Transcript Nondisjunction

Chapter 14
The Human Genome
Key Concepts:
 How is sex determined?
 How do small changes in DNA Cause
genetic disorders?
I. Human Chromosomes
A. Karyotype: A picture of chromosomes
taken during mitosis and cut out and
arranged into homologous pairs.
Let us review what we
have previously learned
A Diploid Cell has ________
two sets of homologous
chromosomes. A human diploid cell has ____
46
chromosomes arranged in ____
23 pairs.
Mendelian genetics requires that organisms inherit
____________of
a gene from each parent.
a single copy
In humans, ___________
the gametes (reproductive cells of egg
and sperm) contain a single copy of each gene (one
set of genetic information).
Gametes are formed in the ______
testes (sperm) and
ovaries
__________(egg)
by meiosis.
Each gamete contains 23 chromosomes (one set) or
_______________
haploid number (N) of chromosomes.
Fertilization
____________requires
the egg and the sperm to join
and produce a ______
zygote (fertilized egg) that contains
diploid number (2N).
46 chromosomes (two sets) or _____________
autosomes
Humans have 46 total chromosomes: 44 _________
(body) that follow regular Mendelian genetics, and 2
________________
sex chromosomes (X and Y).
A. A pedigree chart shows the __________
relationship within
a family and can be useful to help with genetic
__________
inheritance problems within families.
B. It is another way to _______
predict an outcome of a
particular cross and the ________
genotype of the family
members.
Figure 14-3 A Pedigree
Section 14-1
Pedigree
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.
Video Notes Worksheet: What are Pedigree Charts?
Video Notes Worksheet:
Pedigree Analyses
Guided Practice
Video Notes Worksheet:
Pedigree Summary
Human Genes
The ______________:
human genome Complete set of genetic
information that is composed of about 30,000 genes.
Human Traits
Phenotypes are determined by __________as
well
genotypes
as ______________
environmentally influenced.
_____________
Environmental influences on gene expression
are not ________,
inherited but genes are.
A trait controlled by a recessive allele
results in a disorder being present
both alleles are present.
only if _____________
• Examples include: PKU
(Phenylketonuria), Tay Sachs, Cystic
Fibrosis, Albinism, and
Galactosemia.
A trait controlled by a dominant allele
results in the disorder being present
one allele is present.
when only ________
• Examples include: Achondroplasia
(dwarfism), Hypercholesterolemia,
and Huntington’s Disease
Autosomal Disorders
Section 14-1
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
Huntington Disease:
It is controlled by a _________________________.
single dominant allele
The gene is located on Chromosome #4.
Genetic degenerative disease that shows no
symptoms until a person is in their
____________________.
It progresses with
thirties or forties
gradual degeneration of their nervous system
leading to loss of muscle control and mental
function until death occurs.
IV. From Gene to Molecule
genetics and phenotype
The link between ______________________
is not easily determined but for several diseases
we have been able to make the connection.
For both ______________
Cystic fibrosis and __________________
Sickle cell disease
single gene
a small change in the DNA of a _____________
structure of a protein causing a
affects the ______________________,
serious genetic disorder.
Codominant Alleles: controlled by
_____________________________.
two alleles that share dominance
• Sickle Cell Anemia is an example.
Sickle Cell Anemia
The patient’s blood cells were found to
be irregularly shaped, like a sickle
_____, and
this is how the disease got its name.
In normal red blood cells
hemoglobin
oxygen
___________carries
_________and
distributes it around the body.
In sickle cell disease, the red blood cells
are sickle–shaped, causing hemoglobin
to no longer carry oxygen as well and
disrupts the normal functioning of cells.
Cystic Fibrosis or “CF” is a common
genetic disease. It is most common in
people of Northern European decent.
Recessive disease a gene found
It is a __________________of
on the # 7 chromosome and affects
digestive and respiratory systems
the__________________________________.
Figure 14-8 The Cause of Cystic Fibrosis
Chromosome
Section 14-1
#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.
The genetics: The allele for sickle cell (HS) is
___________
codominant with the allele for normal
hemoglobin (HA).
Heterozygotes (HS HA) are said to be ____
Sickle____
cell
__________
carriers and have some effects of the disorder
because they have both normal and sickle cell blood
hemoglobin.
DNA normal hemoglobin
CAC GTG GAC TGA GGA CTC CTC
Messenger RNA sequence
GUG CAC CUG ACU CCU GAG GAG
Normal hemoglobin amino acid sequence
Val – His – Leu – Thr – Pro – Glu – Glu…
1
2
3
4
5
6
7 …146
DNA Sickle Cell Anemia
CAC GTG GAC TGA GGA CAC CTC
Messenger RNA sequence
GUG CAC CUG ACU CCU GUG GAG
Val – His – Leu – Thr – Pro – VAL – Glu…
1
2
3
4
5
6
7 …146
The distribution: Sickle Cell anemia is most
prevalent in people of __________________.
African descent
10% of African Americans and 40% of populations
in Africa and Asia carry the gene for Sickle cell
anemia.
Why? The carriers for the disease have a
___________________,
resistance to Malaria a dangerous disease
caused by a blood parasite found in tropical areas of
the world.
Sickle Cell Anemia is a __________
mutation that has
provided an _________
advantage in Malaria prone areas.
In these areas it is _________________________
favored by natural selection
and therefore Sickle Cell Anemia persists in many
heterozygous individuals since the homozygous
recessive condition is lethal. HS
HA
HS
HS HS
HS HA
HA
HS H A
HA HA
Section 14-2: Human Chromosomes
Key concepts: Why are sex-linked disorders more
common in males than in females?
What is nondisjunction, and what problems does it
cause?
A. Sex Determination
1. Female _________
gametescarry an X chromosome
2. _________ gametes can carry either an X or Y (meiosis
segregates
Male the chromosomes; _______ of the sperm
carry X and ______ of the sperm carry Y)
50%
3. In humans, _____________________________ of an
50%
offspring
Female: XX
male: XY
males determine the sex
X
X
XX
Y
XY
X
XX
XY
Sex-linked Genetic Disorders
May be on the X or Y chromosome, but
usually on the X because the Y has very few genes.
males
Most often expressed in ____________because
they only have one X chromosome and thus all the
alleles are expressed even if they are recessive.
Colorblindness is a recessive disorder in which
people can’t distinguish between certain colors.
____________________
colorblindness is most
Red-green
common.
the alleles for normal and
XC and Xc are ___________
colorblind vision.
XC XC and XC Xc are both normal vision females.
carrier for colorblindness and can
XC Xc is a _______________________
pass the gene on to her sons.
Xc Xc is a colorblind female.
XC Y is a normal male and
Xc Y is a colorblind male.
http://www.toledo-bend.com/colorblind/Ishihara.html
Figure 14-13 Colorblindness
Colorblindness
Section 14-2
Father
(normal vision)
Colorblind
Normal
vision
Male
Female
Daughter
(normal vision)
Son
(normal vision)
Daughter
(carrier)
Son
(colorblind)
Mother
(carrier)
Go to
Section:
Figure 14-13 Colorblindness
Colorblindness
Section 14-2
Father
(normal vision)
Colorblind
Normal
vision
Male
Female
Daughter
(normal vision)
Son
(normal vision)
Daughter
(carrier)
Son
(colorblind)
Mother
(carrier)
Go to
Section:
Hemophilia is a __________________________
recessive sex-linked disorder in
which one is unable to clot their blood.
Also known as “bleeders disease”.
Hemophilia is caused by a defect in a gene and the
protein for normal blood clotting is missing.
Figure 21.12
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Slide 16
Royal Family and Hemophilia
Muscular Dystrophy is another
sex-linked recessive disease.
Here the affected individual inherits a degenerative
muscle
__________disorder.
muscle protein is
The gene that codes for a _____________
defective. They rarely live past early adulthood.
replace
Treatments are being explored that ___________
the defective gene.
IV. Chromosomal Disorders
Whole/sets of chromosome mutations
1. _______________
Nondisjunction = failure of homologous
chromosomes to separate normally during
meiosis
This results in a disorder of __________________
chromosome number
2. Examples of disorders include Down’s
Syndrome, Klinefelter’s, and Turner’s
Syndrome
Nondisjunction
Homologous
chromosomes
fail to separate
Meiosis I:
Nondisjunction
Go to
Section:
Meiosis II
Nondisjunction
n+1
n+1
n-1
n-1
chromosome
alignments at
metaphase I
nondisjunction
at anaphase I
alignments at
metaphase II
anaphase II
gametes
Figure 21.19
Page 398
Slide 23
2. Examples of disorders include Down’s
Syndrome, Klinefelter’s, and Turner’s Syndrome
Nondisjunction disorders: Disorders in which
the failure of _____________________
chromosome separationduring
one of the stages of meiosis causes a gamete to
have _______________________________.
too few or too many chromosomes
Nondisjunction can occur in
___________________________.
autosomes or sex chromosomes
Down’s Syndrome: Down’s syndrome is an
example of ____________________________,
nondisjunction of an autosome
specifically chromosome 21.
In Down’s syndrome there is an ___________
extra copy of
chromosome 21 (trisomy 21).
Doing a _____________
karyotype (display of all the
chromosomes in a cell nucleus) and looking at the
chromosomes under a microscope detect the extra
chromosome.
Characteristics of Down’s syndrome include
_________________,
mental retardation physically challenged, facial
irregularities, and often heart defects.
Incidence of Down’s Syndrome and mother’s age
Turners Syndrome: Nondisjunction of the sex
chromosomes in which a chromosome is missing.
45 XO
They have the chromosome makeup of _________
where “O” represents the missing chromosome.
This individual is female in appearance but does not
develop the female sex organs during puberty and is
sterile.
________.
Klinefelter’s Syndrome: Nondisjunction of the sex
extra X chromosome
chromosomes in which an _____________________
is present.
47XXY
They have the chromosome makeup of ________.
male
They are ___________
in appearance and are also
sterile. May also be 48 XXXY or 49 XXXXY
No nondisjunctions of the sex chromosomes have ever
X chromosome
produced and survived without an ______________.
This is because the X chromosome carries many genes
essential for life.
•XXY condition
•Results mainly from nondisjunction in
mother (67%)
•Phenotype is tall males
–Sterile or nearly so
–Feminized traits (sparse facial hair,
somewhat enlarged breasts)
–Treated with testosterone injections
Nondisjunction of Sex Chromosomes
The impact of the sex chromosome
nondisjunction has led us to understand the
Y chromosome in
importance of the ____________
determination of the sex of an individual.
This has recently been determined to be true
because the Y chromosome has been found to
have a gene that turns on __________
male sexual
characteristics in the embryo, even if there
are many X chromosomes present.