Transcript Standard 3—Genetics

Standard 3—Genetics
Mendel’s Law
3. A multi-cellular organism
develops from a single zygote,
and its phenotype depends on its
genotype, which is established at
fertilization.
3a. Know how to predict the
probable outcome of phenotypes
in a genetic cross from the
genotypes of the parents and
mode of inheritance (autosomal
or X-linked, dominant or
recessive.
Sex-Linked Genes
Sex-Linked Genes
The ___ chromosome and the __
chromosomes determine sex.
Genes located on these chromosomes are
called ________________ genes.
More than ____ sex-linked genetic disorders
have now been mapped to the X
chromosome.
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Sex-Linked Genes
X Chromosome
Duchenne muscular
dystrophy
Melanoma
The __ chromosome
is much smaller than
the __ chromosome
and appears to
contain only a few
genes.
X-inactivation center
X-linked severe combined
immunodeficiency (SCID)
Colorblindness
Hemophilia
Y Chromosome
Testis-determining
factor
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Sex-Linked Genes
Why are sex-linked disorders more common in males
than in females?
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Sex-Linked Genes
For a __________ allele to be expressed in
females, there must be two copies of the allele,
one on each of the two X chromosomes.
Males have just ______ X chromosome. Thus, all Xlinked alleles are expressed in males, even if they are
recessive.
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Sex-Linked Genes
Colorblindness
Three human genes associated
with color vision are located on
the ______ chromosome.
In males, a defective version of
any one of these genes
produces ________________.
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Sex-Linked Genes
Possible
Inheritance of
Colorblindness
Allele
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Sex-Linked Genes
Hemophilia
The ___ ______________ also carries genes
that help control blood clotting. A recessive
allele in either of these two genes may
produce hemophilia.
In ______________, a protein necessary for
normal blood clotting is missing.
Hemophiliacs can bleed to death from cuts and
may suffer internal bleeding if bruised.
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Sex-Linked Genes
Duchenne Muscular Dystrophy
Duchenne muscular dystrophy is a
_______________ disorder that results in the
weakening and loss of skeletal muscle.
It is caused by a defective version of the gene
that codes for a muscle protein.
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X-Chromosome Inactivation
X-Chromosome Inactivation
British geneticist Mary Lyon discovered that in
female cells, one ___ chromosome is
randomly switched off.
This chromosome forms a dense region in the
nucleus known as a Barr body.
Barr bodies are generally not found in males
because their single ___ chromosome is still
active.
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Chromosomal Disorders
Chromosomal Disorders
What problems does nondisjunction cause?
The most common error in meiosis occurs when
homologous chromosomes fail to separate.
This is known as ________________, which means,
“not coming apart.”
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Chromosomal Disorders
Nondisjunction
Homologous
chromosomes
fail to separate.
Meiosis I:
Nondisjunction
Meiosis II
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Chromosomal Disorders
Down Syndrome
If ______ copies of an autosomal chromosome
fail to separate during meiosis, an individual
may be born with three copies of a
chromosome.
Down syndrome involves three copies of
chromosome _____.
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Chromosomal Disorders
Down Syndrome Karyotype
Down syndrome
produces mild to
severe mental
retardation.
It is characterized by:
increased susceptibility to
many diseases
higher frequency of some
birth defects
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Chromosomal Disorders
Sex Chromosome Disorders
In females, nondisjunction can lead to Turner’s
syndrome.
A female with Turner’s syndrome usually
inherits only one _____ chromosome
(karyotype 45,X).
Women with Turner’s syndrome are sterile.
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Chromosomal Disorders
In males, nondisjunction causes Klinefelter’s
syndrome (karyotype 47,_________).
The extra X chromosome interferes with
meiosis and usually prevents these
individuals from _______________.
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