1. Chapter
14
Human Heredity

2. 14-1 Human Heredity
• Scientists once knew much less about humans then about other “model” organisms
such as fruit flies and mice
• With the completion of the Human Genome Project scientists are on verge of
understanding human genetics at least as well as they understand that of some other
organisms
Human Chromosomes
• To analyze chromosomes, cell biologists photograph cells in mitosis
• Chromosomes are fully condensed and easiest to see during ____________________
Karyotype - _____________________________________________________________
_______________________________________________________________________
• We all began life when a haploid sperm fertilized a haploid egg carrying just
________ chromosomes each.
• The _________________________ zygote or fertilized egg contained the full
complement of __________ chromosomes
Sex chromosomes - _______________________________________________________
_______________________________________________________________________
Females: ___________
Males: _____________
• The regular 44 chromosomes are known as __________________________________
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3. Q: Why are males + females born in a roughly 50:50 ratio?
A: All egg cells carry a single _______ chromosome. However, half of all sperm carry an
_______ chromosome, the other half carry a ________ chromosome
Human Traits
• In order to apply Mendelian genetics to humans, biologists must identify an inherited
trait controlled by a single gene
• Then, they have to study how the trait is passed from one generation to the next
Pedigree - _______________________________________________________________
_______________________________________________________________________
_
3

4. • Most human traits are not coded for by single genes
• Also, many traits are strongly influenced by environmental factors
o Ex.) average height has increased 10cm in the United States and Europe since
1800’s
Polygenic traits - _________________________________________________________
Human Genes
The human genome - ______________________________________________________
• Includes tens of thousands of genes
• Until recently the identification of a human gene took years of work
• Humans aren’t easy test subjects
o
o
o
Blood Group Genes
• A number of genes are responsible for human blood groups, but the best known are
the ABO and Rh blood groups
Rh blood group
Rh is an antigen found in the blood of
• Single gene with two alleles
about 85% of all people; these people are
said to be Rh positive. The rest of the
Rh + (dominant)
population is Rh negative
Rh - (recessive)
Recessive alleles
• Many human genes have become known through the study of genetic disorders
Q: How do scientists identify recessive alleles that cause these disorders?
A:
PKU – phenylketonuria
• Lack enzyme needed to break down phenylalanine
• Found in milk and other foods
• If newborn has PKU, phenylalanine may build up in the tissues during severe mental
retardation
• If newborns are tested early, they can be placed on a low phenylalanine diet which
prevents most of the affects
• PKU is caused by a recessive allele carried on chromosome 12
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5. Tay Sachs
• Autosomal recessive
• Found mostly in Jewish families of central and eastern European ancestry
• Results in nervous system breakdown and death in the first few years of life
• There is no treatment, but there is a test prospective parents can take
Dominant Alleles
• Not all genetic disorders are caused by recessive alleles
Achondropasia – dwarfism
• Never reach 4 feet 4 inches
• Cartilage forms in such a way that the arms and legs end up being disproportionately
short
• 1 in every 10,000 is affected
Huntingtons
• Progressive loss of muscle control and mental function until death occurs
• People with disease show no symptoms until they are in their 30’s and 40’s
Codominant Alleles
• Sickle cell disease
• Affects 1 in 500 African Americans
From Gene to Molecule
Cystic Fibrosis (CF)
• Most common among people whose ancestors come from northern europe
• Caused by a recessive allele on chromosome 7
• Produce a thick heavy mucus that clogs their lungs and breathing passageways
• Serious digestive problems
• Only half survive into their 20’s
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6. Sickle Cell Disease
• Characterized by the bent and twisted shape of the red blood cell
• Sickle shaped red blood cell tend to get stuck in the capillaries
• Produce physical weakness and damage to the brain, heart and spleen
• Sometimes fatal
• Change in _______________________ DNA base
• This change inserts amino acid ______________________ in place of
__________________________________
• Hemoglobin molecules stick together and form long chains that produce the
characteristic shape of sickled cells
Q: Why do so many African Americans carry the sickle cell allele
A: Many African Americans have ____________________________________________
ancestry where _________________________ is a serious problem
• People who are heterozygous for the sickle cell allele don’t get sickle cell and they
don’t get malaria
Malaria and the Sickle
Cell Allele
The map on the left
shows where malaria is
common. The map on
the right shows regions
where people have the
sickle cell allele.
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7. Dominant or Recessive
• It all depends on the nature of a genes protein product and its role in the cell
Ex.) In CF, one copy of the normal allele can supply cells with enough chloride channel
proteins to function therefore the normal CF allele is considered ____________________
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8. Name ____________________________________ Date __________________ Per ____
14-1 Section Review
1. What are sex chromosomes? What determines whether a person is male or female?
2. Using an example, explain how a small change in a person’s DNA can cause a genetic
disorder.
3. How does studying genetic disorders such as PKU help biologists understand normal
alleles?
4. What are some problems biologists face in studying human inheritance?
5. Critical Thinking Predicting If a woman with type O blood and a man with type
AB blood have children, what are the children’s possible genotypes?
14-2 Human Chromosomes
8

9. • A human diploid cell contains more than ____________________________
nucleiotide pairs of DNA
• Despite its size, all of this information is neatly packed into the 46 chromosomes
present in every diploid cell
• Each chromosome is like a library containing hundreds or even thousands of books
• Biologists are many decades away from mastering the contents of these books, but
they are learning just how many books there are and what they deal with
Sex Linked Genes
• Genes located on the sex chromosomes
• Most found on the ________ chromosome
Colorblindness
• Gene associated with color vision are located on the X
chromosome
• Affects 1 in 10 males
• Affects 1 in 100 females
Q: Why the difference between the sexes?
A: Males have ____________________________ X chromosome.
Thus, all X-linked alleles are expressed in males, even if they are
recessive
• In order for a woman to be affected, there must be
__________________________ of the allele
Ex.) What is the probability of a normal vision male and a female
who is a carrier for the color blind trait having a child that is color
blind?
Hemophilia
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10. • A protein necessary for normal ________________________________ is missing
• 1 in 10,000 males
• People with hemophilia can bleed to death from minor cuts and may suffer from
internal bleeding
• Treated with normal clotting factors
Duchenne Muscular Dystrophy
• Results in progressive weaking and loss of skeletal muscle
• Rarely live past early adulthood
• In the U.S. 1 in 3000 males is born with Duchenne muscular dystrophy
• Caused by a defective version of the gene that codes for a muscle protein
X-Chromosome Inactivation
Q: If all you need is one X chromosome, what happens to the extra X chromosome in
females?
A:
• Same in cats, that’s why you can have cats with 3 different colors
o Fur color is on the X chromosome. Some areas have one color switched on,
and others its switched off
Calico Cat: This cat’s fur color is controlled by a gene on the X chromosome.
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11. Chromosomal Disorders
Nondisjunction - __________________________________________________________
_______________________________________________________________________
_
• If nondisjunction occurs, ________________________________________________
_______________________________________________________________________
_______________________________________________________________________
__
Disorders of Chromosome Numbers
Down Syndrome
• When nondisjunction happens and a baby is born with
_________________________ of
__________________________________________
• Trisomy 21
• 1 in 800 in U.S.
• Mild to severe retardation
• Susceptible to many diseases
• Increased frequency of birth defects
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12. Sex Chromosome Disorders
Turners Syndrome (female)
• Only inherit one ___________________________________
• Genotype = ___________
• Women with Turner syndrome are sterile, their sex organs don’t properly develop at
puberty
Klinefelters Syndrome (males)
• Inherit ___________________________________________
• Genotype = ________________
• The extra X interferes with meiosis and usually prevents them from reproducing
• Some cases _______________________________________
• These abnormalities show us the role of Y in sex determination
o Even in combination with several X’s, the Y makes them male
• But if this Y is absent, the
embryo develops into a
female
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13. Name __________________________________ Date __________________ Per ______
14.2 Section Review
1. Why are sex-linked disorders more common in males than in females?
2. How does nondisjunction cause chromosome number disorders?
3. List at least two examples of human sex-linked disorders.
4. Describe two sex chromosome disorders.
5. Critical Thinking Comparing and Contrasting Distinguish between sex-linked
disorders and sex chromosome disorders.
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14. Extra Credit
Animating Nondisjunction
Make a flip book to animate nondisjunction during meiosis. First, make a series of 6
to 10 drawings that gradually show the process of nondisjunction. Then, put the
process in motion by flipping the pages with your thumb.
14.3 Human Molecular Genetics
Human DNA Analysis
• Way too much DNA to search through
• Biologists search the volumes of the human genome using DNA sequences
Testing for Alleles
• If two prospective parents suspect they might be carrying recessive alleles for a
genetic disorder they can now get a test to determine the risk of passing that trait on
to their children
o Use labeled DNA probes to detect specific sequences found in disease causing
alleles
o Looking at changes in restrictive enzyme cutting sites
o Looking at differences in lengths of alleles
DNA Fingerprinting
• Because the human genome is so complex, no individual is exactly like any other
DNA fingerprinting - ______________________________________________________
_______________________________________________________________________
_
_______________________________________________________________________
_
• Used to settle paternity disputes
• Convict criminals and overturn convictions
The Human Genome Project
• Advances in DNA sequencing technologies at the close of the twentieth century made
it possible to begin sequencing entire genomes
• At first, biologists worked on small genomes of viruses and bacteria
14

15. • In 1990, scientists in the United States and other countries began the Human Genome
Project
o An attempt to sequence all human DNA
• In 2000 scientists announced that the DNA sequence of the human genome was
essentially complete
• We estimate as little as 31,000 genes
o Fruit fly – 14,000
o C. elegans worm 20,000
• Now the task is to figure out how so few genes make an organism as complex as us
Searching for genes
Promoter – ______________________________________________________
• Researchers are looking for genes that provide useful clues to some of the basic
properties of life
• Also looking for genetic information that may be useful in developing new drugs and
treatment of disease
A Breakthrough for Everyone
• Data from the human genome project is posted on the internet on a daily basis
• www.genome.gov
Gene Therapy
• The most obvious use of info about the human genome would be to cure genetic
disorders by gene therapy
Gene therapy - ___________________________________________________________
_______________________________________________________________________
_
• Not always been successful, no lasting cure yet
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16. Ethical Issues in Human Genetics
• There are many questions which science will rapidly force society to come to grips
with
• If it’s just as easy to manipulate genes for personal preference then it is to cure a
disease should we do it?
• Our society will have to develop a thoughtful and ethical conscious of what should
and shouldn’t be done with the human genome
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17. Name ____________________________________ Date _________________ Per _____
14-3 Section Review
1. What is the Human Genome Project?
2. Describe how gene therapy works.
3. Name two common uses for DNA testing.
4. Describe how molecular biologists identify genes in sequences of DNA.
5. Critical Thinking Making Judgments Do you think it should be legal for people
to use genetic engineering to affect their children’s characteristics? Give reasons for
your answer.
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18. Chapter 14 The Human Genome
Reviewing Content
Choose the best answer.
1. A normal human diploid zygote contains a full set of
23 chromosomes.
46 chromosomes.
44 chromosomes.
XXY chromosomes.
2. A chart that traces the inheritance of a trait in a family is called a(an)
pedigree.
karyotype.
genome.
autosome.
3. Traits that are caused by the interaction of many genes are said to be
polyploid.
linked.
polygenic.
autosomal.
4. An example of a trait that is determined by multiple alleles is
Huntington’s disease.
ABO blood groups.
Down syndrome.
hemophilia.
5. Most sex-linked genes are found on the
Y chromosome.
O chromosome.
YY chromosomes.
X chromosome.
6. Hemophilia is a genetic disorder that is
sex-linked.
sex-influenced.
fairly common.
more common in women than men.
7. Which parental pair could produce females with colorblindness?
homozygous normal-vision mother, father with colorblindness
mother with colorblindness, normal-vision father
heterozygous normal-vision mother, normal-vision father
heterozygous normal-vision mother, father with colorblindness
8. A common genetic disorder characterized by bent and twisted red blood
cells is
cystic fibrosis.
hemophilia.
sickle cell disease.
muscular dystrophy. 18
9. Which of the following techniques takes advantage of repeated DNA
sequences that do not code for proteins?

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