Name _____________________________________________________________
Test Date _Tues, 2/15___
UNIT 11 – THE HUMAN GENOME
I. HUMAN GENETICS
(pp. 341-343)
A. Human Somatic Cells
Human somatic cells (_body__ cells) are _diploid___ or _2n___. Each cell contains _46___ chromosomes, or
_23___ pairs of chromosomes. Of these pairs of chromosomes, _22___ pairs are _homologous____ pairs, meaning
they contain the same genes in the same order. The 44 chromosomes that make up the 22 homologous pairs in
each cell are called _autosomes_______. The 23rd pair of chromosomes are the _sex___ chromosomes. In female
somatic cells, the sex chromosomes are _XX___; in a male’s cells, the sex chromosomes are _XY___.
B. Human Gametes
Gametes are _haploid___, or _n__, and contain _23___ chromosomes. Female gametes are _egg__ cells and male
gametes are _sperm___cells. Gametes are produced through the process of _meiosis______ in the _ovaries_____
or _testes______, respectively. In meiosis, when the _homologous______ pairs of chromosomes separate in
_anaphase I____, the sex chromosomes separate also. The resulting egg cell can only contain an _X___
chromosome, while the sperm cell produced has a _50__% chance of containing a __Y___ and a _50__% chance of
containing an _X___. Therefore, the _male___ determines the sex of the offspring.
C. Analyzing Human Chromosome Numbers
1. Nondisjunction - Abnormal numbers of chromosomes in _gametes________ result in genetic disorders called
_number disorders_____. This must often is a result of _nondisjunction___, which means _”not coming apart”___.
In nondisjunction, a chromosome pair fails to separate correctly in _anaphase______ so the
gametes produced have an abnormal _number of chromosomes______. Number disorders are not
inherited; therefore, they cannot be predicted with _Punnett squares_________.
2. Karyotypes - A karyotype is a photograph of _chromosome pairs_______.
Cells from the developing embryo or individual being tested are cultured in a nutrient growth medium, then
chemically treated to stop _mitosis_______. The cells are stained, the chromosomes photographed, and
the photograph is enlarged. The chromosomes are cut out and arranged in _homologous ___ pairs in size order,
with the _sex____ chromosomes making up the 23rd pair. Karyotypes can only be used to detect _number______
disorders and to determine the _gender__ of an unborn child. They do not detect abnormal _genes_______;
therefore, a normal karyotype does not guarantee a _normal______ child!
II. HUMAN GENETIC DISORDERS – NUMBER DISORDERS
(pp. 352, 353)
A. Autosomal Number Disorders
Most autosomal number disorders are _lethal____. The only autosomal number disorder that allows
survival into adulthood is _Down syndrome____.
Down syndrome is also known as _trisomy 21_______ because there are _3______ chromosomes at
the __21st_____ position, instead of _2___. Individuals have characteristic facial features; growth, behavior,
and mental development are all affected. There is also a higher risk of _congenital____ heart defects. The
incidence of babies with Down syndrome is much higher in _older__ mothers.
B. Sex Chromosome Number Disorders
1. Turner Syndrome
Also called _45 X0______ because individuals lack _2nd sex chromosome_____. Patients are
_female____, typically _short____ in stature, underdeveloped sexually, _sterile______, with a
normal life expectancy.
2. Klinefelter Syndrome
Also called _47 XXY___. Symptoms do not appear until _puberty_ at which time affected _males____
show poor sexual development and infertility. Treated with _testosterone___. Normal life expectancy.
III. ANALYSIS OF HUMAN INHERITANCE
A. Punnett Squares & Multiple Alleles (pp. 345-346)
Most genes follow Mendel’s basic principles of 2 alleles in which one is dominant and the other, recessive.
There are some genes that have multiple alleles; that is, _more than 2____ alleles. An example
of this is ABO blood groups. There are _3____ alleles for this gene. Two of the alleles, _A__
and __B____ are co-dominant, meaning __they always show ________ if
present. The third allele, __o______, is recessive, meaning it will only show if the genotype is _oo______.
Each individual inherits __2___ alleles for this gene, one from __mom____ and one from __dad_____.
The possibilities for blood group genotypes and phenotypes are:
Phenotype
Type A blood
Genotype
Type B blood
Type AB blood
Type O blood
1. A couple preparing for marriage have their blood typed. Both are AB. They ask you what types of
blood their children may have. What would you tell them?
Cross: __________________________________
Phenotype Ratio: ________________________________________
2. An old, rich couple die in an accident. Soon a man shows up to claim their fortune, saying he is the
long-lost son who ran away with a circus as a boy. Other relatives say he is lying. Hospital records
show the couple'’ blood types were AB and O. The claimant is O.
Cross: __________________________________
Is he an imposter? _______________
B. Pedigrees
A pedigree is a diagram that follows the inheritance of a single _trait___ through several _generations__
of a family. In a pedigree, males are represented by _squares____ and females, by _circles____.
Individuals with the trait are represented with _shaded____ figures. Individuals shown with unshaded figures
_do not show the trait___. Vertical lines connect _parents____ and _children____. Horizontal
lines connect _spouses___ or _siblings__. Children are placed in _birth order__, from _left___ to
_right_____.
1. The following pedigree shows the inheritance of a recessive trait.
a.
b.
c.
d.
e.
How many generations are shown in this pedigree? _______________
How many children did Parents I1 and I2 have? ________ How many boys? _______ Girls? ________
How many children did Parents II1 and II2 have? ________ How many boys? _______ Girls? ________
Key: _______________________________________________________________________
To solve a pedigree: Label all ________________________________________________ first!
2. Determine the genotype of all individuals in this pedigree showing the inheritance of red hair, a recessive
trait.
Key: ___________________________________________________________________
3. Determine the genotype of all individuals in the following pedigree showing the inheritance of a dominant
trait.
Key: __________________________________________________________________
IV. INHERITED HUMAN GENETIC DISORDERS
A. Gene Mutations
Inherited human genetic disorders are the result of gene mutations; that is, _a change in the DNA sequence of the
gene________.
B. Types of Inherited Genetic Disorders
1. Sex-Linked Disorders – Mutated gene is on the _X__ chromosome.
2. Autosomal Genetic Disorders – Gene mutation is on any chromosome other than _sex chromosomes____
V. GENETIC DISORDERS - SEX-LINKED DISORDERS
A. Sex-Linked Inheritance (pp.350, 351)
A gene is referred to as “sex-linked” if it is located on a sex chromosome (_X__ or _Y__). In humans,
sex-linked genes are almost always located on the larger _X___ chromosome. The _Y__ chromosome is
much smaller and carries only a few genes related to _sexual development_____. Females have __2__ X
chromosomes; males have _one____. Females will only show recessive traits located on the X chromosome if
they are _homozygous recessive________. But a male will always show a recessive trait located on the
X chromosome because he only has _one__ X chromosome, so all _genes___ on the X chromosome will show.
This results in _males___ having a much higher incidence of sex-linked disorders.
1. Genotypes for sex-linked traits are written using the X and Y chromosomes to show path of inheritance. For
example, male-pattern baldness is a sex-linked recessive trait. If H = normal head of hair and h = baldness,
bald male = _Xh Y_____; bald female = _ Xh Xh ___. Females can be __carriers___ for sex-linked
recessive disorders. A carrier has the defective allele, but _it does not show___________. The
genotype of a female carrier is _XH Xh _____. Males _cannot_____ be carriers for sex-linked
traits because their 2nd sex chromosome is the _naked Y___!
2. Sex-Linked Punnett Squares – In sex-linked traits, probabilities for male and female offspring must be
calculated separately because traits are _inherited differently___.
If a man with a full head of hair marries a woman who is heterozygous, what is the probability they would have a
son who would go bald? A daughter?
Key: ______________________________________
Cross: _____________________________________
Probability of bald daughter = ___________
Probability of bald son = ____________________
B. Sex-Linked Disorders – All of these disorders are sex-linked _recessive_____.
1. Color Blindness – Inability to differentiate and distinguish _colors_____.
2. Hemophilia – Missing an enzyme required for normal _blood clotting_____ - results in
_uncontrolled bleeding________. Treated with blood transfusions, injections of missing factor.
3. Duchenne’s Muscular Dystrophy – Symptoms develop at _3 – 6 years______. Muscles
_weaken, break down________________, leading to eventual death. No available _treatment____ or
_cure_____. Death usually occurs before adulthood.
C. Examples
1. A colorblind female marries a man with normal vision. What is the probability of colorblind children?
Key: ______________________________________
Cross: _____________________________________
Probability of colorblind daughter = ____________ Probability of colorblind son = ____________
2. A genetics counselor interviews a couple with a family history of hemophilia to evaluate the possibility
of offspring with the disorder. The woman does not have hemophilia, but states that her father had
the disorder. The man is normal.
Key: ___________________________________________
Cross: ___________________________________
Probability of daughter with hemophilia = ___________
Probability of son with hemophilia = __________
3. The following pedigree shows the path of inheritance of hemophilia through several generations. Identify the
genotypes of each individual.
Key: ________________________________________________________________
VI. GENETIC DISORDERS - AUTOSOMAL DISORDERS
(pp. 345-348)
Most genes are carried on the _autosomes_______, _44___ chromosomes other than the sex
chromosomes. So it follows that most genetic disorders are _autosomal___ disorders. These disorders
affect males and females _equally_____ and are due to _gene___ mutations. Autosomal disorders
can be divided into three groups based on the pattern of inheritance.
A. Autosomal Recessive Disorders
1. Albinism – Characterized by failure to produce pigment, _melanin___. Affected individuals lack
coloration in _eyes__, _skin___, and _hair___. Very susceptible to _UV light____.
Symptoms appear _at birth_____; _Normal______ life expectancy.
2. Tay-Sachs Disease – Characterized by inability of _brain___ cells to break down a specific type of
_lipid___. Symptoms appear _soon after birth____. Lipid build-up causes seizures,
blindness, degeneration of mental & motor skills, and death at _2 – 4 years__. Historically associated
with _Jewish____ population, although genetic _testing_____ has decreased its incidence.
3. Cystic Fibrosis – Characterized by excess _mucus production______ in _lungs________,
__digestive___ system. Symptoms appear just after birth and include frequent respiratory
infections, poor nutrition. With treatment, patients can survive to young adulthood. Cystic fibrosis is
the most common _fatal__ genetic disorder in the _United States___ among Caucasians.
4. Phenylketonuria or _PKU___ - Characterized by an inability to breakdown the amino acid,
_phenylalanine___. Build-up results in severe mental retardation. All babies born in US
hospitals are tested for PKU because it is easily treated with a diet low in _protein_____.
B. Autosomal Co-Dominant Disorders
Sickle cell anemia is an autosomal co-dominant disorder that affects _hemoglobin___ production.
Hemoglobin is the protein that binds _oxygen____ to red blood cells.
1. Individuals with the normal genotype, AA, do not have the sickle cell allele and produce only normal
hemoglobin.
2. Individuals that are SS produce abnormal hemoglobin that causes the red blood cells to “sickle” when
oxygen availability is decreased; for example, in high altitudes or during periods of stress. Sickled
RBCs are more fragile, easily destroyed – results in lack of _energy____ due to decreased
_ATP____ production in cells, blockage of blood vessels, and severe pain. Shortened life
expectancy. Most common inherited disease in individuals of _African_ ancestry.
3. Heterozygotes (AS) produce both normal and abnormal hemoglobin and are said to have
_sickle cell trait___. They do not show symptoms of the disorder. In certain areas, individuals with sickle cell
trait have a benefit over individuals that lack the sickle cell allele because they are resistant to
_malaria____. Malaria is a serious, sometimes fatal disease spread by _mosquitoes___ that affects millions of
people each year in _Africa__. This increased malarial resistance has resulted in a very high incidence of AS
individuals. If two heterozygotes marry and have children, they have a _25__% chance of having a child with
sickle cell anemia.
C. Autosomal Dominant Disorders
1. Marfan Syndrome – Dominant disorder that affects the _connective______ tissue of the
_skeletal___ system, eyes, and _circulatory_____ system. Affected individuals have very long
limbs, vision problems, and are susceptible to _aortic____ rupture.
2. Huntington’s Disease – Fatal genetic disorder in which symptoms do not show until _30s to 40s___.
Characterized by deterioration of _nervous system_____.
3. Achondroplasia - _Dwarfism___