Tools & Traits
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"Gene mapping" refers to the mapping of
genes to specific locations on chromosomes.
It is a critical step in the understanding of
genetic diseases.
There are two types of gene mapping
 Genetic Mapping - using linkage analysis to
determine the relative position between two
genes on a chromosome.
 Physical Mapping - using all available techniques
or information to determine the absolute position
of a gene on a chromosome.
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If two loci of a single chromosome are usually
inherited together, they are said to be "linked".
genes on the same chromosome are less likely to
be separated by crossing-over the closer they
are to each other on the chromosome..
the more frequent recombination rates of genes
of the same chromosome, or linkage group,
would mean the further apart they existed on
that chromosome
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This uses laboratory cultured cells and
chromosomes isolated by mechanical means
to study nucleotide sequences through a
variety of techniques.
 Restrictive enzyme analysis
 Fluorescence techniques FISH
 contigs
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Recombinant DNA
Cloning
Stem cells
These techniques and tools have to date
involved the use of bacteriophages and
viruses to carry DNA/RNA segments to cells
in culture.
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Karyotyping
 A method of organizing the chromosomes of a
cell in relation to number, size, and type.
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Useful to see obvious abnormalities of
chromosome structure and numbers.
Chromosomes are categorized and sorted by
 Size of the chromosome
 placement of the centromere
 Relative lengths of arms
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A diagram shows inheritance patterns over
several generations and can give many key
clues as to the kind of inheritance a particular
trait exhibits.
Based on physical expression or phenotypes
Ex: whether a trait is
dominant / recessive or sex-linked
Pedigrees are an important tool for
understanding the pattern of inheritance of
human genetic traits and disorders
Generations are numbered from
the top of the pedigree in
uppercase Roman numerals, I, II, III
Individuals in each generation are
numbered from the left in arab
numerals 1, 2, 3
Draw the information one step at a time in a logical manner.
Step 1
Begin with Alice, Bob and Charles.
Step 2
Now add Alice's siblings and parents to the pedigree.
Step 3
Now add Gertrude's siblings to the pedigree.
And David's siblings and his nephews and nieces
Finally add Bob's side of the family
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Traits controlled by a single allele:
 These traits are controlled by a single gene , or pair of
alleles,
 They may be dominant or recessive
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Some traits may be controlled by more than a
single pair of alleles.
 3 or more alleles of the same gene may exhibit
codominance
 More than one gene may control expression as in
polygenic trait
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Some traits are said to be sex-linked.
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most often single allele recessive traits
carried on a sex chromosome
more rarely expressed.
Ex. Colorblindness and hemophilia.
Some traits are sex influenced.
 The traits in this category are expressed differently in
males and females
 Influenced by sex hormones.
 Ex. Pattern baldness.
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These genetic diseases are diseases caused
by an error in a single gene.
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Some examples of autosomal dominant
diseases are Huntington's disease and
achondroplasia (dwarfism).
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No carriers: Everyone who has the genetic error
gets the disease,
Usually inherited: For a person to have the
disease, one of the parents must have had the
disease.
Parent-to-child transmission: The same
probabilities apply as in the inheritance of any
simple dominant gene
Vertical inheritance: Every generation is
affected, called a "vertical" pattern, as seen on a
family tree..
Gender bias: Male or females get the disease
equally, because an autosomal error is unrelated
to the sex chromosomes.
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These genetic diseases are diseases caused
by an error in a single DNA gene.
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Some examples are diseases are Cystic
Fibrosis, Phenylketonuria, Sickle Cell Anemia,
Tay Sachs, and Albinism.
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Parent – child transmission: Typical
probabilities of recessive gene alleles apply.
Carrier: Any heterozygous state for a recessive
allele constitutes a carrier state.
Gender bias: Male or females get the disease
equally, because an autosomal error is unrelated
to the sex chromosomes.
Horizontal Inheritance: patterns tend to be
"horizontal", which a generation being affected
(i.e. many siblings of the same parents), but not
their parents nor their own children. Parents and
next-generation children will usually be carriers.
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These genetic diseases are diseases caused
by an error in a single gene located on a sex
chromosome of pair #23.
Examples: red-green color blindness and
hemophillia
May exhibit dominance or recessiveness
although donimant sex-linked is very rare and
usually lethal
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Sex-influenced inheritance is a pattern of
inheritance in which the sex hormones of the
animal affect the expression of a trait by the
heterozygotes.
May be male dominant or female dominant
Example “pattern baldness” and the gene
that controls the length of the index finger to
be longer than the 3rd finger
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A Mutation occurs when the DNA of a gene is
damaged or changed in such a way as to alter
the genetic message carried by that gene.
It may be inherited or acquired
A Mutagen is an agent of substance that can
bring about a permanent alteration to the
physical composition of a DNA gene such
that the genetic message is changed.
Mutation
In subtle or very obvious ways,
the phenotype of the organism
carrying the mutation will be
changed
the enzyme that is
catalyzing the production of
flower color pigment has
been altered in such a way
it no longer catalyzes the
production of the red
pigment.
No product (red pigment) is
produced by the altered protein.
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Chemical Mutagens
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Radiation
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Sunlight
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Spontaneous
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Point mutations
 small (but significant) changes. often in a single nucleotide
base.
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Deletions
 remove information from the gene. A deletion could be as
small as a single base or as large as the gene itself.
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Insertions
 occur when extra DNA is added into an existing gene
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Frame shift mutations
 either addition or deletion of one or two nucleotide bases.
When this occurs the "reading frame" is changed so that
all the codons read after the mutation are incorrect, even
though the bases themselves may be still present
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Deletions
 Due to chromosome breakage a piece may be lost
thus losing information forever
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Inversion
 This is when a chromosome segment breaks off and
the reattaches in an inverted orientation
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Translocation
 A chromosome segment breaks off and reattaches to
a non-homologous chromosome.
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Non-dysjunction
 occurs during meiosis when homologous pairs fail to
separate causing one gamete to have an extra
chromosome and the other to have one less.
Non-dysjunction