This lesson will increase your knowledge of concepts
covered in the following TEKS for biology:
3.c – Evaluate impact of research on scientific thought, society, and the
environment
3.e – Evaluate models according to their adequacy in representing biological
objects or events
6.c – Identify and illustrate how changes in DNA cause mutations and evaluate
the significance of these changes
6.e – Compare the processes of mitosis and meiosis and their significance to
sexual and asexual reproduction
Previous Lesson
Individuality and
Cloning
Question: What is the
difference between mitosis
and meiosis?
Mitosis is a process producing
body cells whereas meiosis is a
process producing gametes
Daughter cells produced by
mitosis are 2n (diploid) whereas
daughter cells produced by
meiosis are n (haploid)
Question: From a scientific standpoint,
what is the significance of Dolly?
Dolly showed cloning of mammals
was possible
•Scientists can take DNA from an
adult cell and re-start the reading of
the DNA, as if it was DNA in a
fertilized egg
•DNA can then direct the synthesis of
proteins to produce an embryo and
eventually a clone of the adult
Question: From a
chromosomal standpoint,
what is wrong with the idea of
using a sperm and an egg
from super athletes to try to
have a super athlete child?
Random assortment of chromosomes causes the sperm
and egg to have different chromosome combinations
Meiosis I
Meiosis II
Fig. 23.6
Based on: Mader, S., Inquiry Into Life, McGraw-Hill
The child may not get the
“athletic” chromosomes
The chromosomes can line up
223 or 10 million different ways
in meiosis I
Each person can produce 10
million different types of
gametes
Question: Why not try to clone
the super athlete?
Cloning of Humans
• Cloning results in higher rates of
miscarriage and death…using
today’s technology
• Although the clone would be
genetically identical, the environment
that produced the super athlete
would be different…same nature,
different nurture
Today’s Lesson
Genetic Disorders and
Gene Therapy
Overview of Lesson
• Genetic diseases
– Chromosomal
– Single gene
• Genetic Testing
• Gene Therapy
Chromosomal Diseases
• Gametes have abnormal
chromosome numbers and
mutations
• Offspring inherit extra
chromosome or are missing a
chromosome
• Caused by problems with
meiosis
Nondisjunction of chromosomes during meiosis
Based on: Brooks/Cole – Thomson Learning
Characteristics of a child with
Down Syndrome
-wide, rounded face
-mentally retarded
-enlarged tongue
Normal female
karyotype with 46
chromosomes
Based on: Mader, S., Inquiry Into Life, McGraw-Hill
-equal length fingers
-webbed neck
Down syndrome
karyotype with an
extra chromosome 21
Amniocentesis
•Used on pregnant women over 35 years of age
•Performed during weeks 15-17 of pregnancy
•A needle is inserted into the amniotic sac
•Amniotic fluid with fetal cells is removed
•A karyotype of the fetal chromosomes is prepared
Risk of Having Child with Down
Syndrome versus Risk of Miscarriage
due to Amniocentesis
Risk of Down Syndrome
Risk of Miscarriage
Overview of Lesson
• Genetic diseases
– Chromosomal
– Single gene
• Genetic Testing
• Gene Therapy
Important Points about Inheritance
•Genes have different forms, called
alleles
•Each trait is controlled by effects of
two alleles
•Some alleles are dominant/recessive
and other alleles are co-dominant
•Allele for Widow’s Peak
is dominant
•A person with WW or Ww
will have Widow’s Peak
•Allele for Straight Hairline
is recessive
•A person with ww will have
a Straight Hairline
http://images.google.com/
Genotype vs. Phenotype
•Genotype refers to the alleles
•Phenotype refers to the appearance
Example: Genotype - Phenotype
WW - person has a widow’s peak
Ww - person has a widow’s peak
ww - person has a straight hair line
Genetics Problem
• A woman (Ww) with a widow’s
peak has children with a man
(ww) with a straight hairline
• What is the chance that the child
will have a widow’s peak?
Alleles
W = Widow’s peak
w = Straight
Genotypes-Phenotypes
WW - Widow’s peak
Ww - Widow’s peak
ww - Straight
Female
Ww
eggs
W
w
w
Ww
ww
w
Ww
ww
sperm
Male
ww
Each child would
have a 50%
chance of having
a widow’s peak
Question: Why would a person
with a genotype of Ww,
produce gametes with W and
gametes with w?
Gametes
Huntington Disease
Person gradually loses
psychomotor control in
adulthood
Caused by dominant
allele
Genetics Problem
• A woman (hh) with normal
nerve physiology has a child
with a man (Hh) who will
develop Huntington Disease
• What is the chance that the
child will have Huntington
Disease?
Alleles
H = Huntington
h = Normal
Genotypes-Phenotypes
HH - Huntington
Hh - Huntington
hh - normal
Female
hh
eggs
sperm
Male
Hh
Each child would
have a __%
chance of having
Huntington
Disease
Alleles
H = Huntington
h = Normal
Genotypes-Phenotypes
HH - Huntington
Hh - Huntington
hh - normal
Female
hh
eggs
h
h
sperm
Male
Hh
H
Hh
Hh
h
hh
hh
Each child would
have a 50%
chance of having
Huntington
Disease
Cystic Fibrosis
Mucus in bronchi is thick,
interfering with lung function
Caused by a recessive allele
Genetics Problem
• A woman (Nn) with normal lung
physiology has a child with a
man (Nn) who has normal lung
physiology
(both are carriers of allele)
• What is the chance that the child
will have Cystic Fibrosis?
Alleles
N = Normal
n = Cystic Fibrosis
Genotypes-Phenotypes
NN - Normal
Nn - Normal
nn - Cystic Fibrosis
Female
Nn
eggs
sperm
Male
Nn
Each child would
have a __%
chance of having
Cystic Fibrosis
Alleles
N = Normal
n = Cystic Fibrosis
Genotypes-Phenotypes
NN - Normal
Nn - Normal
nn - Cystic Fibrosis
Female
Nn
eggs
N
n
N
NN
Nn
n
Nn
nn
sperm
Male
Nn
Each child would
have a 25%
chance of having
Cystic Fibrosis
Sickle Cell Disease- recessive allele
•Red blood cells are sickle shaped, issues with circulation
causing anemia and pain
Based on: Harvard Family Health Guide, 1999
Genetics Problem
• A woman (Nn) with sickle
cell trait has a child with
a man (NN) who has
normal red cells.
• What is the chance that
the child will have Sickle
Cell Trait?
Alleles
N = Normal
n = Sickle Cell
Genotypes-Phenotypes
NN - Normal
Nn - Sickle Cell Trait
nn - Sickle Cell Anemia
Female
Nn
eggs
sperm
Male
NN
Each child would
have a __%
chance of having
Sickle Cell Trait
Alleles
N = Normal
n = Sickle Cell
Genotypes-Phenotypes
NN - Normal
Nn - Sickle Cell Trait
nn - Sickle Cell Anemia
Female
Nn
eggs
N
n
N
NN
Nn
N
NN
Nn
sperm
Male
NN
Each child would
have a 50%
chance of having
Sickle Cell trait
Overview of Lesson
• Genetic diseases
– Chromosomal
– Single gene
• Genetic Testing
• Gene Therapy
Genetics & Human Diseases
• About 4,000 human diseases are thought
to be inherited
• Scientists are making good progress
figuring out where genes are located on
chromosomes and in understanding how
the mutations in genes cause disease
Genetic map of
chromosome 17
Based on: Mader, S., Inquiry Into Life, McGraw-Hill
Genetic Testing
• Now have DNA tests for 30 - 40
diseases
– Cystic fibrosis, some forms of
breast cancer, fragile X syndrome,
Huntington disease, Duchenne
muscular dystrophy
• Tests are up to 99% accurate
• Tests can be run on embryos
created by in-vitro fertilization prior
to implantation
Future of Genetic Testing
When will we have tests for
1000s of genetic diseases in
human or what project must be
completed for scientists to
understand the DNA-protein
relationships that cause many
human diseases?
Answer
Issues about Genetic Testing
• What if the news is bad? Should the fetus be aborted
or allowed to live with a “cruel” disease?
• Should insurance coverage provide care for a child
having a genetic disease that was diagnosed before
birth?
• Should blood relatives be warned?
• Should our genetics be part of our records?
• Should employers be allowed to consider genetically
based diseases in hiring employees?
• Will eugenics (manipulation of the hereditary qualities
of a race) be practiced?
Overview of Lesson
• Genetic diseases
– Chromosomal
– Single gene
• Genetic Testing
• Gene Therapy
Gene Therapy
• Gene therapy is lagging behind genetic
testing
– For example, gene for cystic fibrosis was
identified in 1989
– Scientists have been testing ways to insert
copies of the normal gene into cells of the
respiratory tract
• It is difficult to get the gene inserted into
the tissue so that it can take over control
of protein synthesis
Steps in Gene Therapy In Utero
Approved gene-therapy trials
Map shows 2004 Stats
•In 2008 938
clinical trials for
gene therapy
ongoing in USA
•In 2008 56 new
trials were
approved in USA
Gene therapy trials are now underway around
the world. When will the results be considered
part of world knowledge?
Next Class
Exam I
(Lessons & Labs)
Genetic tests for 1000s of genetic
diseases will be available after the
Proteome Project is completed…or
after scientists figure out which
proteins go with which
genes…probably in 10-20 years.
Back
Scientific Methodology
Observation
World knowledge in scientific journals
Hypotheses
Publication
Rejection
Tests of hypotheses
Peer review
Results
Submission of paper to scientific
journal
Back
Meiosis - formation of gametes in gonads
Back
Based on: Mader, S., Inquiry Into Life, McGraw-Hill