Download Human Inheritance

Name ______________________________________________________________________
Test Date _Block Day, 2/15 or 2/16_
UNIT 9 – 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 _X__ and a _50__% chance of containing an _Y___. 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 most often is a result of _nondisjunction________, which means
_”not coming apart”_____. Nondisjunction may occur in:
 _Anaphase I___ if _homologous pairs_________ do not separate correctly
 _Anaphase II___ if _sister chromatids_________ do not separate correctly
In either case, _gametes____ are produced with an abnormal number of chromosomes.
2. Karyotypes - A karyotype is a photograph of _chromosome pairs______.
Cells from the developing embryo or individual being tested are cultured, and treated to stop _mitosis______ in
_metaphase_____. 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______.


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. Higher risk of
_congenital___ heart defects.
Incidence of babies with Down syndrome is much higher in _older____ mothers.

B. Sex Chromosome Number Disorders
1. Turner Syndrome


Also called _45XO______ because individuals lack _2nd sex chromosome__.
Affected individuals are _female_____, typically short in stature, underdeveloped sexually, with a normal life
expectancy.
2. Klinefelter Syndrome


Also called _47XXY____________.
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)
A multiple alleles gene has _more than 2___ possible alleles. An example of this is ABO blood groups. There are
_3___ alleles for this gene.
 _I A (A)___ and _I B (B)______ are co-dominant, meaning _they show ______ if present.
 _i (o)_______ is recessive, meaning it will only show if the genotype is _ii (oo)______.
The possibilities for blood group genotypes and phenotypes are:
Phenotype
Type A blood
Genotype
AA, Ao
Type B blood
BB, Bo
Type AB blood
AB
Type O blood
oo
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.
 Males are represented by _squares_____ and females, by _circles_____.
 Individuals with the trait are represented with _shaded____ figures.
 Vertical lines connect _parents____ and _children____. Horizontal lines connect _spouses_____ or _siblings_____.
 Children are placed in _birth order______, from _oldest____ to _youngest_____.
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 _puberty____. 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.
 Male-pattern baldness is a sex-linked recessive trait. If H = normal head of hair and h = baldness,
o Bald male = _X h Y______
o Bald female = _X h X h____
 Females can be _carriers_____ for sex-linked recessive disorders. A carrier has the defective allele, but _it doesn’t
show______.
o The genotype of a female carrier is _X H X h______.
o Males _cannot__ be carriers for sex-linked traits because their 2nd sex chromosome is the
_”naked Y”__!
2. Sex-Linked Punnett Squares
A man with a full head of hair marries a woman who is heterozygous. If they have a son, 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 _red/green__________________.
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
 Muscles gradually weaken 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)
More common that sex-linked disorders because _there are 44 autosomes compared to 2 sex chromosomes__. These disorders
affect males and females _equally__ . 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____.
 Very susceptible to _UV light____.
2. 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 into adulthood.
 Most common _fatal___ genetic disorder in the _United States____ among Caucasians.
3. Phenylketonuria or _PKU___
 Characterized by an inability to breakdown the amino acid, _phenylalanine_____.
 If untreated, 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. AA
 Individuals with the normal genotype do not have the sickle cell allele and produce only normal hemoglobin.
2. SS
 Sickle Cell Anemia
 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. AS
 Described as _sickle cell trait____________
 Produce both normal and abnormal hemoglobin
 Do not typically show symptoms of the disorder.
 Heterozygote Advantage – Provides resistance to _malaria_____.
C. Autosomal Dominant Disorders
1. Huntington’s Disease
 Fatal genetic disorder in which symptoms do not show until _mid 30s or 40s___.
 Characterized by deterioration of _nervous system____.
2. Achondroplasia - _Dwarfism___