Transcript Chapter 1 - Brimm Medical Arts High School

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Human Genetics: concepts and applications
5th edition
Ricki Lewis
Chapter 1
Overview of
Genetics
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Genetics
is the study of inherited variation and
traits…GENEALOGY = looking at familial
relationships
Genetic information is transmitted at several levels…
DNA
Genes
Chromosomes
Genome
Individual
Family
Population
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Deoxyribonucleic acid (DNA)
A polymer consisting of a chain of nucleotides
Nucleotide components:
• Phosphate
• Sugar
• Base:
Guanine
Adenine
Thymine
Cytosine
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G
A
T
C
A DNA double helix
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Genes
• are the basic unit of inheritance.
• are composed of DNA (deoxyribonucleic acid).
• direct the formation of proteins via biochemical
instructions.
Different versions of the same gene are called alleles.
Alleles result from the process called mutation.
Some traits are determined nearly entirely by GENES;
Most traits also have environmental components
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The genome
is the complete set of genetic information
characteristic of the organism.
The genome includes:
• all of the genes present in an organism (Exons)
• other DNA sequences that do not encode genes
(called introns)
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The human genome
• consists of 3 billion base pairs of DNA
• includes 28,000 to 34,000 genes
• is organized as 23 pairs of chromosomes
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Principles of Genetics
• Affects our lives on a greater scaled
than other studies of science
• Touches history, politics, economics,
sociology, art, and psychology
• BIOETHICS = a field of study that
addresses many of the personal issues
that arise in applying medical
technology
– Examples of bioethical issues?
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Genomics
• New field of study
• The study of the functions and
interactions of many genes at a time
• Allows for comparison between
humans and other species
• Addresses the more common
illnesses influenced by many genes
that interact with each other and the
environment
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Genetic Testing
• Personal Choice
• Tests may look for gene variants known to
cause illness or DNA sequences statistically
associated with increased risk of developing
a particular condition in a particular
population
• Tests taken to prevent, delay, control, or
treat symptoms that have a high probability
of occurring or to gain information, perhaps
to make decisions about whether to have
children or not
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DNA Microarray
• DNA is extracted and cut into pieces, then
tagged with molecules that fluoresce under
certain types of light
• Genetic material is then applied to “DNA
chips” (postage-stamp-sized pieces of glass
or nylon) with particular sequences of DNA
attached
• The genes on the chip are aligned in fixed
positions  This is called a DNA
MICROARRAY
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After the Test…
• Cardiovascular disease is the largest
and most diverse
• A genetic counselor is a person who can
interpret the test results and sit down
with the patient and let them know the
proper information
• The tests are customized to what
information the person is looking for
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DNA
•
•
•
•
DNA makes up genes
RNA = intermediate language
RNA aids in manufacturing proteins
PROTEOMICS = considers the proteins
made in a particular cell type
• 1.5% of DNA in human genome
encodes proteins
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Mutations
• Some cause disease
• Some provide variation (ie. Freckles)
• Some = no visible effect because
encoded protein not changed to affect
its function
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Polymorphisms
• Polymorphisms = a variant in DNA that is
present in at least 1% of a population
• SNPs (single nucleotide polymorphisms)
= single base sites that differ among
individuals
• DNA microarrays can isolate these and
mutations
• SNP patterns detected are associated
with disease risk
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Chromosomes
DNA is organized in discrete segments called
chromosomes
Humans have 23 pairs of chromosomes:
22 autosome pairs which are the same in both sexes
1 pair of sex chromosomes, the X and the Y
Each chromosome includes hundreds of different genes.
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A karyotype
is a chart of the chromosomes organized
by the size of the chromosome pairs.
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Karyotypes
• Chromosomes are stained with dyes
or fluorescent chemicals bound to
specific DNA sequences to create
different patterns, which can reveal
abnormalities
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Cells, Tissues, Organs
• All cells EXCEPT red blood cells contain
all of the genetic instructions
• Differentiation = process that causes
cells to differ in appearance and function
(only use some of their genes)
• Cells, tissues, organs, organ systems
• Stem cells = less specialized cells that
can produce other ones or differentiate
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Individuals carry two alleles of each gene.
Genotype is the combination of alleles that an
individual possesses. (what is present)
Phenotype is the visible trait that results in a
particular genotype. (what you see –
appearance; what happens)
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Allele types
• Dominant = an allele that produces
an effect when present in just one
copy
• Recessive = must be present on both
chromosomes to be expressed
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Somatic versus germline cells
Somatic cells comprise the majority of an
individual’s body.
• During development distinct types of cells
make proteins using different subsets of genes.
Germline cells within the testis or ovary produce
gametes (sperm or ovum)
• Germline cells retain the ability to form all of
the types of cells, both germline and somatic cells.
Together somatic cells and germline cells
comprise the entire body of an individual.
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The Family
Inheritance of traits can be observed in
families.
A pedigree indicates the structure of a family
schematically.
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The Family
• A person = 50% biological mom & 50%
biological dad
• 50% in common with siblings
• 25% in common with each grandparent
• First cousins share one-eighth of their
genes
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A population
is a group of interbreeding individuals who
possess a particular collection of alleles
or gene pool.
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Between species/Evolution
Comparison of DNA sequences indicates the amount
of similarity between two species.
98% of human DNA sequences are shared with
chimpanzee.
Many genes present in humans are also present in
mice, fish, fruit flies, yeast, and bacteria.
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Very similar
On average two random people share the same DNA
sequence in 99.9% of their genome.
Studies of variation among humans indicates
humans arose in Africa and migrated across the
globe with relatively little change.
and very different
On average two random people differ at 3 million base
pairs
(approximately one nucleotide of every thousand).
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Traits can be determined predominantly by one gene.
Mendelian traits result from variation in alleles
of one gene.
Traits can be determined by multiple genes.
Polygenic traits result from variation in several
genes.
Traits can be determined by genes and environment.
Multifactorial traits result from effects of one or
more genes and the environment.
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Do Not Function Alone
• Knowing whether a trait or illness is
Mendelian or multifactorial = important
for predicting the risk of reoccurrence
– Mendelian = simple calculation
– Multifactorial = difficult; too many factors
• Environmental factors = alter gene
expression
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• Predictions of inherited disease are
considered in terms of “modified
genetic risk” which takes into
account single genes & the
environment and family history
• GENETIC DETERMINISM = the idea
that an inherited trait is
unchangeable and its appearance
inevitable (countered by
environmental factors)
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Risk Calculations…
• Prediction = NOT precise science
• Genetic counselors calculate risks for
clients who want to know the risk
• Risk Factor = threatening situation
• 3 types of risk calculations…
– Absolute
– Relative
– Empiric
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Absolute Risk
• Probability that an individual will
develop a particular condition
• Odds and percentages are used to
depict
• More defined
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Relative Risk
• Likelihood that an individual from a
particular population will develop a
condition in comparison to individuals
from another group
• Expressed in ratio
• Absolute / general population = RR
• Less than 1 = less risk than population
• Greater than 1 = greater risk than
general population
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Empiric Risk
• From population level observations
• Example = 1 in 100 risk of having a
second child with an extra
chromosome
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Applications of Genetics
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Identity
forensics
paternity testing
Health care
prediction of disease
development of treatments
family planning
Agriculture
crop and animal breeding
genetically modified foods
pest management
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Agriculture
• Biotechnology = the use of organisms
to produce goods or services
• Enables researchers to manipulate one
gene at a time, adding control and
precision to agriculture
• “Genetic Engineering”
• Creates genetically modified (GM) foods
(or transgenic organisms)
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Genetically modified foods
Rice modified by the addition of the beta-carotene gene,
a precursor of vitamin A, stores more iron than unmodified
rice.
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Global Perspective
• Cannot be considered solely as a
branch of life science (affects humans
so intimately)
• Genetics and genomics are rapidly
spawning technologies that promise to
vastly improve quality of life
• For next couple of years not popular
(cost and not widely available)
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