Download Chromosome Number Mutations

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Chromosome Number
Mutations
8.19 to 8.23
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Karyotype

Photographic display of
metaphase chromosomes
arranged by size and
centromere position

Used to identify chromosome
number disorders

Chromosome pairs 1 to 22
 Autosomes

Chromosome pair 23
 Sex Chromosomes

What sex is shown here?
 female
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Down Sydnrome

Trisomy 21
 3 copies of chromosome 21

Symptoms
 Heart and respiratory
defects
 Short in stature
 Flattened nose bridge
 Skin fold in the corner of
eye
 Single skin fold in palm
 Small ears, hands, and feet
 Varying degrees of mental
retardation
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Nondisjunction

Nondisjunction
 Mutation / accident during
cell division
 Homologous chromosomes
fail to separate in meiosis I
 Sister chromatids fail to
separate in meiosis II or
mitosis
 Results in extra or missing
chromosomes

Which has a greater impact
mieotic nondisjuction or mitotic
nondisjuntion? Why?
 Mieiotic – passed to future
generations
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Sex Chromosomes

Why is nondisjunction of sex
chromosomes usually not
fatal?
 Y – contains few genes,
genes that are nonvital,
genes that code for male
characteristics
 X – mammals function with
only one X activated per
cells; if one is missing there
is still one present to code
for vital life functions
 NOTE: one X must be
present, without an X, life
ceases
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Chromosomal Mutations

Deletion -Loss of part of DNA
sequence; eliminate a gene or
alter gene products

Duplication – repetition of part
of a chromosome

Inversion – change in gene
order on chromosome

Translocation – exchange of
genetic material between
nonhomologous chromosomes