Download Human Genome

Human Genome
Chapter 14
Sections 1-3
14-1 Human Heredity
• Karyotype – a picture of chromosomes arranged in
homologous pairs.
Humans have 46 chromosomes:
23 from the male
23 from the female
44 autosomes
2 sex chromosomes
• Autosomal Chromosome – (Autosomes) the 44
chromosomes in a Karyotype that are not sex
chromosomes.
• Sex Chromosomes- determine an individual’s sex
Females have 2 copies of a large X chromosome.
Males have 1 X & 1 small Y chromosome.
Male vs. Female
• Males and Females are born in a roughly 50:50
ratio because of the way in which sex
chromosomes segregate during meiosis.
• Females produce human egg cells that carry a
single X chromosome.
• The female inherits 1 copy of every gene located
on each X chromosome.
• Half of all sperm cells carry an X chromosome
and half carry a Y chromosome.
(50% XX, 50%XY)
Mendelian Genetics
• Biologists must identify an inherited trait
controlled by a single gene.
• Establish that the trait is inherited and not a result
of environmental influence.
• Study how the trait is passed from one generation
to the next.
• Use a Pedigree Chart.
Pedigree Chart
• Pedigree – chart that shows the relationships
with in a family.
Ex. Pg. 342, fig. 14-3
• The inheritance of a certain trait in a family can
be traces using a pedigree.
• It shows how a trait can be passed from one
generation to the next.
• It determined whether an allele is dominant or
recessive.
• The circle represents a Female and the square
represents a Male.
Figure 14-3 A Pedigree
A circle represents
a female.
A horizontal line connecting
a male and female
represents a marriage.
A half-shaded circle
or square indicates
that a person is a
carrier of the trait.
A completely
shaded circle or
square indicates
that a person
expresses the
trait.
A square represents
a male.
A vertical line and a
bracket connect the
parents to their children.
A circle or square
that is not shaded
indicates that a
person neither
expresses the trait
nor is a carrier of
the trait.
Genetic Traits
• Polygenic – controlled by many genes.
None are dominant.
Ex. Shape of eyes and ears, height, skin color, and eye
color.
• Many traits are strongly influenced by
environmental factors like nutrition and
exercise.
Ex. Height is largely determined by genetic factors, but
nutritional improvement can increase the average height.
Human Genome
• The first human genes to be identified were
those that control blood type.
• Red blood cells carry 2 different antigens called
A and B.
• Antigen – molecules that are recognized by the
immune system.
Ex. ABO blood groups and Rh blood groups.
• ABO – single gene w/ multiple alleles (3)
Ex. I ,I ,i. I and I are codominant, and i is recessive.
A
B
A
B
• Rh –single gene w/ 2 alleles.
Ex. Rh(+) has the antigen and Rh(-) does not have the antigen.
Blood Types
• There are 4 possible blood types:
• A, B, AB, O
Genotypes
I ,I
I,I
I,i
I,I
I,i
i,i
Pg. 344, fig. 14-4
A
B
A
A
A
B
B
B
Phenotypes
produce AB (both antigens)
produce A
produce A
produce B
produce B
produce O (no antigens)
Figure 14-4 Blood Groups
Section 14-1
Phenotype
(Blood Type
Genotype
Antigen on
Red Blood Cell
Safe Transfusions
To
From
Human Genetic Disorders
Pg. 345, fig. 14-6
• PKU (Phenylketonuria)
– One of the first discovered.
– Lacks and enzyme that breaks down an
amino acid found in milk.
– When phenylalanine builds up, it causes
mental retardation.
– Caused by a recessive allele from both
parents.
Human Genetic Disorders
• Tay-Sachs Disease
– Results in nervous system breakdown.
– Death in the first few years of life.
– Caused by a recessive allele.
Human Genetic Disorders
• Cystic Fibrosis
– Result of a deletion of 3 bases in the middle
of the protein sequence which causes the
protein to fold improperly.
– It messes up the order because bases are
removed.
– Digestive problems & thick, heavy mucus
clogs the lungs.
– Caused by a recessive allele.
Figure 14-8 The Cause of Cystic Fibrosis
Section 14-1
Chromosome
#7
CFTR
gene
The most common allele
that causes cystic fibrosis is
missing 3 DNA bases. As
a result, the amino acid
phenylalanine is missing
from the CFTR protein.
Normal CFTR is a chloride
ion channel in cell
membranes. Abnormal
CFTR cannot be transported
to the cell membrane.
The cells in the person’s airways
are unable to transport chloride
ions. As a result, the airways
become clogged with a thick
mucus.
Human Genetic Disorders
• Huntington’s Disease
– Loss of muscular control and mental
deterioration.
– Symptoms appear later in middle ages.
– Caused by a dominant allele.
Human Genetic Disorders
• Sickle Cell Anemia
– Red blood sell are shaped like sickles.
– Shape causes cells to get stuck in the vessels
and blood not to flow.
– Tissues are damaged and severe weakness.
– Linked to malaria in Africa.
– Only 1 DNA base is changed in the allele.
– Codominant allele.
14-2 Human Chromosomes
Chormosomes # 21 and # 22
• The smallest chromosomes.
• The first 2 chromosomes to have their sequence
identified.
• #21 - 32 million DNA base pairs, 225 genes, responsible
for ALS (Lou Gehrig’s disease).
• #22 – 43 million DNA base pairs, 545 genes, responsible
for many genetic diseases, Leukemia, and tumor
causing diseases of the nervous system.
• Both have spaces on the chromosome that do not code
for proteins. These spaces are unstable sites where
rearrangements occur.
• Genes located close together on the same chromosome
are linked and will be inherited together.
Sex Linked Genes
Genes that are located on the X and the Y chromosomes.
Pg. 350, fig. 14-12
• X Chromosome – more than 100 sex linked genetic
disorders occur here.
• Y Chromosome – smaller and has fewer disorders.
• Colorblindness, Hemophilia, & Muscular Dystrophy are
expressed in males even if they are recessive.
• To appear in a female, it must have 2 copies.
• Are passed from fathers to daughters & to then to their
sons.
Sex Linked Genetic Disorders
Colorblindness
• Genes are defective on the X
chromosome causing the inability to
distinguish certain colors.
• Red – Green - 1:10 males, 1:100.
• Males have 1 X chromosome so all alleles
are expressed even the recessive.
Sex Linked Genetic Disorders
Hemophilia
• Problem on the gene that controls blood
clotting.
• Protein missing.
• 1:10,000 males
• May lead to death from minor cuts or
internal bleeding from bumps.
• It can now be treated with injections.
Sex Linked Genetic Disorders
Duchenne Muscular Dystrophy
• Progressive weakening and loss of
skeletal muscle.
• 1:3,000 males born in U.S.
X – Chromosome Inactivation
• Since males only have 1 X chromosome, the female has
to make adjustments for having 2 X chromosomes.
• In females – one X chromosome is randomly turned off.
• It forms a dense region in the nucleus called a Barr body.
• Males don’t have Barr bodies because their X
chromosome is active.
• Ex. Calico Cats- X chromosome carries the allele for
coat color and can carry more than 1 color. The X
chromosome is turned off in many different places
causing several colors to appear. Anytime you see a cat
with multiple colors, it will most likely be female. Males
are only 1 color
Chromosomal Disorders
Nondisjunction – most common error to occur in meiosis.
Pg. 352, fig. 14-15
• “Not coming apart”
• If the chromosomes do not pull apart, an abnormal
numbers of chromosomes find their way into the
gametes throwing off the number and order.
• Involves autosomes, sex chromosomes, and
homologous chromosomes.
Downsyndrome Pg. 353, fig. 14-16
• An extra copy of chromosome # 21(3 copies – trisomy)
• 1:800 babies in the U.S.
• Produces mild – severe mental retardation.
Sex Chromosome Disorders
Caused by Nondisjunction
• Turner’s syndrome – female inherits only 1
X chromosome. Women is sterile & her
sex organs don’t develop.
• Klinefelter’s syndrome – extra X
chromosome interferes with meiosis &
prevents reproduction. Ex. XXXY, XXXXY.
• As long as a Y is present, the offspring will
be male.
Nondisjunction
Section 14-2
Homologous
chromosomes
fail to separate
Meiosis I:
Nondisjunction
Meiosis II
14-3 Human Molecular Genetics
DNA Fingerprinting – individuals are identified by analyzing
sections of DNA.
• No 2 people, except identical twins, have exactly the
same DNA.
• Determine whether blood, sperm, hair, or other
materials left at crime scene matches suspects.
• 1990- Human Genome Project – Goal was to identify the
DNA sequence for the entire DNA in a human cell.
• 2000- Human Genome was sequenced by looking for
overlapping regions b/w sequenced DNA fragments.
Locating Genes
Section 14-3
Gene
Sequence
Promoter
Start
signal
Gene
Stop
signal
Figure 14-18 DNA Fingerprinting
Section 14-3
Restriction enzyme
Chromosomes contain large
amounts of DNA called repeats
that do not code for proteins.
This DNA varies from person to
person. Here, one sample has
12 repeats between genes A
and B, while the second
sample has 9 repeats.
Restriction enzymes are used
to cut the DNA into fragments
containing genes and repeats.
Note that the repeat fragments
from these two samples are of
different lengths.
The DNA fragments are
separated according to size using
gel electrophoresis. The
fragments containing repeats are
then labeled using radioactive
probes. This produces a series of
bands—the DNA fingerprint.
Human Genome
• Able to find causes of genetic disorders.
• Used to cure genetic disorders by using
gene therapy.
• It cannot tell if an allele is dominant or
recessive.