Crash Course Genetics


Since ancient times, man seeks
to understand how does the transmission of characteristics
from one being to another. The first ideas about heredity
were quite simple and only said the children
were similar to parents, without understanding the
mechanism behind this finding. Genetics is the part of biology
that studies heredity, that is, the way the features are passed
on from generation to generation. It is considered that this science
began with the experiments and laws proposed by a monk named Gregor
Mendel, in a paper published in 1866. Mendel expected, with the development
of his work with peas, understand why the cross between hybrid generated
such different descendants. According to some authors, these works,
Mendel intended to create ways to develop hybrid plants that retain essential
characteristics for agriculture. To carry out their work, Mendel chose
peas and analyzed seven characteristics: the size of the plant, seed
texture, seed color, pod shape, color pod, flower
color, and flower position. The choice of the plant is essential for the
success of their research since one pea develops through an easy cultivation, seeds,
and various short reproductive cycle. One of the laws proposed
by Mendel in his work was the segregation of factors,
known today by genes. According to the researcher, each
person has a couple of factors for each characteristic that separates
the time of formation of gametes. At the moment of fertilization,
the gametes of father and mother come together,
taking its features. Mendel contributed in a big way
for studies of genetics and, therefore, is today considered
the father of this science. The work of this research, however,
were overlooked for many years. However, in 1900, researchers
Correns, Tschesmak, and De Vries independently rediscovered Mendel’s
work to study hybrid plants. These three botanists contributed
to the acceptance of Mendel’s ideas and the early
genetic studies in humans. Another work worth mentioning is the Morgan,
who has studied the Drosophila fly and understood that the transmission of certain
characteristics was determined by sex. His work gave particular
attention to the changes and their transfer
to the descendants. In 1926, the researcher published the
book The Theory of the Gene, in which he explained that heredity is linked to
units passed from parents to children. What is Genetics Genetics is the branch of biology
that studies the transfer of physical and biological characteristics
from generation to generation. Many scientists believe
that the explanation for many genetic problems
lies in the genes. Heredity is the genetic
inheritance we received from our ancestors, whether,
physical or even diseases. Hence, the explanation of children
resembles the father, mother, grandfather, grandmother, uncle, aunt
and even more distant relatives. Another way to observe heredity
is by crossing a plain coat of white mouse with a
black rat bristling fur. The puppies from this cross
will indeed be born black and bristly hair, because of the
black rat genes are stronger; however, when these pups reach adulthood,
they may have smooth white coat pups. It is due to the mixing of genes they have. There are currently a lot of
research on the genetic code. Scientists believe that the result of
these studies, in the future it will be possible to eliminate many genetic diseases
that affect many people worldwide. Classification of Genetic Diseases 1- monogenic They are caused by changes
or mutations that occur in the DNA sequence
of a single gene. Also known as Mendelian disorders. Examples of conditions: Sickle Cell anemia Duchenne Miotómica Duchene Muscular Dystrophy Huntington’s Disease Tay-Sachs disease phenylketonuria Cystic fibrosis hemophilia A Familial hypercholesterolemia thalassemia Marfan’s syndrome Chromosome 2 Structural and numerical changes
occur across a whole chromosome. Examples of conditions: Down’s syndrome trisomies: 18 13 X Cri-du-chat syndrome (cat meows) Klinefelter Syndrome Turner Syndrome Wolf-Hirschhorn syndrome XYY syndrome 2- multifactorial They are caused by
combinations of environmental factors and mutations
in multiple genes. Also known as Complex
or polygenic disorders. The Multifactorial Inheritance is
also associated with some hereditary characteristics (fingerprint patterns,
height, eye color, skin color). Examples of conditions: Alzheimer Congenital malformations Congenital heart diseases Certain types of cancer diabetes mellitus Arterial hypertension Obesity What is the human genome We can say that the genome is the human
genetic code, i.e., the set of human genes. The genetic material we can
find all the information for the development and functioning
of the body of a man. This genetic code is present
in each one of the cells. The human genome is
shown for 23 pairs of chromosomes which interiorly
contains the genes. All information is encoded by
the DNA, deoxyribonucleic acid. This acid, which has a double helix shape
consists of four bases are joined in pairs: adenine with thymine and
cytosine with guanima. The Human Genome Project
(HGP) is one of the greatest achievements
in human history. It is translated as an effort of
international research to sequence and map all the genes of human beings, which
as a whole is known as the genome. Integrated into the HGP,
similar efforts have been used to characterize the genomes
of many other organisms, since most of the living
organisms have many genes that are homologous or similar,
or with similar functions. The identification of sequences and
functions of the genes of these organisms is reflected in the potential to explain
the homology of the genes in humans, can thus be used as an animal
model in biomedical research. The hereditary material (genome) of all
multi-cellular organisms is the double-stranded molecule of deoxyribonucleic
acid (DNA – deoxyribonucleic acid), which
contains all our genes. The HGP formally launched
in 1990 and designed to last 15 years, had as
its primary objectives: To determine the order, or sequence,
of all the bases of our genomic DNA; identify and map the genes of all
23 pairs of human chromosomes; store this information in databases,
developing efficient tools to analyze these data and to develop ways to use this
information to study biology and medicine. The HGP began as an initiative of the
public sector, and the leadership of James Watson, then the head of the
National Institutes of Health (NIH). Numerous schools, universities, and labs
are participating in the project, using resources from the NIH and the Department
of North American Energy (DOE). 18 countries have initiated research
programs on the human genome. The largest programs are
developed in Germany, Australia, Brazil, Canada, China, Korea,
Denmark, USA, France, Holland, Israel, Italy, Japan,
Mexico, United Kingdom, Russia, Sweden and
the European Union. With the entry of private initiative in
the Genome Project, giving preference to a targeted approach only to genes that
are pertinent to the cure of diseases, the public sector has to
review your schedule, and the sequencing process
has been accelerated. In February 2001, simultaneously with the
announcement of the US company Celera, the HGP announced the first draft containing
the sequence of 3 billion base pairs, about 90% almost complete
human genetic code. The number of genes, according
to the calculations of both teams of
researchers, are little more than 30,000,
significantly lower than initially thought (50
to 140 thousand genes). The results were published
in two different journals. The British magazine Nature published the
work of HGP researchers, led by Francis Collins, current director of NHGRI (National
Human Genome Research Institute), and the US Science, the work of Celera
researchers, led by scientist Craig Venter. Expected to end in 2003, two years
earlier than initially thought, Francis Collins called the
publication of the almost complete sequence of the human genome in
2001 as “the end of the beginning”. He explained in a recent article NHGRI: “A critical understanding
of gene expression, the connection between sequence
variations and phenotypes, protein-protein interactions
on a large scale and comprehensive analysis of human
biology will happen now… For me as a doctor, the exact
result of the HGP will be able to improve the diagnosis, treatment,
and prevention of diseases and most of the benefits that
are yet to happen for humanity. With this wide variety of data
sequences in hand, we can achieve those purposes that we could never
have imagined a few years ago” (Francis S. Collins Genomics:.. The
coming revolution in medicine.pdf; From Global Agenda, the magazine of the World
Economic Forum Annual Meeting 2003). The utility of the human genome Through genetic mapping of
the human genome will be possible very soon discover
the cause of many diseases. Many medicines and vaccines
could be developed from the information obtained
by genetic research. Finding the cause of various diseases, the
human being may adopt preventive measures. Through genetic testing and
research, it is possible to detect whether a human being is predisposed
to suffer from certain diseases or if an embryo has
inherited serious diseases. Soon, when they discovered the functions of
all human genes, other benefits will come. Main areas of genetics Molecular Genetics –
emphasizes the study of the structure and function of
genes at the molecular level. Genetic discoveries or the application
of genetic concepts in our daily life. They are daily in the media
and some of the most striking developments have occurred in
the field of Medical genetics. Currently, geneticists understand
the metabolic basis of hundreds of hereditary disorders
are known defective genes that result in various diseases
inherited, study aspects of our behavior and our personality that are
controlled by our genetic make-up, research the role that genes may have in
behaviors such as alcoholism and sexuality and have known for some time that genes Defective
are the cause of some mental disorders. Today, dominant tenure tools
for molecular genetic analysis researchers
are aimed to identify genes which, when broken, make individuals
more susceptible to these diseases. Molecular genetics is also providing
new ways to treat disease. During decades, diabetics receiving insulin
obtained from animals, usually pigs. Today, insulin is produced in bacteria
possessing the gene for human insulin. Growth hormone, human, isolated before
carcasses, it is also produced by bacteria and is used to treat children who do not
produce sufficient amounts of the hormone. Many other proteins medical importance
today, are routinely produced in bacteria that have been transformed
with the appropriate human gene. Genetic research is also conducted in the
field of nutrition and techniques Molecular are used to enhance the quality and
production of foods (Genetically modified). Findings of genetic
research initiated several commercial aspects of the
biotechnology industry. Companies that manufacture pharmaceuticals
and tests diagnosis, or that provide services such as DNA profiles have
contributed to the world economic growth. Some forms of cancer are familial
or hereditary, and others occur sporadically among all
members of a population. However, all cancers are genetic
diseases in the sense that are caused by changes in the genetic information that
is transmitted to the daughter cells. The available evidence
indicates that all cancers result from the
accumulation of damage the genes that control or
influence cell proliferation, cell differentiation,
and related processes. Although there are hundreds of
different types of cancer, all have a thing in common: the loss of normal
control of cell multiplication. The mutant genes cause an
increased risk of cancer, and they are being identified
and studied intensely. As we learn more about the function
of these genes in normal situations and abnormal, we come closer to
effective therapeutic treatments. Forensic science has used genetic
techniques in molecular legal matters. The DNA isolated from a small sample
of tissue, sometimes only one sperm, or Leukocyte hair follicle
recovered from the scene of a crime may be subjected to a detailed
analysis Molecular and the results can be used to identify
or delete the suspect. Gene Therapy (introduction of genes into
normal cells of patients with genes defective) offers great promise for the
effective treatment of inherited diseases. Therapy gene has been used in
conjunction with other therapies, although the introduced genes were
expressed for only a short period. Although there are reasons
to expect gene therapy to be ultimately successful in the
treatment of genetic disorders, the results today indicate
that more research is needed to determine
how and why genes work. They are soon off after
coming into new host cells. The Human Genome Project aims to
map and sequence all the material Genetic human and certain other
organisms are genetically important. The knowledge the structure of the
entire genetic information of humans and other organisms will
have profound effects on society. This information will have marked
effects on the ability of scientists to diagnose and create effective
treatments for human disease. Thus, this information should have
a positive impact on human health. However, it also creates
complex problems moral, ethical and legal
to be faced by people. Classical Genetics Genetics uses procedures and techniques
before the arrival of Molecular Biology. Genetics is dedicated to studying
the genes, which in turn comes from heredity, genetics, and
the variety of genetic traits. The name “genetics” is Greek
Genno, and it means to be born. That being the focus of study in this
area, their research is focused on the DNA, RNA, chromosomes, and is a
field linked with molecular biology. Just as there is a Molecular
Biology, Molecular Genetics exists. Their study is focused
on the molecular level. It is a prominent area within molecular
genetics, through molecular information, can set seed standards and evaluate the
correct classification of living things. This classification is a
molecular system call. Some researchers in this field point
to life as the set of strategies used by RNAs, for multiplication
and conservation of themselves. The genetic history is
closely linked to Mendel. Gregor Mendel pioneered in
studying heredity characteristics. His early studies were with peas. Experience sought evidence that
the flow characteristics from one generation to another followed
a logic, calculation, a ratio. His work had great help in the genetic
construction, especially after his death, and the practice of
statistical genetics has to be used. Further back in history, we
can consider 1859, the year that Charles Darwin published
the Origin of Species. Seven years later, Gregor Mendel
also published something critical to genetics: their study “Experiments
in plant hybridization”. In 1913, Alfred Sturtevant set up the
first genetic map of a chromosome. Robert W. Holley, Har Gobind, and
Marshall W. Nirenberg, to have deciphered the genetic code and noted its importance
for the production of proteins, won the Nobel Prize in physiology
or medicine of the same year. In 2003, 99% was published mapped the human
genome (to an accuracy of 99% accuracy), and years ago (1989) was the
first time a human gene was mapped by Francis
Collins and Lap-Chee Tsui. Genetics is usually remembered by so-called
recessive genes and dominant genes. These such genes “recessive” and
“dominant” is the explanation of some characteristics are more likely to present
themselves inherited than others. An example is the eye color. Light eyes are typical of
recessive genes, as dark colored eyes are dominant
gene characteristics. In a hypothetical situation, a blue-eyed
woman with a husband of black eyes. The son of this couple will
have a great chance of being born with dark eyes instead of
blue eyes, like his mother’s. That’s because black eyes,
as the parent, are dominant genes, while the mother’s
eyes are recessive genes. There is a small possibility
of the baby being born with clear eyes, but it is much less
than the other possibility. Within the field of genetics,
there are specific areas: classical genetics (the period
before the coming of Molecular Biology) is a phase that had
not yet much knowledge. Much of classical genetics ideas were cast
aside with the following year discoveries. His main contribution was the discovery
on the Mendelian inheritance. Molecular genetics has,
as stated above, a more focused activity to the
molecular level of genetics. Population genetics is a branch
of genetics that studies the human adaptation to
the conditions around us, the changes that have been according to our
adaptation to the conditions we live in. Another area within the
gene is quantitative. It studies the functions
of the qualities gained by genes, using these
data to form statistics Population Genes Studying the changes that occur in
the alleles with the influences of evolutionary forcesshow the process which
is now regarded as popular genetics. The populations are an evolutionary
drive, whereas there is evolution when the frequency of genes in this
population will change significantly. However, from an ecological point of
view, a population amounts to only a group of individuals occupying a given
geographical area at a given time. This type definition
easily deduces that can not serve as an evolutionary
drive because it does not imply that the beings reproduce, the
fundamental condition for genetic change. For this reason, the evolutionary unit is
conventionally called Mendelian population, that is, a community of individuals who
share the certain genetic background. It is formed, therefore, for individuals
related to mating, descent or ancestry. The genes that constitute the
genetic background – the set of all genes present in a
population at a given time are transmitted from
generation to generation, random and new
combinations of alleles. It easily follows that is the
genetic background of the parents that derives at random, the genetic
background of the descendants. The greater the number of genes that
comprise the genetic background of the population, the greater the likelihood
there is variation in the next generation. The determination of the gene frequency of a
population in successive generations shows whether or not the genetic background
maintenance if developments are acting factors. The Hardy-Weinberg law refers
to Mendelian populations in balance, i.e., infinitely
large populations, in which the crossings
occur randomly (panmixia), and there are
factors of evolution. Accordingly, the Hardy-Weinberg
law says that the frequency of each allele tends to remain
constant in each generation. However, this is not the case in reality! Populations evolve over generations, which
leads us to the obvious conclusion: the Hardy-Weinberg law does not
apply to real situations because there are always growing factors
acting on the population. Genes do not divide in meiosis
always accurately (mutation), the genotypes are not transmitted
to uniform rates (selection), populations are not infinitely
large, and the crossings are not random (genetic drift) and populations
are not isolated ( migration). All these factors tend to change
the balance of populations by altering the gene frequencies, then
are called factors of evolution. Evolution Factors The enormous variety
of factors that can change the genetic
composition of populations, only five of them are
considered capable of causing significant deviations,
including the following: Mutation There are three main types of mutation: Gene mutations are changes of some
base pairs in the DNA molecule; Structural changes are number of
changes or gene arrangement on the chromosome (deletions, duplications,
inversions or translocations); Numerical mutations are changing
the number of chromosomes, either monosomy (2n-1), polysomies (2n
+ 1) or nullisomics (2n-2). The monosomy and nullisomics
are deadly, while polysomies cause severe disabilities,
physical and mental. Examples of this are the cases of
trisomy 13, 18 or 21, the syndromes of Turner (XO), Klinfelter (XXY)
and super masculinity (XYY). The effect of these mutations in
the gene frequencies depends on upon the adaptability that
patients were presenting them both for survival and for playback in the
middle of the species environment. If the mutation is neutral may
persist for many generations. It can be assumed that genetic
variability (various alleles for a gene, for example) is the consequence
of the accumulation of mutations because these are the only known variability
source of the genetic background, other developments factors only rearrange
variability create nothing again. Despite all the mutation it can not change
the direction of evolution because it occurs at rates of 3×10-6 order in spontaneous
mutations, only creates variability. Development results of the action on the
population and thus on individuals with mutations of the most powerful evolution
of factors such as natural selection. The action on harmful mutated genes
varies with the dominant and recessive. Recessive genes, harmful or
otherwise, are only active in the homozygous state, while ruling also
act in the heterozygous state. Thus, similar to mutation rates
detrimental recessive genes are kept in a larger amount in the genetic background
of the population that dominant, since the heterozygous
carriers of these genes do not express any inferiority
to homozygous normal. It is considered that genetic variability
has superiority in heterozygous or hybrid effect, the most important
factor for remaining in populations. In this situation,
heterozygotes are better adapted to their environment
that homozygous, thus conserving the population of harmful
alleles in the homozygous state (sickle cell anemia, for example, homozygosity causes
an 80% mortality before the adult stage. The anemic heterozygotes
are a population response to selective pressure
by malaria parasites). In these instances, the harmful allele
is recessive but not codominant. Migration Populations are isolated between them but
may occur migration – moving subjects of reproductive age from one population
to another, resulting gene flow. These movements can be input –
immigration – or output – emigration. If migrants survive and
reproduce, they contribute their genes to the genetic background
of the host population. Sometimes migration rate is very
low, working as a mutation affecting the gene bit rate, but if it can
provide sufficiently high variability and function as a primary factor in the
development, the pair of natural selection. Obviously, migration affects
only the genetic background of a population from an evolutionary point
of view if the migrant population is different from the
receiving population and / or to introduce an allele
“especially coveted.” TOP Crossings not random In natural populations crossings can
be random – panmixia – a situation in which the frequency of alleles
in a population remains unchanged. However, this usually this
is not so, for maintaining the genetic background would
the absence of evolution. In an average population,
only some individuals reproduce, usually more
showy males, for example. The organizations selected its
partners, focusing their similar and close, increasing homozygosity and
giving rise to genetic defects. This fact means that, in the human
population, marriages between members of the same family are considered incestuous
and generally legally prohibited. An extreme case of this is
self-pollination in plants. Genetic drift Genetic drift is the change
of the genetic background, at random, from
generation to generation. Usually, this occurs in people whose actual
player is less than 100 individuals (the population may be large but only a small
number to play, you get the same phenomenon). This problem may result from the separation
of larger populations due to geographical, climatic barriers (during
certain times of the year the population may
be attributable to numerous good condition,
being more or less decimated in changing
station) or other influences. Thus, it is easy to predict that each
of these small populations does not contain a total sample of the genetic
background of the original population. These deviations may lead to the
disappearance of certain alleles and attachment of other, quite by accident,
regardless of their fitness. This reduction in variability
by eliminating alleles in small populations reduces adaptability
to environmental changes, which can lead to the
decline of the species, by attachment less
favorable alleles. This problem currently
exists with bison, cheetahs, elephant seals and other
endangered organisms, where only a small number,
usually in zoos reproduce. An extreme case of genetic drift
is the founder effect in which a very small number of individuals
(or even just a pregnant female) moves to another habitat,
carrying only part of the genetic heritage of
the original population. It is common in the colonization
of islands from the mainland. Studies in human populations revealed
the resulting founder effect of the migration of a small religious group
from Germany to the United States, which remained isolated from
the rest of the population. Natural Selection The natural selection can
be defined as a difference in viability and fertility
of the individual. Many of the changes outlined above
are unfavorable or even lethal but its accumulation is contradicted
by the selection as the mutant with unfavorable characteristics
which will be eliminated. Darwin’s theory considers
that only part of the seed survives and reproduces
(differential viability), and different couples
produce different numbers of viable offspring
(differential fertility). Thus, holders of features with
greater adaptive capacity are most survivors, and the following
generations will tend to increase. In a population, recalling the usual
distribution of traits, being the highest point of the curve
(mean value for the feature) called point adjustment or
calibration (ideal value for this medium at that time), there are
three types of natural selection: Stabilizer – maintaining
the homogeneity of the population because the extreme
phenotypes are eliminated. It indicates a well-adapted
to medium population, and this means that remains
more or less stable. Studies have revealed the action of this
type of selection in humans, showing medium size babies have a greater probability
of survival that very large or slight. Another known situation is the
effect of storms on birds, which are preferably dead individuals with
very large or minuscule wings; Directional – most common
situation, there is a tendency to move the set point, favoring
the extreme phenotypes. It indicates environmental
changes, being selected the best organisms adapted
to this new medium. Known examples of this are the resistance
to antibiotics by microorganisms or insecticides, as well as the ever-present
case of the peppered moth-butterflies; Disruptive – the action of selection
occurs eliminating the intermediate phenotype, the most common, favoring extreme
characteristics outside the setpoint. May give rise to a balanced
polymorphism (two or more phenotypes in the population) or, in extreme
cases, two different species. Examples of this type of
action on the populations can be observed in plants
growing near mines, where the well-demarcated
contamination of certain areas leads to the development
of two types of plants (one can live in contaminated areas but
is small, while large on you can do). Further a case in poultry derives
from the fact that in some locations the only possible power
supply are seed or insect larvae. It leads to the birds are
selected with larger and stronger nozzles
(for starting seeds) and birds with nozzles beautiful
and delicate (suitable will search larvae in
holes in tree trunks). A bird with a beak through would
have difficulty obtaining food. As mentioned above, the
directional and disruptive selections are
considered evolutionary. This analysis of trend
factors can be concluded that the natural
selection and migration are important factors in
controlling Microevolution (simple changes in gene frequency
in the local population). The selection, by itself, is the
conductive agent of progressive changes larger (appearance of new taxa
– Macroevolution). Such changes are the result of hundreds
or thousands of microevolution, joined and extended by the selective
pressure of the environment. Ecological Genetics – analyzes and
studies the genetics taking into account the interactions of organisms and
between them and the environment. Genomics – studies the genetic
patterns of certain species. Genomics is the science that studies
the genome of organisms from its complete sequence, to understand its
structure, organization and function. The sequencing of the genome of animal
species, including the human genome, and vegetables have provided evidence
for synteny studies of gene functions. This science is divided into structural,
functional and comparative. The structural genomics studies the
organization and structure of genes, analyzing transcribed and
structural sequences using methodologies such as DNA
sequencing and markers. The study of gene functions
is up to functional genomics, which attempts to understand the changes
in the functioning of the genome at different stages of development and under
different environmental conditions. The studies of gene
function rely on the construction of cDNA
libraries and techniques such as Differential Display
Reverse transcriptase – PCR Serial Analyses of Gene
Expression Microarray. Linking and complementing these
two studies comes comparative genomics which seeks to understand
the relationships between genomes, the homology between sequences
and genes, determining the degree of synteny
of related species. These molecular tools provide
the Improvement Classic a breakthrough in the search for
individuals genetically superior for allowing regions or genes that
control identified be interest. Assisted Improvement can follow the
phenotypic variation of the characteristics and location of QTLs, candidate
genes and greater effect of genes. Identified the gene, you can select for
or against the pre-existing genotype, or obtain new genotypes through the silencing
or overexpression of genes of interest. Thus, genomics comes as a very important
tool for genetic improvement programs.

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