Name____________________________Date____________________Hour________1
Humans Chromosome 14-2
Intro
 A human ____________________ contains more than ____ billion base pairs of DNA.
 All of this DNA is neatly packed into the _____ chromosomes present in every diploid
human _________
 Genes make up only a ______________ part of chromosomes.
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Human genes and Chromosomes
Chromosomes _____ and _____ are the smallest human _________________
_____________________- body cell
first _______ human chromosomes whose sequences were determined.
Their structural features seem to be representative of other human
____________________.
Chromosome 21
The structure of chromosome _____ is similar to chromosome _____.
It contains about _____________________, including one associated with amyotrophic
lateral sclerosis (ALS)
known as ________________________ disease.
Chromosome 21 also has many regions with no genes at all.
Chromosome 22
Chromosome ______ contains as many as ______ different genes
Genetic disorders on chromosome _____ include:
 an ____________ that causes a form of leukemia
 An allele associated with neurofibromatosis a _____________________ disease of the nervous system.
Chromosome 22 also contains ____________________________ of repetitive DNA that
do not code for proteins.
These sites where rearrangements can occur.
Sex linked genes
Chromosome pair
are the
chromosomes
Genes located on the sex chromosomes are said to be _____________________.
Many sex-linked genes are found on the _____ chromosome.
More than ______ sex-linked genetic disorders have now been mapped to the
______chromosome.
The human ____chromosome is much smaller than the ____ chromosome and appears to
contain only a few genes.
Colorblindness
 _______________ human genes associated with color vision are located on the X
chromosome.
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 In males, a defective version of any one of these genes
produces___________________________
 an inability to
certain colors.
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The most common form of this disorder, red-green colorblindness
 found in about ________________________ males in the United States.
Among females, however, colorblindness is ___________
 only about 1 female in ______________ has colorblindness.
Males have just __________________________.
 All _____________________ alleles are expressed in males, even if they are
_______________________.
In order for a recessive allele, to be expressed in __________________, there must be
_____ copies of the allele, one on each of the two X chromosomes.
This means that the recessive phenotype of a sex-linked genetic disorder tends to be
much more _______________ among males than among females.
In addition, because men pass their _________________________ along to their
daughters, sex-linked genes move from __________________ to their
_________________________ and may then show up in the sons of those daughters.
Hemophilia
______________________ is another example of a sex-linked _____________.
Two important genes carried on the X chromosome help control
__________________________.
A recessive allele in either of these ______ genes may produce a disorder called
hemophilia
In hemophilia, a ______________________ necessary for normal blood clotting is
missing.
About _______________________- males is born with a form of hemophilia.
People with hemophilia can ___________________________ from minor cuts and may
suffer internal bleeding from bumps or _____________________.
Fortunately, hemophilia can be treated by _______________________ of normal
__________________________ proteins, which are now produced using
__________________________________.
Duchenne Muscular Dystrophy
Duchenne muscular dystrophy is a sex-linked disorder that results in the progressive
_______________and loss of ___________________________.
In the United States, 1 out of every ________________ males is born with this
condition.
Duchenne muscular dystrophy is caused by a defective version of the
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__________________________________________for a muscle protein.
Researchers in many laboratories are trying to find a way to treat or cure this disorder,
possibly by ________________________a normal allele into the muscle cells of
Duchenne muscular dystrophy
X inactivation
Females have _____________ X chromosomes, but males have only _____.
If just one X chromosome is enough for cells in males, the cell must
“__________________” to the extra X chromosome in females.
In female cells, one X chromosome is randomly _______________________.
 That turned-off chromosome forms a dense region in the nucleus known as a
_____________________.
 Barr bodies are not found in males because their _________________________is still
active.
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The same process happens in other mammals.
In cats a gene that controls the _________________of coat spots is located on the
_____ chromosome.
 One X chromosome may have an allele for _______________ spots
 the other may have an allele for ___________________ spots.
 one X chromosome is switched off the other X chromosome is switched off.
 The cat's fur will have a mixture of orange and black spots (_____________)
 Male cats have just one X chromosome, can have spots of only_______________.
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Chromosomal Disorders
The most common error in meiosis occurs when homologous chromosomes fail to separate.
This is known as ______________________, which means
“__________________________________.”
If nondisjunction occurs, _________________________ numbers of chromosomes may
find their way into __________________, and a disorder of chromosome numbers may
result.
Down syndrome
If ________________ copies of an ___________________ chromosome fail to
separate during meiosis, an individual may be born with ________________ copies of a
chromosome.
This is known as a ________________, meaning “_____________________.”
The most common form of trisomy involves three copies of chromosome ________ and is
called _________________________________.
In the United States, approximately 1 baby in ____________ is born with Down
syndrome.
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Down syndrome produces mild to severe____________________________.
 also characterized by an increased susceptibility to many diseases
 higher frequency of some __________________________
It is unclear why should an ___________________of _____ chromosome causes so much
trouble.
Researchers know all of the genes on the chromosome, so they can begin experiments to
find the exact genes that cause problems when present in three copies.
Sex Chromosome Disorders
 Disorders also occur among the sex chromosomes.
 Two of these abnormalities are
 __________________
 ___________________.
Turner’s Syndrome
 In females, nondisjunction can lead to Turner's syndrome.
 A female with Turner's syndrome usually inherits only one X chromosome
 (karyotype___________, _________).
 Women with Turner's syndrome are:
 ______________.
 Their sex organs do not develop
 Have ___________________
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Kleinfelter’s syndrome
In males, nondisjunction causes Klinefelter's syndrome
 (karyotype _______, ___________).
The extra X chromosome interferes with meiosis and usually prevents these individuals
from
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Cases of Klinefelter's syndrome have been found in which individuals were
________________or_______________.
There have been no reported instances of babies being born without an ________
chromosome
This indicates that the X chromosome contains genes that are
_____________________________________________and development of an embryo.
The essential role of the Y chromosome is to determine male sex in humans.
The human _____chromosome contains a
_________________________________necessary to produce male sexual
development,
It can do this even if _________________________X chromosomes are present.
If this region of the Y chromosome is absent, the embryo develops as a
_____________________________
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Review
1.Why are sex-linked disorders more common in males than in females?
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2. How does nondisjunction cause chromosome number disorders?
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3.List at least two examples of human sex-linked disorders.
4.Describe two sex chromosome disorders.