Chapter 14 Human Heredity
Human Chromosomes
• A picture of chromosomes arranged in this
way (previous page) is know as a karyotype.
• This karyotype is a typical human body cell.
Its number of chromosomes, 46, helps identify
it.
• Pair # 23 are the sex chromosomes. This
example has 2 X chromosomes, which makes
this person a female.
• The other 22 sets, or 44 chromosomes, are
known as autosomal chromosomes, or
autosomes for short.
• A quick way to write the chromosomes in a
human cell is to put 46XX for a female and
46XY for a male.
Pedigree Charts
• Pedigree charts show the relationships within
a family and can be used to show how traits
are passed from one generation to the next.
Human Genes
• Blood Group Genes:
• The Rh blood group is determined by a single
gene with two alleles: positive and negative.
• Persons with Rh+/Rh+ or Rh+/Rh- are positive.
• Persons with Rh-/Rh- are negative.
• The ABO blood group is more complicated.
• There are three alleles for this gene.
• They are IA, IB, and i. Alleles IA and IB are
codominant.
• These alleles produce molecules called
antigens on the surface of red blood cells.
People with IA and IB alleles produce antigens
for both, making them blood type AB.
• The i allele is recessive. Individuals with IAIA or
IAi produce only the A antigen, making them
blood type A.
• Those with IBIB or IBi are type B.
• Those who are homozygous for the i allele (ii)
produce no antigens and are said to have
blood type O.
Figure 14-4 Blood Groups
Section 14-1
Phenotype
(Blood Type
Genotype
Antigen on
Red Blood Cell
Safe Transfusions
To
From
Recessive Alleles
• Persons that inherit recessive alleles from
their parents sometimes end up with terrible
conditions.
• Albinism: Lack of pigment in skin, hair, eyes.
• Cystic Fibrosis: Excess mucus in lungs.
• Galactosemia: Accumulates sugar in tissues
which causes retardation, eye/liver damage.
• PKU: Accumulates phenylalanine in tissues
which causes retardation.
• Tay-Sachs disease: Lipid accumulation in
brain; causes mental deficiency, blindness,
and death in early childhood.
Concept Map
Section 14-1
Autosomol
Disorders
caused
by
Recessive
Dominant alleles
alleles
include
include
Galactosemia
Albinism
Cystic
fibrosis
Tay-Sachs
disease
Phenylketonuria
Huntington’s
disease
Achondroplas
ia
Codominant
alleles
include
Sickle cell
disease
Hypercholesterolemia
Dominant Alleles
• You only need one allele present to display
these diseases.
• Dwarfism: small body and features.
• Huntington’s disease: Mental deterioration
and uncontrolled movements.
• Hypercholesterolemia: Excess cholesterol
• Codominant Alleles: Sickle Cell disease, which
causes red blood cells to lose shape.
Concept Map
Section 14-1
Autosomol
Disorders
caused
by
Recessive
Dominant alleles
alleles
include
include
Galactosemia
Albinism
Cystic
fibrosis
Tay-Sachs
disease
Phenylketonuria
Huntington’s
disease
Achondroplasia
Codominant
alleles
include
Sickle cell
disease
Hypercholesterolemia
Sex-Linked Genes
• Genes located on the X and Y chromosome
are said to be sex-linked.
• More than 100 genetic disorders have been
found on the X chromosome.
• The Y chromosome is so much smaller and
only has a few genes on it.
• Colorblindness: There are 3 genes associated
with colorblindness on the X chromosome.
• Since males only have one X chromosome, all
X-linked disorders are expressed in males.
Red-green colorblindness is found in 1 out of
10 males in the U.S. while only 1 out of 100
females has colorblindness.
Figure 14-13 Colorblindness
Section 14-2
Father
(normal
vision)
Norm
Colorbli al
Malend
visio
n
Fema
le
Mother
(carrier
)
Daughter
(normal
vision)
Daught
er
(carrier)
Son
(normal
vision)
Son
(colorbli
nd)
• Hemophilia: A disease that keeps blood from
clotting properly.
• Blood clotting is controlled by two genes on
the X chromosome. 1 in 10,000 males is born
with a form of hemophilia.
• Duchenne Muscular Dystrophy: a sex-linked
disorder that results in a progressive
weakening and loss of skeletal muscle.
• In the U.S., 1 out 3000 males is born with this
condition.
• It is caused by a defective version of the gene
that codes for muscle protein.
Chromosomal Disorders
• Nondisjunction: When chromosomes fail to
separate during meiosis.
• This causes abnormal numbers of
chromosomes to find their way into the
gametes, which results in a disorder of
chromosome number.
• Trisomy: Ending up with 3 copies of a
chromosome instead of 2.
• If a person has 3 copies of chromosome 21,
this person has the condition known as Down
Syndrome. This occurs in 1 out of 800 babies
born.
• The main symptoms are mild to moderate
mental retardation.
• Turner’s Syndrome: A female only inherits one
X chromosome (45X).
• These persons are sterile and they cannot
reproduce.
• Klinefelter’s Syndrome: Males get an extra X
chromosome (47XXY).