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Human Heredity
Chapter 14
Human Karyotype

Photograph of cell during
mitosis

Shows if individual got the
right # of chromosomes

Shows homologous
chromosomes paired-up
Number of chromosomes = 46




44 are autosomes
2 are sex chromosomes (XX
or XY)
46, XX (female) or 46, XY
(male)
Sex Determination


Male to female births = 1:1 ratio
Female sex chromosomes – XX

Gametes (egg cells) have one X chromosome


Females - inherit one copy of every gene located
on each of the X chromosomes
Male sex chromosomes - XY

Gametes have either one X or one Y
chromosome

½ carry Y chromosome and ½ carry X
chromosome
Pedigrees

Traces the pattern of inheritance of human
traits through several generations within
families



Must be traits controlled by a single gene
Can determine whether an allele is dominant
or recessive
Used to infer the genotypes of family
members
Pedigree Chart
A circle represents
a female.
A horizontal line connecting
a male and female
represents a marriage.
A half-shaded circle
or square indicates
that a person is a
carrier of the trait.
A completely
shaded circle or
square indicates
that a person
expresses the
trait.
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 neither
expresses the trait
nor is a carrier of
the trait.
Human Genes



Tens of thousands of genes specify characteristics through
proteins
Examples - Blood group genes
ABO blood group – blood type is example of
human trait determined by multiple alleles





IA, IB, i
IA and IB are codominant but both are dominant over i
IA and IB produce A and B antigens on surface of blood
cells
i produces no antigens (ii is type “O”)
Rh blood group – one gene with two allelic forms


Positive allele – Rh+ (dominant)
negative allele – Rh- (recessive)
Figure 14-4 Blood Groups
Section 14-1
Blood Groups
Phenotype
(Blood Type
Genotype
Antigen on
Red Blood Cell
Safe Transfusions
To
From
Recessive Allele Disorder


Must inherit two recessive alleles
(homozygous recessive) to have disorder
PKU – phenylketonuria


Autosomal recessive allele disorder
Inhibits production of enzyme needed to
breakdown phenylalanine


an amino acid found in milk and other foods
Causes build-up of phe. in brain
Autosomal allele disorders

Cystic Fibrosis – Recessive allele disorder
 Causes defect of CFTR protein causes CF
 Caused by Deletion mutation:
 3 bases in gene sequence for CFTR protein is
missing
 Missing codon in mRNA and then a shorter CFTR
polypeptide chain
 Causes the protein called CFTR to fold improperly
and can’t function – leads to absence of CFTR in cell
membranes
 Result is a build up of mucus in the lungs and
digestive tract

An individual is more susceptible to infection and liver
problems
Figure 14-8 The Cause of Cystic Fibrosis
Section 14-1
Cystic Fibrosis
Chromosome
#7
CFTR
gene
The most common allele
that causes cystic fibrosis is
missing 3 DNA bases. As
a result, the amino acid
phenylalanine is missing
from the CFTR protein.
Normal CFTR is a chloride
ion channel in cell
membranes. Abnormal
CFTR cannot be transported
to the cell membrane.
The cells in the person’s airways
are unable to transport chloride
ions. As a result, the airways
become clogged with a thick
mucus.
Sickle Cell Disease

Sickle Cell Disease – Autosomal Codominant
Disorder

RBC’s contain abnormal hemoglobin
Caused by Substitution mutation:

diseased allele differs by one DNA base


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substitutes amino acid valine for glutamic
acid
People heterozygous for sickle cell –
healthy because they have some normal
hemoglobin.
Dominant Allele Disorders

Autosomal dominant allele disorders


Huntington’s Disease – nervous system disorder



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Effects are expressed even when recessive allele is
present (only need one allele for disease)
Progressive loss of muscle control and mental function
No symptoms until thirties or older
Individuals heterozygous for disease – might not pass
allele for disease to offspring
Achondroplasia – form of dwarfism
Autosomal
Disorders
Autosomol
Disorders
caused by
Recessive
alleles
Dominant alleles
Codominant
alleles
include
include
include
Huntington’s
disease
Sickle cell
disease
Galactosemia
Albinism
Cystic
fibrosis
Phenylketonuria
Tay-Sachs
disease
Achondroplasia
Hypercholesterolemia
Sex Linked Disorders


Sex-linked genes are on the sex chromosomes (X or
Y)
 Most are on the X-chromosome
Recessive, sex-linked disorders- more common in males
 Males – have one X so all X-linked alleles are
expressed
 Hemophilia – proteins for blood clotting are missing
 Colorblindness – Inability to distinguish certain
color(s), more common in males because it is a
recessive allele on X chromosome
 Females can have hemophilia and/or
colorblindness
Figure 14-13 Colorblindness
Section 14-2
Colorblindness
Father
(normal vision)
Colorblind
Normal
vision
Male
Female
Daughter
(normal vision)
Son
(normal vision)
Daughter
(carrier)
Son
(colorblind)
Mother
(carrier)
Colorblindness
Father
(normal vision)
Colorblind
Normal
vision
Male
Female
Daughter
(normal vision)
Son
(normal vision)
Daughter
(carrier)
Son
(colorblind)
Mother
(carrier)
25 – both normal vision and red-green colorblind individuals will see this. It is a control test.
45 – a normal individual will see this; red-green color blind individual will see only spots.
29 – a normal individual will see this; red-green color blind individual will see only spots
56 – both normal vision and red-green colorblind individuals will see this.
6 – a normal individual will see this; red-green color blind individual will see only spots.
8 – a normal individual will see this; red-green color blind individual will see only spots.
The individual with normal color vision will see a 5 revealed in the dot pattern.
An individual with Red/Green (the most common) color blindness will see a 2 revealed in the dots
Try to find a circle, a star, and/or a square on this
card in 3 seconds.
Answer: Everyone should be able to see a circle,
star, and square in the demonstration plate
Try to find a circle, a star, and/or a square on this
card in 3 seconds.
Answer: Colorblind individuals should see the
yellow square. Color normal individuals should see
the yellow square and a "faint" brown circle.
Try to find a circle, a star, and/or a square on this
card in 3 seconds.
Answer: Colorblind individuals should see the
yellow circle. Color normal individuals should see
the yellow circle and a "faint" brown square.
Try to find a dog, boat, balloon, or car (as shown in
the above demonstration card) in 3 seconds.
Answer: Colorblind individuals should see nothing.
Color normal individuals should see a "faint" brown
boat.
X-Chromosome Inactivation

Females – One X randomly switched off
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Barr body
Example – calico cats
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Gene for coat color on X chrom.
Possible female genotype: Xorange Xblack
Some parts of body Xorange is turned off and other
parts Xblack is turned off
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Produces mixture of colors in females
Males – single color spots because only have one X
chromosome – Xorange or Xblack
Chromosome Separation
Errors

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Failure of homologous chromosomes to separate during
meiosis (autosomes or sex-chromosomes)
Causes abnormal numbers of chromosomes in gametes
Causes birth defects such as Down Syndrome

Autosomal Trisomy 21 – Mild to severe mental retardation
Homologous
chromosomes
fail to separate
Meiosis I:
Nondisjunction
Meiosis II
Disorders from Nondisjunction
of Sex Chromosome
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If Nondisjunction occurs between sex-chromosomes then
gametes will have the wrong number of sex chromosomes
 Produces Gametes with: 2 X’s, X AND a Y, or NO sex chrom.’s
Role of X chromosome – No human born without an X
chromosome – genes vital for development
Turner’s syndrome (1 in 2500)
 Karyotype 45,X or 45,X0 - female with only one X chromosome
(monosomy X)
 Sterile, various physical characteristics, predominantly affected
by cardiovascular malformations
Klinefelter’s syndrome (1 in 17,000)
 Karyotype 47, XXY – male; sterile
 Language impairment, physical characteristics vary
Human DNA analysis

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Genetic tests used to detect genetic disorders
DNA Probe method
 Hybridize persons DNA – breaks H-bonds between DNA strands
to form single strands
 Mix DNA probes with the persons single DNA strand


Can determine the persons nucleotide sequence depending on
which DNA probes base-pair with the single DNA strand

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DNA probe – known DNA fragments tagged with radioactive markers
Determines if they have the diseased allele mutation
Restriction enzyme Method
 “chemical scissors” – cuts DNA molecules into fragments at
specific DNA sequences
 Detects differences between the lengths of normal and abnormal
alleles
DNA Fingerprinting


Analyzes non-coding sections of DNA (not the genes)
 No two people have exactly the same DNA except for identical
twins
Restriction enzymes -- “cut” DNA into fragments at specific nucleotide
sequences

attracted to Repeats - specific patterns of nitrogen bases

Because the patterns occur in different places the Length of fragments
produced varies from person to person
DNA fragments are analyzed by gel electrophoresis
 Separates DNA fragments by size to produce unique banding
pattern
 bands in each “fingerprint” are analyzed
 If banding patterns in gel are the same then DNA had to come from
the same person

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Everyone has these but not at the same places along the chromosomes
Section 14-3
DNA Fingerprinting
Restriction enzyme
Chromosomes contain large
amounts of DNA called
repeats that do not code for
proteins. This DNA varies
from person to person. Here,
one sample has 12 repeats
between genes A and B,
while the second sample has
9 repeats.
Restriction enzymes are
used to cut the DNA into
fragments containing genes
and repeats. Note that the
repeat fragments from these
two samples are of different
lengths.
The DNA fragments are
separated according to size
using gel electrophoresis. The
fragments containing repeats
are then labeled using
radioactive probes. This
produces a series of bands—
the DNA fingerprint.
Gene Therapy

Used to cure genetic disorders by replacing a
faulty gene with a normal, working gene
 Faulty gene must be identified
 If the gene is successfully replaced and
transcribed by the persons cells the correct
protein or enzyme can be produced
 *Genetically engineered viral DNA – contains
normal, healthy allele of a gene and is injected
into persons bone marrow
Figure 14-21 Gene Therapy
Section 14-3
Bone
marrow cell
Normal hemoglobin gene
Nucleus
Chromosomes
Genetically engineered virus
Bone
marrow
Chapter 14 Quiz I
1. What are the two types of chromosome shown in a Karyotype?
2. True or false: A karyotype can determine if an individual inherited an
incorrect number of chromosomes.
3.In humans a male has how many X chromosomes and how many Y
chromosomes?
4. Human females produce egg cells that have how many X
chromosomes?
5. What percentage of human male gametes carries an X chromosome?
6. A human female inherits how many copies of X-linked genes?
7. What can be used to show how a trait is passed from one generation to
the next within families.
8. True or False: In a pedigree all of the symbols can be squares.
9. Which of the following is determined by multiple alleles?
a. Rh blood group b. ABO blood group c. PKU disease
10. Which of the following genotypes result in the same phenotype?
a. IAIA and IAIB
c. IBIB and IAIB
b. IBIB and IBi
d. IBi and ii
14-1 Quiz Answers
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Autosomes and sex chromosomes
True
One X, and one Y
One
50%
Two
Pedigrees
False
B
B
Chapter 14 Quiz II
1. If a person has PKU which parent did they have to inherit the
recessive allele(s) from?
2. If a man with blood type A and woman with blood type B produce an
offspring, what might be the offspring’s blood type?
3. Sickle cell disease is caused by a change in how many DNA bases?
4. In cystic fibrosis, a change in a single gene causes the CFTR protein
to
A. become less soluble B. fold improperly C. Destroys cell
membranes
5. True or false: A missing codon in the mRNA for the CFTR protein
leads to cystic fibrosis
6. True or False: People heterozygous for sickle cell disease are
healthy because they are resistant to malaria.
7. Most sex-linked genes are on what chromosome?
8. True or False: The allele for colorblindness is located on the Y
chromosome making colorblindness more common in males.
9. True or False: The father of a colorblind boy may be colorblind.
10. Which type of chromosome forms a Barr body?
11. What is the failure of chromosomes to separate during meiosis
called?
12. True or false: A baby can be born without an X chromosome.
13. Which combination of sex chromosomes represents a female?
A. XY B. XXY C. XX D. XXXY
14. If nondisjunction occurs during meiosis, some gametes may
have too few or extra ____________.
15. True or False: Nondisjunction can involve autosomes,
homologous chromosomes, and sex chromosomes.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Both parents
A, B, AB, or O
One
B
True
False
X
False
True
X
11. Nondisjunction
12. False
13. C
14. Chromosome
15. true
Chapter 14 Quiz III
1.
2.
3.
4.
5.
The process of DNA fingerprinting is based on the fact
that no two people, except ______________, have
exactly the same DNA.
True or False: It can be concluded that if two DNA
fingerprints show identical patterns of bands then the
DNA came from two different people.
True or False: the purpose of gene therapy is to cure
genetic disorders.
Which is the first step in gene therapy?
A. identify the faulty gene B. splice normal gene to
viral DNA C. “cut” out the normal gene from DNA
True or False: Gene therapy is successful if the
replacement gene is transcribed in the person’s cells.
6. A person who has ________ is unable to break
down the amino acid Phenylalanine.
7. True of False: A person who has blood type O can
receive a blood transfusion only from a person who
has blood type O.
8. A female with the disorder ____________ inherits
only one X chromosome and has the genotype XO.
9. Nondisjunction in males can lead to the disorder
called ___________________.
10. A boy who has hemophilia inherited the disorder
from his ____________.
Chapter 14 Quiz III
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Identical twins
False
True
A
True
PKU
True
Turner’s
Klinefelters
mother
Chapter 14 Quiz
1.
2.
3.
4.
5.
6.
True or False: Males have two X chromsomes.
True or False: All of the alleles for the ABO blood
group gene are codominant.
A change in just one DNA base for the gene that
codes for the protein _____________ causes
sickle–shaped red blood cells.
What is the dense region in the nucleus that is
formed by the turned-off X chromosome?
True or False: Barr bodies are found only in males.
If you saw a white cat with orange and black spots,
is it most likely a male or a female?
7. The condition in which an individual has three
copies of chromosome is known as
_____________.
8. True or False: Labeled DNA probes can be used to
detect specific sequences found in disease-causing
alleles.
9. What is the method of identification of individuals
that analyzes sections of DNA that have little or no
know function but vary widely from one individual to
another.
10. During what process can an absent or faulty gene
be replaced by a normal working gene?