The Human Genome

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Chapter 14

• The Human Genome

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14-1 Human Heredity

• I. Karyotype

A. Picture of chromosomes arranged in pairs from
largest to smallest
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II. Human Chromosomes
A. 46 individual or 23 pairs

• 23 from egg and
• 23 from sperm

2. Fertilized egg zygote
B. Pairs 1-22 autosomes
C. Pair 23 sex chromosomes
1. Female
XX
2. Male
XY
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D. Total number of chromosomes are written as
46,XX or 46, XY
E. FemaleMale Ratio 5050
1. Eggs only contain Xs (23,X)
2. Sperm contain an X or a Y (23,X or 23,Y)
III. Pedigree
A. Chart showing the relationship of traits
within a family
B. Uses Symbols

• female

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• male

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A circle representsa female.
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A square represents a male.
A horizontal line connecting a male and a female
represents a marriage.
A vertical line and a bracket connect the parents
to their children.
A circle or square that is not shaded indicates
that a person does not express the trait.
A shaded circle or square indicates that a person
expresses the trait.
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IV. Genes and the Environment
C. Some human traits are almost impossible to
associate with single genes and cant see in a
pedigree
1. Traits, such as the shape of your eyes or
ears, are polygenic
2. Traits only partially genetic ? environment

• A. Some traits phenotypes are strongly influenced
  by environmental, or nongenetic, factors.

B. Example Height
1. Nutritional improvements have increased the
average height by about 10cm
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V. Human Genes
A. Human Genome
1. Contains tens of thousands of genes
2. Human complete set of genetic information
B. Blood Groups
1.Known as ABO blood groups
2. Three Alleles
IA, IB, i
3. IA and IB are codominant
4. Four Blood Types
A, B, AB, and O
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5. Produce antigens on the surface of Red Blood
Cells (RBCs)

• 6. Allele Combinations

A
IAIA, IAi
B
IBIB, IBi
(Universal Recipient)
AB
IAIB
O
ii
(Universal Donor)
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7. Rh blood group
a. determined by a single gene with two alleles
b. Named after the Rhesus Monkey
c. Positive allele (Rh) is dominant (Rh Rh or
Rh Rh-)
d. Negative allele (Rh-) alleles are recessive
(Rh- Rh-)
e. Rh- can give to Rh but Rh cannot give to Rh-
C. Recessive Alleles
1. TWO recessive alleles disorder
(aa)
a. Carriers do not have disorder but carry the
allele for it
(Aa)
Examples Phenylketonuria (PKU), Albinism,
Cystic Fibrosis, Tay-Sachs
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D. Dominant Alleles
1. ONE dominant allele disorder
(HH or Hh)
Examples Huntingtons, Dwarfism
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E. Codominant Alleles
1. Both alleles are dominant both alleles show
in phenotype
2. Example Sickle Cell Anemia
a. Heterozygous for sickle cell
produce both types of RBCs (round and sickle
shaped)
b. Sickle shaped can get stuck in blood vessels
and cause LOTS of pain and block the flow of
blood damaging tissues/organs
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14-2 Human Chromosome

• VI. Human Genes and Chromosomes

A. Smallest human autosomes
1. Chromosomes 21 and 22
a. 21 contains 225 different genes
1. Contains gene for Amyotrophic lateral
sclerosis (ALS)-Lou Gehrigs disease-
degenerative neuromuscular disease
b. 22 contains 545 different genes
1. Contains gene for leukemia and
neurofibromatosis
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B. Sex-Linked Genes
1. Located on sex chromosomes (Pair 23)
2. More than 100 sex-linked disorders on X
chromosome
WHY not Y?
because X is much larger than Y Y only 1 gene
3. Genetic disorders
a. colorblindness, hemophilia, Duchenne Muscular
Dystrophy
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4. Recessive sex-linked alleles more common in
males than females because
a. To be expressed in females, there must be two
copies of the allele, one on each of the two X
chromosomes.
XdXd
b. Males have just one X chromosome. Thus, all
X-linked alleles are expressed in males, even if
they are recessive.
XdY
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VII. Chromosome Inactivation
A. One X is randomly switched off and forms a
Barr Body (This chromosome forms a dense region
in the nucleus )
B. Barr bodies are generally not found in males
because their single X chromosome is still active.
C. Responsible for different color spots in
female cats (Page 352)
1. In parts of the female cat one X is switched
off resulting in black spots and in other parts
of the cat the other X is switched off resulting
in orange spots therefore, orange and black spots
2. Good way to tell male from female males only
have one color spots
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VIII. Chromosomal Disorders
A. The most common error in meiosis occurs when
homologous chromosomes fail to separate
NONDISJUNCTION
B. If nondisjunction occurs, abnormal numbers of
chromosomes enter the gametes, and a disorder of
may result.
Nondisjunction
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C. If two copies of an autosomal chromosome fail
to separate during meiosis, an individual may be
born with three copies of a chromosome.

• Ex Down Syndrome occurs equally in males and
  females
• 47, XX, 21 or 47, XY, 21

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a. Also called Trisomy 21
b. Has three 21 chromosomes
c. produces mild to severe mental retardation
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D. Monosomy
missing a chromosome in a pair
1. Usually do not survive in humans except
Ex. Turner Syndrome 45,XO normal intelligence
female short 3-4 stature sterile b/c never go
through puberty
E. Ploidy entire sets of chromosomes
1. Results from total lack of separation of
homologous chromosomes
Nondisjunction-failure of homologous chromosomes
to separate
a. Gamete inherits a diploid set of chromosomes
i.Triploidy- At fertilization, gamete fuses with
a normal gamete and zygote is triploid.
(3 sets of chromosomes)- banana, apples
ii. Tetraploidy
4 sets of chromosomes (day lily, wheat)
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IX. Sex Chromosome Disorders
A. Disorders that occur on the sex chromosomes
B. In females, nondisjunction can lead to
Turners syndrome.
1. usually inherit only one X chromosome
(karyotype 45,X).
2. Usually are sterile
C. In males, nondisjunction causes Klinefelters
syndrome (karyotype 47,XXY).
1. The extra X chromosome interferes with meiosis
and usually prevents these individuals from
reproducing.
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14-3 Human Molecular Genetics
X. Human DNA Analysis
A. There are roughly 6 billion base pairs in your
DNA.
B. Biologists search the human genome using
sequences of DNA bases
C. DNA testing can pinpoint the exact genetic
basis of a disorder. DNA fingerprinting analyzes
sections of DNA that have little or no known
function but vary widely from one individual to
another.
1. Only identical twins are genetically identical
2. DNA samples can be obtained from blood, sperm,
and hair strands with tissue at the base.
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Letter D is on next slide for guided notes.
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Chromosomes contain large amounts of DNA
called repeats that do not code for proteins.
This DNA pattern varies from person to person.
Restriction enzymes from bacteria are used to
cut the DNA into fragments containing genes and
repeats.
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D. DNA fragments are separated using gel
electrophoresis.
1. This produces a series of bandsthe DNA
fingerprint.
Gel Electrophoresis
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2. Suspect ___
DNA Fingerprint
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XI. The Human Genome Project
A. Attempt to sequence ALL human DNA
B. Completed in June 2000
C. Biotechnology companies are looking for
information that may help develop new drugs and
treatments for diseases.
XII. Gene Therapy
A. an absent or faulty gene is replaced by a
normal, working gene.
B. The body can then make the correct protein or
enzyme, eliminating the cause of the disorder.
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C. Viruses are often used because of their
ability to enter a cells DNA.
D. Virus particles are modified so that they
cannot cause disease.
E. A DNA fragment containing a replacement gene
is spliced to viral DNA.
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F. The patient is then infected with the modified
virus particles, which should carry the gene into
cells to correct genetic defects.
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141

• A chromosome that is not a sex chromosome is know
  as a(an)
• A. autosome.
• B. karyotype.
• C. pedigree.
• D. chromatid.

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141

• Whether a human will be a male or a female is
  determined by which
• A. sex chromosome is in the egg cell.
• B. autosomes are in the egg cell.
• C. sex chromosome is in the sperm cell.
• D. autosomes are in the sperm cell.

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• Mendelian inheritance in humans is typically
  studied by
• A. making inferences from family pedigrees.
• B. carrying out carefully controlled crosses.
• C. observing the phenotypes of individual
  humans.
• D. observing inheritance patterns in other
  animals.

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• An individual with a blood type phenotype of O
  can receive blood from an individual with the
  phenotype
• A. O.
• B. A.
• C. AB.
• D. B.

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141

• The ABO blood group is made up of
• A. two alleles.
• B. three alleles.
• C. identical alleles.
• D. dominant alleles.

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142

• The average human gene consists of how many base
  pairs of DNA?
• A. 3000
• B. 300
• C. 20
• D. 30,000

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142

• Which of the following genotypes indicates an
  individual who is a carrier for colorblindness?
• A. XCX
• B. XCXc
• C. XcY
• D. XCY

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• Colorblindness is much more common in males than
  in females because
• A. the recessive gene on the males single X
  chromosome is expressed.
• B. genes on the Y chromosome make genes on the X
  chromosome more active.
• C. females cannot be colorblind.
• D. colorblindness is dominant in males and
  recessive in females.

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• The presence of a dense region in the nucleus of
  a cell can be used to determine the
• A. sex of an individual.
• B. blood type of an individual.
• C. chromosome number of an individual.
• D. genotype of an individual.

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• Nondisjunction occurs during
• A. meiosis I.
• B. mitosis.
• C. meiosis II.
• D. between meiosis I and II.

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• DNA fingerprinting analyzes sections of DNA that
  have
• A. little or no known function but are identical
  from one individual to another.
• B. little or no known function but vary widely
  from one individual to another.
• C. a function and are identical from one
  individual to another.
• D. a function and are highly variable from one
  individual to another.

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• DNA fingerprinting uses the technique of
• A. gene therapy.
• B. allele analysis.
• C. gel electrophoresis.
• D. gene recombination.

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• Repeats are areas of DNA that
• A. do not code for proteins.
• B. code for proteins.
• C. are identical from person to person.
• D. cause genetic disorders.

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• Data from the human genome project is available
• A. only to those who have sequenced the DNA.
• B. to scientists who are able to understand the
  data.
• C. by permission to anyone who wishes to do
  research.
• D. to anyone with Internet access.

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• Which statement most accurately describes gene
  therapy?
• A. It repairs the defective gene in all cells of
  the body.
• B. It destroys the defective gene in cells where
  it exists.
• C. It replaces absent or defective genes with a
  normal gene.
• D. It promotes DNA repair through the use of
  enzymes.