Name: ______________________ Period: _____
Lesson 7.3: Human Genetics and Biotechnology: Human Chromosomes and Genes
Human Chromosomes and Genes
Key Concept
The human genome consists of at least 20,000 genes on 23 pairs of chromosomes. Of these pairs, 22
are autosomes, and the other pair consists of sex chromosomes (X, Y). Linked genes are located on the
same chromosome; sex-linked genes are located on a sex chromosome. The frequency of crossing-over
between genes is used to construct linkage maps, which show the locations of genes on chromosomes.
Lesson Objective
• Define the human genome.
• Describe human chromosomes and genes.
• Explain linkage and linkage maps.
Chromosomes and Genes
1. How many chromosomes do humans have? _______________________________
2. Which chromosome is the largest? _________________________ the smallest?
_________________
3. How many chromosomes are found in human gametes? _________
4. How many chromosomes are found in human body cells? __________
Autosomes
1. What are autosomes?
______________________________________________________________________________
2. How many autosome pairs do humans have? _____________
Sex Chromosomes
1. What are the human sex chromosomes? ___________________________________
2. What type of sex chromosomes indicate a female? ___________________
3. What type of sex chromosomes indicate a male? ________________
4. What is a Barr body?
______________________________________________________________________________
______________________________________________________________________________
5. How many genes are found on X chromosomes? ______________________________________
6. How many genes are found on Y chromosomes? ______________________________________
7. Which chromosome determines the sex of a developing embryo, the X or the Y? ____________
Human Genes
1. How many genes do humans have? _________________________________________________
2. What percentage of human genes contribute to regulatory elements? __________________
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3. The majority of human genes have two or more possible alleles. Differences in alleles account
for the considerable genetic variation among people. In fact, most human genetic variation is
the result of differences in individual DNA bases within alleles.
Linkage
1. Genes that are located in the same chromosome are called __________________________.
2. Do linked genes segregate together during meiosis? ____________
3. Do linked genes ever get segregated separately during meiosis? _________ If yes, under what
conditions? ____________________________________________________________________
4. The closer together two genes are on a chromosome, the less likely their alleles will be
separated by crossing-over.
5. Why are certain characteristics frequently inherited together?
______________________________________________________________________________
Sex-Linked Genes
1. Genes located on the sex chromosomes are called _______________________________.
2. Why are most sex-linked chromosomes found on the X chromosome?
______________________________________________________________________________
3. What special name is given to sex linked genes found on the X chromosome?
___________________________________________
Mapping Linkage
1. Are genes on non-homologous chromosomes linked? ________Why or why not?
______________________________________________________________________________
2. Genes that are linked on assumed to be found on the same ____________________________
chromosome.
3. What can be used to construct a linkage map? ________________________________________
4. What is a linkage map?
______________________________________________________________________________
5. What can lead to abnormal genetic disorders according to Figure 1.6 in your textbook?
______________________________________________________________________________
Human Inheritance
Key Concept
Traits have different inheritance patterns depending on whether the genes are autosomal or X-linked.
Most human traits have complex modes of inheritance, such as multiple alleles or multiple genes. More
complexity may be introduced by pleiotropy and epistasis. Genetic disorders may be caused by
mutations in one or a few genes or by abnormal numbers of chromosomes.
Lesson Objectives
• Describe inheritance in humans for autosomal and X-linked traits.
• Identify complex modes of human inheritance.
• Describe genetic disorders caused by mutations or abnormal numbers of chromosomes.
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Introduction
1. What kind of characteristics are encoded in DNA? ______________________
Mendelian Inheritance in Humans
1. What does Mendelian inheritance refer to?
______________________________________________________________________________
______________________________________________________________________________
Autosomal Traits
1. What are autosomal traits controlled by? ____________________________________________
2. What does a pedigree chart show you?
______________________________________________________________________________
______________________________________________________________________________
3. What does shading indicate in a pedigree chart? ______________________________________
Sex-Linked Traits
1. What are the two names given to traits controlled by genes on sex chromosomes?
______________________________________________________________________________
2. Where do you find X-linked traits, which sex chromosome? _____________________________
3. Explain who males inherit X chromosomes from and who they can pass it on to.
______________________________________________________________________________
______________________________________________________________________________
4. Do mothers or fathers determine the sex of the offspring? ______________________________
5. What type of X-linked trait is always expressed in males? _______________________________
6. Name two recessive X-linked traits that are common in males but rare in females.
______________________________________________________________________________
7. Why are the traits that you named in question 6 rare in females?
______________________________________________________________________________
______________________________________________________________________________
Pedigree Analysis Activity
1. Ask your instructor for a pedigree analysis activity to complete…
Non-Mendelian Inheritance
1. What is Non-Mendelian inheritance?
______________________________________________________________________________
Multiple Allele Traits
1. What are multiple allele traits?
______________________________________________________________________________
2. What example does your text give you of a multiple allele trait in humans? _________________
3. Stop here… we will watch a video and answer the questions below and fill in the chart.
a. Are ABO blood types inherited in Mendelian Fashion? _______________
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b. What are the four ABO phenotypes? _____________________________________________
c. Complete the chart below as you watch the video:
Phenotypes
Genotypes Antibodies
in the blood
Reaction when blood from groups below is mixed with
antibodies from group at left (PLACE A “C” IN THE
CIRCLES WHERE THE BLOOD WILL CLUMP)
O
O
A
B
AB
A
O
A
B
AB
B
O
A
B
AB
AB
O
A
B
AB
d. What blood type is the universal donor? _____________ Why?
___________________________________________________________________________
___________________________________________________________________________
e. What blood type is the universal acceptor? _______________ Why?
___________________________________________________________________________
___________________________________________________________________________
f. Are Rh antigens inherited in a Mendelian fashion? ____________
Polygenic Traits
1. What do we call human traits that are controlled by more than one gene?
__________________________
2. The alleles of each gene have a minor additive effect on the phenotype. There are many possible
combinations of alleles, especially if each gene has multiple alleles. Therefore, a whole
continuum of phenotypes is possible.
3. What human polygenic trait does the book give you as an example? ____________________
4. What factor other than genetics can affect polygenic traits? __________________________
5. List the two examples from the book given that are caused by the factor in question 5 above.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Pleiotropy & Epistasis
Skip these sections…
Genetic Disorders
1. List two causes of genetic disorders below:
a. ___________________________________________________________________________
b. ___________________________________________________________________________
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Genetic Disorders Caused by Mutations
1. Are most genetic disorders controlled by dominant alleles? ________
2. How does someone become a carrier of a mutant recessive allele?
______________________________________________________________________________
3. Do carriers actually have the disorder? __________
Chromosomal Disorders
1. What is nondisjunction, what happens?
______________________________________________________________________________
______________________________________________________________________________
2. Which chromosome is involved in most chromosomal disorders? _________________________
3. List the four chromosomal disorders found in Table 1.3 that can be caused by nondisjunction.
______________________________________________________________________________
4. What is the genotype for Down’s syndrome? _________________________________________
5. What is the genotype for Turner’s syndrome? ________________________________________
6. What is the genotype for Triple X syndrome (trisomy)? _________________________________
7. What is the genotype for Klinefelter’s syndrome? _____________________________________
8. Which of these syndromes affect females only?
______________________________________________________________________________
9. Which of these syndromes affect males only?
______________________________________________________________________________
Diagnosing Genetic Disorders
1. A genetic disorder that is caused by a ____________________ can be inherited.
2. When should testing for genetic abnormalities be conducted? ___________________________
KQED: Treating Genetic Disorders
1. What is gene therapy?
______________________________________________________________________________
______________________________________________________________________________
Biotechnology
Key Concept
Gene cloning is the process of isolating and making copies of a gene or other DNA segment. The
polymerase chain reaction makes many copies of a DNA segment. Biotechnology can be used to
transform bacteria so they are able to make human proteins. It can also be used to make transgenic
crops that yield more food or resist insect pests. Biotechnology has raised a number of ethical, legal,
and social issues.
Lesson Objectives
• Describe gene cloning and the polymerase chain reaction.
• Explain how DNA technology is applied in medicine and agriculture.
• Identify some of the ethical, legal, and social issues raised by biotechnology.
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Introduction
1. What is biotechnology?
______________________________________________________________________________
______________________________________________________________________________
2. Why are organisms altered using biotechnology?
______________________________________________________________________________
______________________________________________________________________________
Biotechnology Methods
1. What are the two most common techniques used in biotechnology?
______________________________________________________________________________
Gene Cloning
1. What is gene cloning? ___________________________________________________________
2. How is gene cloning used in gene therapy?
______________________________________________________________________________
3. Gene cloning involves four steps: isolation, ligation, transformation, and selection.
a. In isolation, an enzyme is used to break DNA at a specific base sequence. This is done to
isolate a gene.
b. During ligation, the enzyme DNA ligase combines the isolated gene with plasmid DNA from
bacteria. (Plasmid DNA is circular DNA that is not part of a chromosome and can replicate
independently.) The DNA that results is called recombinant DNA.
c. In transformation, the recombinant DNA is inserted into a living cell, usually a bacterial cell.
Changing an organism in this way is also called genetic engineering.
d. Selection involves growing transformed bacteria to make sure they have the recombinant
DNA. This is a necessary step because transformation is not always successful. Only bacteria
that contain the recombinant DNA are selected for further use.
Polymerase Chain Reaction
1. What is polymerase chain reaction?
______________________________________________________________________________
2. What is it used for? _____________________________________________________________
3. PCR involves three steps: denaturing, annealing, and extension. They are repeated many times
in a cycle to make large quantities of the gene.
a. Denaturing involves heating DNA to break the bonds holding together the two DNA strands.
This yields two single strands of DNA.
b. Annealing involves cooling the single strands of DNA and mixing them with short DNA
segments called primers. Primers have base sequences that are complementary to segments
of the single DNA strands. As a result, bonds form between the DNA strands and primers.
c. Extension occurs when an enzyme (Taq polymerase or Taq DNA polymerase) adds
nucleotides to the primers. This produces new DNA molecules, each incorporating one of the
original DNA strands.
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Applications of Biotechnology
1. What two fields utilize biotechnology? ______________________________________________
Applications in Medicine
In addition to gene therapy for genetic disorders, biotechnology can be used to transform
bacteria so they are able to make human proteins. Proteins made by the bacteria are injected into
people who cannot produce them because of mutations. Insulin was the first human protein to be
produced in this way.
KQED: Pharmacogenomics & KQED: Synthetic Biology
Skip these sections…
Applications in Agriculture
1. What are transgenic crops?
______________________________________________________________________________
Ethical, Legal, and Social Issues
The use of biotechnology has raised a number of ethical, legal, and social issues. Here are just a few:
• Who owns genetically modified organisms such as bacteria? Can such organisms be patented like
inventions?
• Are genetically modified foods safe to eat? Might they have unknown harmful effects on the people
who consume them?
• Are genetically engineered crops safe for the environment? Might they harm other organisms or
even entire ecosystems?
• Who controls a person’s genetic information? What safeguards ensure that the information is kept
private?
• How far should we go to ensure that children are free of mutations? Should a pregnancy be ended if
the fetus has a mutation for a serious genetic disorder?
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