Pedigree
Section 14-1
Pedigree – a graphic representation of genetic inheritance
Circle – usually represents a female
Square – usually represents a male
Shaded circles and squares – represent individuals showing the trait
being studied
Unshaded – do not show the trait
Half-shaded circles and squares represent a carrier.
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Section:
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.
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Section:
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.
Pedigree Activity
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Section:
Karyotype
Karyotype – chart of chromosome pairs that may be
used to determine a genetic disorder.
Homologous- matching chromosomes
Autosomes- chromosomes that are not sex
chromosomes; normally humans have 22 pair
Sex Chromosomes – the 23rd pair of chromosomes;
females have a matching set of homologous
chromosomes (XX), males do not (XY)
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Section:
Karyotype Picture
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Section:
Interest Grabber
Section 14-2
Gender Benders
You may remember that in humans, the sperm cells may carry an X
chromosome or a Y chromosome, while egg cells have only X
chromosomes. Sometimes, errors during meiosis in one of the parents
produce offspring with an abnormal number of sex chromosomes.
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Section:
Disorders
Nondisjunction
Changes in Chromosome Numbers
Nondisjunction – failure of chromosomes to separate properly
during the process of meiosis
Down Syndrome (Trisomy 21) – extra 21st chromosome
Turner Syndrome – individual is missing a sex chromosome 45XO
Klinefelter Syndrome – individual has an extra X chromosome 47
XXY
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Section:
Disorders
Codominance in Humans
Sickle Cell Anemia – affects black Americans whose
families originated in Africa and in white Americans whose
families originated in the countries surrounding the
Mediterranean Sea. An individual who is homozygous for
sickle cell will suffer from the disease. If the person is
heterozygous, they only carry the disease. They are
codominant for the disease. In sickle cell the protein
hemoglobin differs by one amino acid. This defective
hemoglobin forms crystal-like structures that change the
shape of the red blood cells.
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Section:
Sickle Cell
Picture of a sickle cell
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Section:
Genetic Disorders
Tay-Sachs disease -recessive disorder of the central
nervous system; affects individuals of Jewish descent.
Phenylketonuria (PKU)-a recessive disorder that results
from the absence of an enzyme that converts one
amino acid to a different amino acid.
Cystic fibrosis -common genetic disorder among white
Americans. It is due to a defective protein in the plasma
membrane. CF results in the formation and
accumulation of thick mucus in the lungs and digestive
tract.
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Section:
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.
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Section:
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.
Sex-Linked Traits in Humans
Red – green color blindness – cannot differentiate
between red and green.
XCY – normal
XcY – colorblind
XCXC – normal
XCXc – normal
XcXc – colorblind
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Section:
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Section:
Figure 14-13 Colorblindness
Section 14-2
Father
(normal vision)
Colorblind
Normal
vision
Male
Female
Daughter
(normal vision)
Son
(normal vision)
Daughter
(carrier)
Son
(colorblind)
Mother
(carrier)
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Section:
Sex Linked Traits in Humans
Hemophilia – X-linked disorder that causes a problem
with blood clotting.
XHY – normal
XhY – hemophilia
XHXH – normal
XHXh – normal
XhXh – hemophilia
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Section:
Multiple Alleles in Humans
ABO blood groups are determined by multiple alleles.
Type A – contains A antigens (alleles)
Type B – contains B antigens
Type AB – contains both A and B
Type O – has neither A nor B
Table 12.3 page 331
Rh antigen – positive has the antigen
Negative does not.
O – universal blood donor
AB – universal blood recipient
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Section:
Interest Grabber
Section 14-3
Bioethics and You
As you become more aware of scientific advances in genetics, you might
realize that with the ability to manipulate genes, there comes responsibility.
This ability provides an opportunity to improve the lives of many people.
But there is also a potential for errors or intentional misuse of the
technology.
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Section:
Interest Grabber continued
Section 14-3
Working with a partner, answer the following questions.
1. In what type of situation do you think genetic engineering—changing
the genes of organisms—is warranted? Explain your reasoning about
your position. If you do not think that genetic engineering is ever
warranted, explain your reasons for your position.
2. In what type of situation do you think genetic engineering might be
misused? Suggest limits that might be placed on the manipulation of
genes to avoid its misuse.
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Section:
Videos
Click a hyperlink to choose a video.
Human Sex Determination
Nondisjunction
Point Mutation
Video 1
Human Sex Determination
Click the image to play the video segment.
Video 2
Nondisjunction
Click the image to play the video segment.
Video 3
Point Mutations
Click the image to play the video segment.
Go Online
Links from the authors on DNA samples
Career links on geneticists
More information on the Human Genome Project
Interactive test
For links on pedigrees, go to www.SciLinks.org and enter the Web
Code as follows: cbn-4141.
Interest Grabber Answers
1. This pedigree shows the inheritance of attached ear lobes. Which parent
has attached ear lobes?
The father
2. How many children do the parents have? Which child has attached ear
lobes?
Three; the daughter has attached ear lobes.
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?
The second son; no; yes, the daughter
Interest Grabber Answers
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?
One half of the offspring will be males; the other half, 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?
One of the gametes has two X chromosomes instead of just one. This might
have resulted from a mistake in meiosis: Instead of separating, the pair of X
chromosomes stayed together.
3. How do the offspring in the two Punnett squares differ?
Instead of two XX and two XY offspring, there are one XX and one XY (which
are normal), plus one XXX and one XXY (which are abnormal).
Interest Grabber Answers
1. In what type of situation do you think genetic engineering—changing the
genes of organisms—is warranted? Explain your reasoning about your
position. If you do not think that genetic engineering is ever warranted,
explain your reasons for your position.
Students’ answers likely will include medicinal uses of genetic engineering,
such as gene therapy for genetic diseases and production of needed
substances such as insulin. Some students may object to all genetic
manipulations.
2. In what type of situation do you think genetic engineering might be
misused? Suggest limits that might be placed on the manipulation of genes
to avoid its misuse.
Students’ answers may include the “designing” of human babies with
desirable traits and the cloning of humans. Some students may object to
genetically altered foods.
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