Modern Genetics

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Chapter 4

• Modern Genetics

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Read page 112, paragraph 1 to yourself.
Traits can be controlled by either 1 gene, or by
multiple alleles.
Some traits controlled by 1 gene Widows peak,
dimples
Traits can be controlled by multiple alleles (3
or more forms of a gene that code for a single
trait)
Examples height is controlled by 4 genes Skin
color is controlled by 3 or more genes.
Another example of multiple alleles is blood
type. Look at page 113 paragraph 4. Read this
to yourself. We will then discuss it.
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For Blood types, there are 4 possibilities A, B,
AB, and O
A and B are codominant, while O is recessive.
Remember, even though a gene may have multiple
alleles, a person only can carry 2 of these
alleles. Why?
You can only get 1 from Mom and 1 from Dad!
Some genes act together as a group to produce a
single trait.
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Effects of Environment
Certain traits can be effected by things other
than your parents.
For example, height can be effected by diet.
Since the 1800s, the average height for a person
has increased by 4 inches due to having a better
balanced diet, better medical care, and living
conditions.
Give some examples of how diet, living
conditions, or medical care have improved since
the 1800s.
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Gender
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Sex-linked genes
Some traits occur more often in one gender than
the other. The genes are carried on the X Y
chromosomes.
One example is red-green colorblindness- a person
can not distinguish red from green. Take the
test below, or on page 116 of your book.
Males are affected more than females. Why?
See the Punnett Square on page 117
Carrier a person who has 1 recessive allele and 1
dominant allele. The carrier does not have the
condition, but could pass it on to offspring.
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Pedigree
A tool geneticists use to trace the inheritance
of traits- they look at a single trait in a
specific family.
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Genetic Disorders
An abnormal condition that a person inherits
through genes or chromosomes. These are caused
by mutations or changes in a persons DNA.
A condition where the body produces abnormally
thick mucus in the lungs or intestines.
Cystic Fibrosis
The mutation is carried on a recessive allele.
This mainly affects people with ancestors from
Northern Europe.
Four babies a day are born with CF in the
United States.
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Sickle-Cell anemia
A genetic disorder that affects the production of
hemoglobin which is found in the blood.
See the picture below, or on page 120 of your
book, and look at the punnett square in your
notes.
Sickle-shaped blood cells can NOT carry as much
oxygen as normal cells, and because of their
shape they become stuck in narrow blood vessels.
This causes the person to have pain and weakness.
Occurs most often in people of African ancestry.
About 9 of the African American population carry
the allele for this disorder.
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Hemophilia
A sex-linked genetic disorder in which a persons
blood clots very slowly, or not al all.
This means a person with this disorder could
bleed to death from a minor cut. (yes, even a
paper cut!)
Hemophilia is caused by a recessive trait on the
X chromosome, and hence affects more men than
women. Why? (see punnett square in your notes)
Treatment for this disorder includes doses of the
missing clotting protein, and avoidance of
contact sports or other activities.
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A persons cells have an extra copy of chromosome
21, caused by an error during meiosis.
Down Syndrome
People with Down Syndrome have a distinctive
physical appearance, some mental retardation, and
heart defects (which can be treated).
See page 122 of your book for a picture of the
chromosome, and another picture of the physical
appearance.
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Human Inheritance
Human traits
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Diagnosing Genetic Disorders
2 tools doctors can use to detect genetic
disorders are amniocentesis and karyotypes (dont
worry about the 2nd one).
A procedure in which a doctor removes some of the
fluid surrounding a developing baby using a long
needle.
Amniocentesis
Genetic counseling
Helps couples understand the chances of having a
child with a particular genetic disorder.
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Advances in Genetics
There are 3 methods people have used to develop
organisms with desirable traits. They are
Selective breeding
Cloning
Genetic engineering
The process of choosing a few organisms with
desired traits to serve as parents of the next
generation.
Selective breeding
This was used more than 5,000 years ago in
Central Mexico. People saved seeds from plants
that produced the best food. By doing this
repeatedly, they developed a crop we now call
corn.
This process is used for the following reasons
increase the value of plants or animals (i.e.
cows are bred to produce more milk, or plants are
bred to resist disease or pests).
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A selective breeding process that involves
crossing 2 individuals that have identical or
similar sets of alleles.
inbreeding
One goal of inbreeding is to produce breeds of
animals with specific traits (like purebred race
horses or pure blooded dogs).
Inbreeding can lead to a reduction in new allele
combinations which can lead to problems like hip
defects in certain breeds of dogs.
Breeders cross 2 genetically different
individuals to obtain the best traits of both
parents. For example, a farmer crossing an ear
of corn with many kernels with one that is
resistant to disease.
Hybridization
There is a problem with this. The breeder can
not control whether the trait will be passed on
or not.
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An organism that is genetically identical to the
organism from which it was produced. (The DNA is
exactly the same.).
Cloning
Animals are cloned by taking an egg cell and
replacing the nucleus with one from another
animal, and then implanting it into a third
animal.
Plants can be cloned through a cutting- a small
part of a plant, like a leaf or stem, is cut from
the plant, and the piece then grows into a new
plant.
This was first done with a sheep named Dolly.
It took over 200 attempts before it worked!
Uses pigs are being cloned with genes that will
make their organs suitable for transplant into
humans. Can you think of other uses?
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Genetic engineering
Genes from one organism are transferred into the
DNA of another.
This is sometimes called gene splicing as DNA
molecules are cut open and a gene from another
organism is spliced into it.
This is used to produce medicines, improve food
crops, and may cure human genetic disorders.
Genetic Engineering in Bacteria
See page 129 for how genetic engineering works.
This can be used to produce insulin for
diabetics, or human growth hormone for kids whose
bodies do not produce enough.
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Genetic Engineering in Other Organisms
Scientists have inserted genes from bacteria into
cells of tomatoes, wheat, rice and other crops to
enable them to survive in colder temperatures, or
in poor soil conditions, and to resist insect
pests.
Scientists can insert human genes into cow
cells-this can help produce the blood clotting
protein for hemophiliacs.
Gene therapy
Involves inserting working copies of a gene
directly into the cells of a person with a
genetic disorder (this is still experimental).
For example, scientists can insert gene codes for
proteins into harmless viruses and then place the
altered viruses where they are needed - lungs for
people with Cystic Fibrosis
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DNA Fingerprinting
Enzymes are used to cut a DNA sample found at a
crime scene into fragments. Electricity then
separates the fragments into bands -- each
persons DNA pattern is unique -- and then
compared to a suspects DNA
The Human Genome Project
All the DNA in one cell of an organism. The
human genome is about 3 billion DNA base pairs.
Genome
The main goal of the Human Genome Project is to
identify the DNA sequence of every gene in the
human genome. This may help scientists
understand how humans develop from a fertilized
egg into an adult, what makes the body work, what
causes problems, and new treatments or prevention
strategies for genetic disorders or diseases.