3.03: PEDIGREES
Pedigrees
•
The risks of passing on a genetic disorder to
offspring can be assessed by
genetic counseling
,
prenatal testing
, and by analyzing a
pedigree
.
•
A
pedigree
is a family history diagram that shows
how a
trait
is inherited over several
generations
.
•
A pedigree can be mapped out to determine if
individuals are
carriers
or if their children might
inherit
the disorder.
•
Carriers are individuals who are
heterozygous
for
an inherited disorder but do not show
symptoms
.
Carriers can then pass the
allele
for the disorder
on to their
children
.
Pedigrees
•
In a pedigree,
females
are indicated by
circles, males are indicated by
squares.
•
Shaded
figures represent individuals
with the
trait
, a
carrier
could be 1/2
shaded (but not always!).
•
Generations
are numbered with roman
numerals (
I, II, III, IV
) from top to
bottom.
•
People
within generations are
numbered (1, 2, 3) from left to right.
•
People that are
married
(or just having
children together) are connected by a
horizontal
(left to right) line.
Offspring
of
individuals are connected to their
parents by a
vertical
(up and down) line.
Pedigrees
•
By analyzing a pedigree you can tell if a trait is
dominant or recessive and if it is
autosomal
or
sex
-
linked.
One parent has the disease, and none of
the three children inherited it. We can
tell that this is a
recessive
trait because
not many people in the family have it. If
it were a
dominant
trait, many more
would have inherited it.
Both males and females show the trait, so
we know this is not sex
-
linked but is an
autosomal
trait.
Pedigrees
•
We can also analyze a pedigree to
figure out people’s
genotypes
. If we
know this is an
autosomal
recessive
trait, then anyone shaded in must
have the genotype (
nn
). Anyone not
shaded must have either (
NN
or
Nn
).
•
What is the genotype of person
I
1?
nn
•
Person
IV
2?
Nn
or NN
•
Who in this pedigree must be
heterozygous?
III
1 and
III
2
•
Only
women
are
carriers, and only
men
show the trait.
Therefore, this must
be a
sex
-
linked
trait.
•
We can also tell this is a
recessive
trait, because
not many people have it. In order for a trait to
have carriers, it must be recessive. If a trait is
dominant
, people either have it or they don’t.
•
Since this is a sex
-
linked recessive trait, what is
the genotype of Alice?
X
H
X
h
•
What is the genotype of Fred?
X
h
Y
3.04:
KARYOTYPING
AND GENETIC
DISORDERS
Karyotypes
•
Genetic disorders may be detected by
using prenatal testing and pedigrees.
They can also be detected using
karyotypes
.
•
A
karyotype
is a photograph of an
individual’s
chromosomes
in a dividing
cell during mitosis. The chromosomes
are arranged by
size
and numbered.
Karyotypes
•
A
karyotype
can show you two things:
1.
Chromosome
abnormalities
:
missing
chromosomes,
extra
chromosomes, or if
chromosomes are malformed
2.
The
sex
of the person
Karyotypes
Normal
Karyotype
Down’s Syndrome
Genetic Disorders
Down’s Syndrome
:
o
A chromosomal disorder caused by an extra
chromosome 21
. For this reason it is also known
as
Trisomy
21
(which means 3 chromosome 21’s).
o
Caused by
nondisjunction
, which means that during
meiosis a gamete is produced with an extra copy of
chromosome 21. This is not an inherited trait, it
happens in the egg or the sperm before fertilization.
o
Symptoms: learning disabilities, developmental
disabilities, and impaired physical growth.
o
Occurrence: about 1 of every 9,000 births.
Genetic Disorders
Genetic Disorders
Cystic Fibrosis
:
o
Symptoms: causes thick
mucus
to coat the
lungs
leading
to severe breathing problems. It also causes the
pancreas to not secrete enzymes as efficiently as it
should, causing poor growth, diarrhea, and vitamin
deficiency.
o
Inheritance:
autosomal
recessive
disease caused by a
mutation in a gene.
o
Occurrence: 1 in 3,900 children are born with this
disease, and there is no cure.
Genetic Disorders
Genetic Disorders
Huntington’s Disease
:
o
Symptoms: a genetic neurological disorder
characterized after onset by uncoordinated,
jerky
body
movements and a decline in some mental abilities.
People with Huntington’s Disease have too many CAG’s
in a gene on their DNA and so form a
mutant
protein
from too many glutamines.
o
Occurrence: Up to 7 people in 100,000 have this
disorder.
o
Inheritance: This is an
autosomal
dominant
trait, so an
affected individual needs just one copy of the gene to
show the disease.
Genetic Disorders
Genetic Disorders
Sickle Cell Anemia
:
o
A blood disorder in which the
red blood cells
are not flexible
and round but are rigid and sickle
-
shaped (like a crescent
moon). This restricts the blood cells’ movement throughout
the blood stream and decreases the amount of
oxygen
the
cells can carry through the body.
o
Inheritance: a
recessive
trait.
o
Symptoms: misshapen blood cells cause the blood to not
carry enough oxygen throughout the body. Individuals most
often feel fine, but their lives are interrupted by periodic painful
attacks. The only treatment is pain medication during these
attacks.
o
Occurrence: 1 out of every 10 African
-
Americans has this trait.
Genetic Disorders
3.04: Biotechnology
3.04: Genetic Engineering
•
Genetic engineering
means making
changes
to an organism’s
DNA
code.
•
In a genetic engineering experiment,
scientists use the following techniques:
Genetic Engineering
1.
Cutting
DNA using
restriction enzymes
.
Restriction enzymes are bacterial enzymes
that bind to short sequences of DNA, then cut
the DNA between specific
nucleotides
.
•
Ex: the enzyme
Eco
R
I
recognizes the
nucleotide sequence GAATTC and cuts
between the G and A
ATTCACGA
GAATTC
TACCG
ATTCACGA
G
AATC
TACCG
Genetic Engineering
2. The DNA fragments are separated using
gel
eletrophoresis
. This creates a pattern of
bands made out of those DNA fragments.
These fragments can be put on a piece of
paper and made into a DNA fingerprint.
–
In gel electrophoresis, an electric
current
is run
through a gel containing the DNA.
Larger
sections of DNA move more
slowly
, and
smaller
sections move more
quickly
. In this
way, we get a banding pattern that is unique to
each person, since every person’s DNA is
different.
3.04: DNA Fingerprinting
•
A
DNA fingerprint
is the pattern of dark
bands that is made when a person’s DNA
restriction fragments
are separated by gel
electrophoresis.
•
Because restriction enzymes cut different
DNA sequences in different places, each
individual has a
unique
pattern of
banding
.
DNA Fingerprinting
•
Uses of DNA fingerprinting:
Can be
compared
to establish whether
people are related, such as in a
paternity
case.
Useful in
forensics
because it can use
DNA found in blood, semen, bone, or hair.
•
Useful in identifying the
genes
that cause
genetic disorders, such as Huntington’s
and Sickle Cell Anemia.
DNA Fingerprinting
DNA Fingerprinting
3.04: Cloning
•
Another type of genetic engineering that
you may have heard of is
cloning
.
Cloning means to create a population of
genetically
identical
cells from a single
cell.
•
In 1997, a Scottish scientist Ian
Wilmut
cloned a sheep by nuclear transfer. How
did he do it?
Cloning
1.
An
egg cell
was removed from a sheep
and the
nucleus
of the egg cell was
removed.
2.
The cell, now with no nucleus, was
inserted into a
donor cell
taken from a
different adult sheep.
3.
The fused cell began dividing and the
embryo
was placed into a foster mother
sheep where it developed normally.
Cloning
•
From this foster mother,
the cloned sheep
named
Dolly
was born.
She looked and acted
like a normal sheep and
even had a baby of her
own, but she died at an
early age. This
suggests that clones
may not have as long a
life expectancy
as the
organisms they come
from.
Cloning
•
Since then, scientists have cloned cows,
pigs, mice, and other
mammals
. They
have been cloning
bacteria
and other
microorganisms for much longer.
•
The use of cloning technology in
humans
is scientifically possible, but raises serious
moral and
ethical
issues.
3.04: Recombinant DNA
•
Genetic engineering very often involves
using
recombinant DNA
—
DNA made from
two
or more different
organisms
.
•
A great example of this is the making of
human
insulin
for diabetics. Insulin is a
protein hormone that controls sugar
metabolism. Diabetics don’t make enough
insulin and so must inject it. We used to
take insulin from the pancreases of
slaughtered cows and pigs, but now we
genetically engineer it.
Recombinant DNA
1.
The human
gene
for insulin is
cut
out of
the DNA using
restriction enzymes
and
transferred into bacterial DNA.
2.
The bacteria, now made of
recombinant
DNA since they contain human DNA along
with their normal bacterial DNA, then
transcribe and translate the human insulin
gene using the same code a human cell
would use in order to make human insulin.
Recombinant DNA
•
This is very
efficient
: since bacteria
reproduce
much more quickly than
animals do, they can produce much more
insulin.
•
This is also how we make other drugs,
like Factor VII to help hemophiliacs’ blood
to clot, and vaccines for viruses like
smallpox and polio.
Recombinant DNA
•
When scientists use recombinant DNA
technology they create
transgenic
organisms
. This is a plant, animal, or
bacteria that contains another organism’s
DNA. The bacteria that takes on the
human insulin gene becomes a transgenic
organism.
Recombinant DNA
Transgenic Organisms
3.04: Human Genome Project
•
The
Human Genome Project
was a research
project that was completed in 2003.
Scientists from 6 different countries identified
all of the
base pairs
that compose the DNA of
a human. They identified all
3.2 billion
base
pairs of DNA that make up the human
genome.
•
The goal of this project was to better
understand human DNA to find
causes
and
cures
for common diseases.
Human Genome
•
Here is what they found:
Only 1 to 1.5 percent of the human genome is
genes
—
DNA
that codes for
proteins
. Each
human cell contains about
6 feet
of DNA, but
less that
1 inch
is made of genes. These
genes are scattered about the genome in
clumps.
Human cells only contain about 30,000 to
40,000 genes. This is only
double
the amount
that a fruit fly has.
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