Download Chromosomal Mutations

BIOLOGY 12
CHROMOSOMAL MUTATIONS
referenced Horton High E-Biology
Chromosomal Mutations
 changes in chromosomal number
 changes in chromosomal structure
Chromosomal Number
 monosomy occurs when and individual has only one
of a particular type of chromosome
 trisomy occurs when and individual has three of a
particular type of chromosome
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monosomy and trisomy occur in plants and animals
 generally lethal in the body cells of animals
nonlethal human monosomies and trisomies include
the following:
 Turner syndrome: monosomy where the individual has
single X chromosome
 Down syndrome is most common trisomy among
humans; it involves chromosome 21
Chromosomal Number cont.
 nondisjunction is the failure of chromosomes to
separate
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it is more common during meiosis I than meiosis II
it can occur in mitosis
 polyploidy: offspring end up with more than two
complete sets of chromosomes
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polyploidy does not increase variation in animals,
would likely be lethal
polyploidy is a major evolutionary mechanism in plants
successful polyploidy results in a new species
Chromosomal Structure
Disorders
 Down syndrome
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most common autosomal trisomy, involves chromosome 21
Down syndrome child has tendency for leukemia, cataracts, faster
aging, and mental retardation
 Turner (XO) syndrome
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females have only one sex chromosome, an X
Turner females are short, have broad chest and webbed neck
ovaries of Turner females never become functional; therefore, do not
undergo puberty
 Klinefelter syndrome
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males have one Y chromosome and two or more X chromosomes
affected individuals are sterile males; testes and prostate are
underdeveloped
individuals have large hands and feet and long arms and legs
Disorders cont.
 Triplo-X females
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have three or more X chromosomes
there is no increased femininity; most lack any physical
abnormalities
there is an increased risk of having triplo-X daughters of
XXY sons
may experience menstrual irregularities, including early
onset of menopause
 XYY males with Jacob syndrome
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have two Y chromosomes instead of one
results from nondisjunction during meiosis II
usually taller than average; suffer from persistent acne; tend
to have lower intelligence
earlier claims that XYY individuals were likely to be
aggressive are not correct
Disorders cont.
 Fragile X Syndrome
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X chromosome is nearly broken; most often
found in males
as children: hyperactive or autistic; delayed
speech; account for part of higher proportion
of males in institutions for mentally retardation
as adults: large testes, unusually protruding
ears
occurs in females, but symptoms are less
severe