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Section 14-1
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Interest Grabber A Family Tree
To understand how traits are passed on from generation to generation, a
pedigree, or a diagram that shows the relationships within a family, is used. In a
pedigree, a circle represents a female, and a square represents a male. A filledin circle or square shows that the individual has the trait being studied. The
horizontal line that connects a circle and a square represents a marriage. The
vertical line(s) and brackets below that line show the child(ren) of that couple.
1.Which parent has
attached ear lobes?
2.How many children
do the parents have?
Which child has
attached ear lobes?
Go to
Section:
3.Which child is
married? Does this
child’s spouse have
attached ear lobes? Do
any of this child’s
children have attached
ear lobes?
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14–1 Human Heredity
A. Human Chromosomes
Section 14-1
B. Human Traits
C. Human Genes
1. Blood Group Genes
2. Recessive Alleles
3. Dominant Alleles
4. Codominant Alleles
D. From Gene to Molecule
1. Cystic Fibrosis
2. Sickle Cell Disease
3. Dominant or Recessive?
Go to
Section:
Chapter 14-1 - Human Heredity
Review - Gametes, zygote How are human traits
inherited?
How many chromosomes do humans have?
Autosomes? How many sex chromosomes?
Pedigree - a chart which shows how traits are carried in
a family. (see overhead and p. 342/343).
These are the “papers” which animals have to show their
blood line.
Link to Ben
Karyotype Pictures of your chromosomes organized by
size. Homologues are put together. Extra or missing
chromosomes can be seen.
Male or female?
Figure 14-3 A Pedigree
Section 14-1
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.
Who has the disorder?
Multiple alleles
Human Blood groups have 3 alleles of the gene that code for
the trait of blood type. (1901) A B O alleles form 4 different
blood types. Red blood cells can contain a coating and
antigen (A B). Cells with and without the antigen produce the
four blood types.
(see overhead) A mixture of blood types in a transfusion can
lead to death.
Rh blood groups - Rh factor contains the Rh antigen and can
cause problems when given Rh- people were given Rh+ blood.
This trait is also controlled by multiple alleles (8).
Transfusion activity! - Who will survive?
Discontinuous variation - two categories of phenotypes by
dominant and recessive.(tall and short pea plants)
Continuous variation- many genes are responsible for wide
variation of phenotypes. (human height)
Human height variation
continuous variation
Figure 14-4 Blood Groups
Phenotype
(Blood Type
Genotype
Antigen on
Red Blood Cell
Safe Transfusions
To
From
Complex Inheritance and Human Heredity
Polygenic Traits
 Polygenic traits arise from the interaction
of multiple pairs of genes.
Autosomal disorders:
Recessive Alleles -Many disorders are causes by recessive alleles and do not
turn up in the population regularly due to this. The protein the gene codes for is
not made in the homozygous recessive form. See examples below.
PKU (Phenylketonuria) can cause mental retardation due to lack of enzyme phenylalanine hydraoxylase. 1 in 18,000 chance.
Albinism- four genes control pigmentation in humans. An example of
Epistasis- One of the four genes in recessive form effects the other three even
though they are at different loci. Pigment is not deposited.
Cystic Fibrosis - Disorder where excess mucus is made in lungs,
digestive system, liver, etc. There is an incorrect chloride channel Protein.
An example of Pleiotropy- one gene product can have harsh secondary effects)
Tay-Sachs link video clip- nervous system disease
Ellis-van Creveld Syndrome- (polydactylism and dwarfism). Example of
founder’s effect- Amish sect in Penn. Reproductively isolated for 200+ years.
One member had recessive allele. 1960’s-43 of 8,000 people in sect had this
disorder.
Complex Inheritance and Human Heredity
Albinism
 Caused by altered genes (epistasis),
resulting in the absence of the skin
pigment melanin in hair and eyes.
 White hair
 Very pale skin
 Pink pupils
Complex Inheritance and Human Heredity
Epistasis
 Variety is the result of one allele hiding the
effects of another allele.
eebb
eeB_
No dark pigment present in fur
E_bb
E_B_
Dark pigment present in fur
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.
Dominant Alleles - disorder is found in heterozygous and homozygous
dominant form. (See overhead)
Ex: Achondroplasia - a genetic disorder of bone growth caused by a
dominant allele. Type of dwarfism where the person is less than 4 foot 4
inches. (see webpage)
Huntington Disease - (H) disorder where a person’s nervous system
begins to break down, progressive loss of muscles and mental function. It
usually hits in ages 30-40. The defective gene has too many copies of the
codon CAG for glutamine. Tests are now available to determine if you have the
diseased allele or not. Many people choose not to get the test.
Fact: It is believed that this disease originated from one Dutchman who settle in
South Africa in 1658. All affected persons were directly or indirectly related to
this man. This is called the founder affect and found in remote small
populations.
Also found in a Venezuela group that was brought there 200 years ago with a
European sailor.
*Would your children have a good chance of having this if you did?
Two versions of Sickle Cell Anemia
1. Full disease - SS genotype
All RBC have sickle shape. All hemoglobin of the blood is affected very serious injury or death. RBC get stuck in capillaries due to their
abnormal shape.
2. Carrier - AS heterozygous genotype. This person has
characteristics of normal and sickle cell. They have only a few effects
of the disease. These people are partially resistant to Malaria, a
parasite which invades and destroys RBC. Would there be an
advantage to be a carrier in tropical areas?
If the full disease is deadly, why sickle cell is still around today?
This is called a genetic antimalarial disease. Many people say that
evolution stopped long ago, yet this disease has only been evolving for
the last few centuries as a genetic defense. In preventing one disease,
it causes another.
Codominant Alleles - both alleles are expressed.
Sickle Cell Anemia - The gene which causes this differs by one (RNA)
nucleotide (GUG instead of GAG). This, in turn, causes Valine to be
substituted for glutamic acid and changes the beta globin protein in the
hemoglobin in the red blood cells. It makes the proteins sticky and form chains
(polymerization) and RBC take on a sickle-like shape. The gene for normal (A)
and sickle cell (S) are codominant.
Gene Therapy- genes which produce gamma globin when added to the
incorrect beta globin protein, keep polymerization from happening and the RBC
from becoming Sickle shaped in mice experiments, (Seppa, 2000)
Translocation ---> humans?
Chimps, gorillas and orangutans- all have 24 pairs of chromosomes-humans23pairs. Did humans lose the 24th? No- humans have a large #2 chrom.
Which is a perfect match for the 2 different chromosomes found in apes,
chimps and oran. if they are fused together to form one chromosome.
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There are two potential naturalistic explanations
for the difference in chromosome numbers either a fusion of two separate chromosomes
occurred in the human line, or a fission of a
chromosome occurred among the apes.
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The evidence favors a fusion event in the human line. One
could imagine that the fusion is only an apparent artifact of
the work of a designer or the work of nature (due to
common ancestry). The common ancestry scenario
presents two predictions. Since the chromosomes were
apparently joined end to end, and the ends of
chromosomes (called the telomere ) have a distinctive
structure from the rest of the chromosome, there may be
evidence of this structure in the middle of human
chromosome 2 where the fusion apparently occurred. Also,
since both of the chromosomes that hypothetically were
fused had a centromere (the distinctive central part of the
chromosome), we should see some evidence of two
centromeres.
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Human Chromosome 2 and its analogs in the apes - from
Yunis, J. J., Prakash, O., The origin of man: a
chromosomal pictorial legacy. Science, Vol 215, 19 March
1982, pp. 1525 - 1530
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Section Outline
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Section 14-2
14–2 Human Chromosomes
A. Human Genes and Chromosomes
B. Sex-Linked Genes
1. Colorblindness
2. Hemophilia
3. Duchenne Muscular Dystrophy
C.X-Chromosome Inactivation
D.Chromosomal Disorders
1. Down Syndrome
2. Sex Chromosome Disorders
Interest Grabber
Section 14-2
1. On a sheet of paper, construct a Punnett square for the following
cross: XX x XY. Fill in the Punnett square. What does the Punnett
square represent? According to the Punnett square, what percentage
of the offspring from this genetic cross will be males? What
percentage will be females?
2. On a sheet of paper, construct a Punnett square for the following
cross: XXX x XY. Fill in the Punnett square. How is this Punnett
square different from the first one you constructed? What might have
caused this difference?
3. How do the offspring in the two Punnett squares differ?
Go to
Section:
Complex Inheritance and Human Heredity
Sex Determination
 Sex chromosomes
determine an
individual’s gender.
 Males XY
 Females XX
Sex-linked Inheritance(14-2) Nondisjunction link
(Y chromosome -carries the information which produces
maleness in humans. A hormone (TDF) is released in human
males at 6/7th weeks gestation. The presence or absence of this
protein determines the sex of the child.
Disjunction disorders - Sex chromosomes do not separate
properly during meiosis. Sperm and eggs have extra
chromosomes. Occurs in 1/1000 births.
1. Turner syndrome - XO genotype. Female is sterile.
2. Klinefelter syndrome - XXY genotype. Males are sterile with
immature sex organs and some female characteristics.
3. Metafemale - XXX genotype . Females tend to have learning
disabilities and may enter menopause early or have cycle
irregularities. Most have no affects from this.
What union of gametes would have produced the above
disorders?
4. XYY - Normal male, but may be taller than average.
Controversy about these males being antisocial and aggressive
and a link to some crimes.
Nondisjunction
Section 14-2
Homologous
chromosomes
fail to
separate
Meiosis I:
Nondisjunction
Meiosis II
X-linked Disorders
1. Red/Green Colorblindness - In Caucasians, 8% males and 1% females
are affected. Color blind test
2. Hemophilia -AHF protein for blood clotting is missing. This is also called
the bleeder’s disease. 1/10,000 males and 1/100,000 females get inherit this
disorder. Treatment is done by removing AHF from normal blood and injecting
it.
Could this be risky?
Fact: 18 out of 69 of Queen Victoria’s descendants were affected with
hemophilia. (England Early1800’s) Why was this so? What did royalty tend to
do to keep the crown in the family?
3. Muscular Dystrophy- Gene controlling this is made of 2 million base pairs.
Correct protein (dystrophin) contributes to muscle cell’s surface structure.
Mutant gene causes the wasting away of skeletal muscles. Many types of MD.
Duchenne’s is usually fatal by age 20 due to cardiac failure. 1 in 4,000 males
effected.
4. Mitral Stenosis - heart valve defect
Figure 14-13 Colorblindness
Section 14-2
Father
(normal vision)
Normal
Colorblind vision
Male
Female
Mother
(carrier)
Go to
Section:
Daughter
(normal
vision)
Son
(normal
vision)
Daughter
(carrier)
Son
(colorblind)
Sex- influenced traits - Baldness occurs more often in males than in
females. It could be due to the differences in male and female hormones.
X-Chromosome Inactivation- in females each cell randomly “turns off”
an X chromosome. The inactive X of each individual cell becomes a
“Barr Body” in the nucleus.
Ex: Calico Cats - only in females. A different X is inactivated in different
groups of cells to produce two different colors (one from each X) Can’t
happen in humans-pigment genes aren’t on the X chromosome.
Do males have Barr Bodies?
Down’s Syndrome - Chromosome disorder where individuals have an
extra 21st chromosome. Also called trisomy 21. 1out of 800 babies are
born with this (older age of the mother is a factor- more likely to carry an
abnormal fetus to full term and/or older eggs). Caused by nondisjunction during meiosis.
Testing for disorders- amniocentesis and chorionic villi sampling.
Section 14-3
•
Section Outline
14–3 Human Molecular Genetics
A. Human DNA Analysis
1. Testing for Alleles
2. DNA Fingerprinting
B. The Human Genome Project
1. Rapid Sequencing
2. Searching for Genes
3. A Breakthrough for Everyone
C. Gene Therapy
D. Ethical Issues in Human Genetics
Go to
Section:
Human Molecular Genetics (14-3)
Genetic tests can find the presence of “diseases” recessive alleles.
Testing for Alleles: (person is a carrier). The DNA code for the
recessive allele is slightly different than the normal allele.
Ways to test:
1. DNA Probes- used to detect special DNA sequences of disease
causing alleles (sequence is known)
2. Change in Restriction Enzyme cutting sites
3. Comparing lengths of alleles
DNA Fingerprinting- Uses DNA repeats to identify a person. DNA
from hair, blood, skin, etc. can be used. Repeats do not code for
proteins and differ among individuals. These repeats are cut out of
the DNA code by restriction enzymes. Radioactive probes label the
fragments and are separated by electrophoresis according to size.
(the shorter- the farther it can move). Each set of migrated repeats
produces unique banding patterns for comparison.
Human Genome Project- Video clip Human genome project
*Sequenced all of the DNA code for humans.
*Completed in June 2000.
*Computers were used.
*Estimate of only 31,000 genes. No longer believe one
gene, one protein. One gene may make many different
proteins.
*3 billion base pairs make up the human genome.
Gene Therapy - Can genes be changed? Yes and no.
Experimental- the faulty gene is replaced with a normal
gene. Viruses are used to get the correct information into
the cell.
What kinds of disorders could be cured this way?
Should we do this? http://www.asgt.org/index.php
Locating Genes
Section 14-3
Gene
Sequence
Promoter
Start
signal
Gene
Stop
signal
Section 14-3
Figure 14-18 DNA Fingerprinting
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.
Go to
Section:
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.
Figure 14-21 Gene Therapy
Section 14-3
Bone
marrow
Normal hemoglobin gene
cell
Chromosomes
Genetically engineered
virus
Nucleus
Bone
marrow