

few members of the original population.• A flock of birds or insects, for example, may become lost during

migration by a storm, and may settle on an isolated island.• There, only a few individuals contribute genes to the future

population, and may have allele frequencies that are very different from the frequencies of the parent population.

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Genetic diversity: the hidden face of biodiversity What is genetic diversity? Genetic diversity is the genetic variation within and between populations