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Chapter 14
The Human Genome
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
1. 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
D. Total number of chromosomes are written as: 46,XX or 46, XY
E. Female:Male Ratio = 50:50
1. Eggs only contain X’s (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
o = female
 = male
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A horizontal line
connecting a male
and a female
represents a
marriage.
A shaded
circle or
square
indicates
that a
person
expresses
the trait.
A circle
represents
a female.
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
does not express
the trait.
C. Some human traits are almost impossible to associate with
single genes and can’t see in a pedigree
1. Traits, such as the shape of your eyes or ears, are polygenic
2. Traits only partially genetic  environment
IV. Genes and the 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
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
5. Produce antigens on the surface of Red Blood Cells (RBC’s)
6. Allele Combinations:
A
B
AB
O
IAIA, IAi
I BI B, I Bi
IAIB (Universal Recipient)
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 RhC. 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: Huntington’s, 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 RBC’s (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
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 Gehrig’s disease- degenerative neuromuscular
disease
b. 22 contains 545 different genes
1. Contains gene for leukemia and neurofibromatosis
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.
d d
XX
b. Males have just one X
chromosome. Thus, all X-linked
alleles are expressed in males, even
if they are recessive.
d
XY
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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
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.
1. Ex: Down Syndrome; occurs equally in males and females Page 353
47, XX, +21 or 47, XY, +21
a. Also called Trisomy 21
b. Has three #21
chromosomes
c. produces mild to
severe mental retardation
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)
IX. Sex Chromosome Disorders
A. Disorders that occur on the sex chromosomes
B. In females, nondisjunction can lead to Turner’s syndrome.
1. usually inherit only one X chromosome (karyotype 45,X).
2. Usually are sterile
C. In males, nondisjunction causes Klinefelter’s syndrome
(karyotype 47,XXY).
1. The extra X chromosome interferes with meiosis and
usually prevents these individuals from reproducing.
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.
Letter D is on next slide for guided notes.
** Chromosomes contain
large amounts of DNA called
repeats that do not code for
proteins.
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**This DNA pattern
varies from person to
person.
** Restriction enzymes
from bacteria are used to
cut the DNA into fragments
containing genes and
repeats.
D. DNA fragments are
separated using gel
electrophoresis.
1. This produces a
series of bands—the
DNA fingerprint.
Gel Electrophoresis
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2. Suspect ___
DNA Fingerprint
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.
C. Viruses are often used
because of their ability to
enter a cell’s 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.
F. The patient is then infected with the modified virus
particles, which should carry the gene into cells to correct
genetic defects.
14–1
A chromosome that is not a sex chromosome is
know as a(an)
A. autosome.
B. karyotype.
C. pedigree.
D. chromatid.
14–1
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.
14–1
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.
14–1
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.
14–1
The ABO blood group is made up of
A. two alleles.
B. three alleles.
C. identical alleles.
D. dominant alleles.
14–2
The average human gene consists of how many
base pairs of DNA?
A. 3000
B. 300
C. 20
D. 30,000
14–2
Which of the following genotypes indicates an
individual who is a carrier for colorblindness?
A. XCX
B. XCXc
C. XcY
D. XCY
14–2
Colorblindness is much more common in males than in
females because
A. the recessive gene on the male’s 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.
14–2
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.
14–2
Nondisjunction occurs during
A. meiosis I.
B. mitosis.
C. meiosis II.
D. between meiosis I and II.
14–3
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.
14–3
DNA fingerprinting uses the technique of
A. gene therapy.
B. allele analysis.
C. gel electrophoresis.
D. gene recombination.
14–3
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.
14–3
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.
14–3
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.