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Modern Genetics
Table of Contents
Human Inheritance
Human Genetic Disorders
Advances in Genetics
Modern Genetics
Human Inheritance
-Many human traits are controlled by a
single gene with two alleles: one
dominant and one recessive
*Examples: widow’s peak, smile
dimples, hitch-hikers thumb,
curved pinkie.
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-Other human traits are controlled by
single genes with multiple alleles.
*This means more than two
alleles exist for a trait.
*However, you still only inherit
two alleles
*Example: Human Blood Type
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-Three alleles are involved: A, B, and o.
-A and B are both dominant (co-dominant)
-O is recessive
-Blood type A can have genotypes AA or Ao;
-Blood type B can have genotypes BB or Bo;
-Blood type AB can have only genotype AB
-Blood type O can have only genotype oo
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-Finally, a lot of human traits are
controlled by many genes that act
together. This is called, Polygenic
Inheritance.
*Examples: eye, skin, and hair
color, height, weight, body build,
and shape of eyes, lips, and
ears.
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Skin Color Graph and Punnett Square
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The Sex Chromosomes
One pair of chromosomes determines
the sex of an organism.
The larger chromosome in the pair is
the X chromosome. The smaller is
the Y.
XY = male
X
Y
X
X
XX = female
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-Egg cells from a female contain
only X chromosomes.
-Sperm cells from a male can
contain either an X or a Y. So it is
the father who determines the sex of
the child depending on which sperm
cell fertilizes the egg
Modern Genetics - Human Inheritance
Modern Genetics
Sex-Linked Traits
-The sex chromosomes carry genes that
make a person male or female.
-They also carry genes that determine
other traits.
-These traits are usually more common
in men because they are carried on the X
chromosome. The matching gene on the
Y chromosome is missing.
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-They are called Sex-Linked Traits.
-Examples:
*Color-blindness and Hemophilia
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Punnett Sq. with Sex-Linked Traits
Color Blind Male marries a Normal Female
Xc Y x
XX
None of their
X
X
Xc
Y
XcX
XY
Xc X
XY
kids will be
color blind.
However, any
girl they have
will be a
carrier.
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Human Genetic Disorders
-A genetic disorder is an abnormal
condition that a person inherits.
Information for the disorder is
carried on chromosomes just like
other genetic information.
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-Examples:
*Cystic Fibrosis—genetic disorder in
which the body produces too much
mucus in the lungs and intestine. It
is homozygous recessive. 1/20
Caucasians carry a recessive allele.
It is caused by a 3 base deletion in
the DNA molecule.
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*Sickle-Cell Anemia—genetic disorder in
which red blood cells have an unusual
sickle shape. RBC’s can’t carry as
much oxygen and can clog arteries.
The allele is codominant with the normal
so you must have two alleles to produce
ONLY sickle-shaped RBC’s. More
common in African americans (1/400).
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Sickle-Cell
RBC
Normal RBC
How sickle cells cause
blood clots.
Modern Genetics - Human Genetic Disorders
Sickle-Cell Disease
Click the Video button to watch a movie about
sickle-cell disease.
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*Hemophilia—genetic disorder in which
blood clots slowly or not at all. It is a
homozygous recessive sex linked trait
carried on the X chromosome. So it is
more common in men than women.
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*Down Syndrome—caused by an extra
21st chromosome. Results in some
degree of mental retardation. Heart
defects and other physical conditions are
also common.
Children with
Down Syndrome
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Pedigrees
-A pedigree is a chart that tracks
which members of a family have a
particular trait.
-The trait can be an ordinary trait or
a genetic disorder.
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These are the symbols used on a
Pedigree chart.
= female with the trait being studied.
= female without the trait being studied.
= male with the trait being studied.
= male without the trait being studied.
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Half-colored figures represent
carriers.
Horizontal lines represent
marriages or matings.
Vertical lines represent children or
offspring.
Modern Genetics - Human Genetic Disorders
Modern Genetics - Human Genetic Disorders
A Hemophilia Pedigree
The pedigree shows the inheritance of hemophilia, a sexlinked disorder in a family.
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Advances in Genetics
-Three genetic techniques allow
people to produce organisms with
more desirable traits.
-They are:Selective breeding,
Cloning, Genetic engineering
Modern Genetics - Advances in Genetics
Selective Breeding
Click the Video button to watch a movie about
selective breeding.
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Selective Breeding
-Selective Breeding—selecting
organisms with desired traits to be parents
of the next generation.
-Two types:
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*Inbreeding—the crossing of closely
related organisms.
Self-pollination in plants is an
example.
Purebred animals are an example.
It is a way of keeping desirable
traits in a breed.
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Problems:
Organisms are too genetically similar
and tend to be susceptible to diseases.
Inbred animals have difficulty
adapting to environmental changes.
Certain undesirable traits become
common because they form pairs
during fertilization.
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Hybridization—the crossing of two
genetically different individuals.
Results in offspring that have
characteristics of both parents.
Organisms are more genetically
different and are therefore likely to
be stronger and healthier than
inbred organisms. This is especially
true in hybrid plant varieties.
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Problems: Many times the organisms
produced are sterile.
Examples:
Tigon—cross
between a
female lion and
a male tiger.
Mule—cross between a
donkey and a female horse.
Liger—cross between
a male lion and a
female tiger.
Modern Genetics
Just for Fun---Check these out!!!
What if you could
cross a golden
retriever with a
bald eagle…
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a great
dane and a
horse…
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A bull
dog and
gorilla…
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a penguin
and a
housecat…
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a sparrow
and a
tiger…
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a pug and an owl…
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an
orangutan
and a
mutt…
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or a ram, a
gorilla and a
German
Shepard?
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Cloning
Clone —an individual that is
genetically identical to and has only
one parent.
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Cloning
-Cloning plants is easy and has
been done for many years.
-Just take a cutting from a stem,
give it water until it sprouts roots,
then plant it. You have a clone of the
first plant.
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-Another technique is
called vegetative
propagation. Here you
take branches from one
plant and graft them onto
other plants.
-Many seedless fruits are
grown this way.
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Animal Cloning
-The first
successfully cloned
animal was a
tadpole, cloned in
1952. It was
cloned from
embryonic cells.
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-In February 1997, Ian Wilmut, a
Scottish scientist, successfully
cloned an adult sheep.
*The sheep’s name was Dolly.
*Dolly was cloned from a
mammary cell taken from her
mother.
She was the only lamb to
Dolly was the first animal
survive from 277 eggs.
cloned from an adult
animal.
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In sexual reproduction, a child gets half its genes from its mother (in her egg)
and half from its father (in his sperm cell).
Cloning is a type of asexual reproduction. All the child’s genes would come from
a body cell of a single individual.
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In order for the embryo to develop, the reconstructed
egg must be treated with chemicals or electric
current to get the cells to divide.
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Two types of Cloning : Reproductive
and Therapeutic
-Reproductive Cloning produces an embryo
which is implanted into a female’s womb with
the intent to produce a fully formed offspring
*Dolly was produced this way.
(Dolly was put down on Feb. 14, 2003. She
suffered from lung cancer and crippling
arthritis. She was 6 yrs old. Most Finn
Dorset sheep live to be 11-12 yrs. old).
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-Other successfully cloned mammals
include: goats, cows, mice, pigs,
cats, rabbits and a guar.
-Attempts to clone other species such
as monkeys, chickens, horses, and
dogs have been unsuccessful
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Therapeutic Cloning is the production of embryos
for use in research. The cloned embryos are not
placed in a female to be carried to term, but are
used to generate stem cells which can then
create tissues and organs.
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-This cloning uses the nucleus of a body cell to
grow new skin, nerve, or muscle cells—or
any type of cell needed.
-These cells will be genetically identical to the
other cells, so the body will not reject them.
-This would improve the success of transplant
surgeries.
-Researchers also believe that one day stem
cells can be used as replacement cells to
treat heart disease, Alzheimer’s, cancer, and
other diseases.
Modern Genetics
Risks of Cloning
-Reproductive Cloning
*Expensive
*Highly inefficient (90% of cloning
attempts fail)
*Cloned animals seem to be less healthy
*May be premature aging problems
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*Therapeutic Cloning
-Ethical concerns about harvesting and
terminating human embryos.
-May lead to “designer babies”
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Genetic Engineering
-In genetic engineering, genes from one
organism are transferred into the DNA of
another organism.
-This process can be used to produce
medicines (like insulin), to improve food
crops, and in gene therapy (to cure
people of genetic diseases).
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The Human Genome Project
-Began in 1985.
-First draft is complete.
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-A genome is all the DNA in one cell
of one organism.
-Project goal—to identify the DNA
sequence of every gene in the
human genome.
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DNA Fingerprinting
-This technique was developed
in1984 by Professor Sir Alec Jeffreys
of England.
-It is used to identify people and
show whether people are related.
-Unless you are an identical twin,
your DNA is unique.
Modern Genetics - Human Inheritance
Colorblindness Punnett Square
Modern Genetics - Human Inheritance
Inheritance of Blood Type
Blood type is determined by a single gene with three alleles.
This chart shows which combinations of alleles result in each
blood type.
Modern Genetics - Human Inheritance
Identifying Main Ideas
As you read the section “Patterns of Human Inheritance,”
write the main idea in a graphic organizer. Then write three
supporting details that further explain the main idea.
Main Idea
Human traits are controlled by single genes with two alleles, single
genes with multiple alleles, and multiple genes.
Detail
Detail
Detail
Human traits
controlled by single
genes with two
alleles have two
distinctly different
phenotypes.
Though a single
gene can have
multiple alleles, a
person can carry
only two of these
alleles.
Multiple genes that
control a trait act
together to produce
a single trait with a
large number of
phenotypes.
Modern Genetics - Human Inheritance
Links on Genetics
Click the SciLinks button for links on genetics.
Modern Genetics
End of Section:
Human
Inheritance
Modern Genetics - Human Genetic Disorders
Pedigree Activity
Click the Active Art button to open a browser window and
access Active Art about pedigrees.
Modern Genetics - Human Genetic Disorders
Comparing and Contrasting
As you read, compare and contrast the types of genetic
disorders by completing a table like the one below.
Disorder
Cystic fibrosis
Description
Cause
Body produces
abnormally thick
mucus.
Red blood cells are
sickle-shaped and have
reduced ability to hold
oxygen.
Recessive allele due to
removal of three DNA
bases
Hemophilia
Blood clots slowly or not
at all.
Recessive allele on X
chromosome
Down Syndrome
Mental retardation and
heart defects
An extra copy of
chromosome 21
Sickle-cell disease
Codominant allele
Modern Genetics
End of Section:
Human Genetic
Disorders
Modern Genetics - Advances in Genetics
Changing Rice Production
The graph shows how worldwide
rice production changed
between 1965 and 2000. New,
hybrid varieties of rice plants are
one factor that has affected the
amount of rice produced.
Modern Genetics - Advances in Genetics
Changing Rice Production
Reading Graphs:
According to the graph, how
did rice production change
between 1965 and 2000?
Rice production increased.
Modern Genetics - Advances in Genetics
Changing Rice Production
Reading Graphs:
How many metric tons of rice
per hectare were produced in
1965? How many were
produced in 2000?
2 in 1965; 4 in 2000
Modern Genetics - Advances in Genetics
Changing Rice Production
Calculating:
Calculate the approximate
difference between rice
production in 1965 and 2000.
2 metric tons/hectare
Modern Genetics - Advances in Genetics
Changing Rice Production
Developing Hypotheses:
What factors besides new
varieties of plants might help
account for the difference in
rice production between 1965
and 2000?
Possible answer: fertilizers
and improved harvesting
methods
Modern Genetics - Advances in Genetics
Genetic Engineering
Scientists use genetic engineering to create bacterial cells
that produce important human proteins such as insulin.
Modern Genetics - Advances in Genetics
Asking Questions
Before you read, preview the red headings. In a graphic
organizer like the one below, ask a question for each
heading. As you read, write answers to your questions.
Questions
What is selective breeding?
Answers
Selective breeding is the process of
selecting organisms with desired traits
to be parents of the next generation.
Why are organisms cloned?
To produce offspring with desired traits
What is genetic engineering?
A process in which genes from one
organism are transferred into the DNA
of another organism
What advance has helped us learn
about human genetics?
The Human Genome Project
Modern Genetics - Advances in Genetics
Links on Genetic Engineering
Click the SciLinks button for links on genetic engineering.
Modern Genetics
End of Section:
Advances in
Genetics
Modern Genetics
Graphic Organizer
Human traits
controlled by
Single genes
Multiple
alleles
Many genes
Sex-linked
genes
such as
such as
such as
such as
Widow's peak
Blood type
Height
Colorblindness
Modern Genetics
End of Section:
Graphic Organizer