Chromosomal Alterations and Their Impact on Phenotype
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Errors in mitosis or
meiosis can results in
changes in phenotype
Alteration of Chromosome
Structure
Breakage of a chromosome can lead to
four types of changes in chromosome
structure:
◦
Deletion
removes a chromosomal segment
◦
Duplication
repeats a segment
◦
Inversion
reverses a segment within a
chromosome
◦
Translocation
moves a segment from one
chromosome to another
Fig. 15-15
Deletion
A B C D E F G H
A B C E F G H
(a)
(b)
(c)
(d)
Duplication
Inversion
Reciprocal
translocation
A B C D E F G H
A B C D E F G H
A B C D E F G H
A B C B C D E F G H
A D C B E F G H
M N O C D E F G H
M N O P Q R
A B P Q R
Abnormal Chromsome Number
In
nondisjunction
, pairs of homologous
chromosomes do not separate normally
during meiosis
As a result, one gamete receives two of
the same type of chromosome, and
another gamete receives no copy
Human disorders due to
chromosomal alterations…
Alterations of chromosome number and
structure are associated with some
serious disorders
Some types of aneuploidy appear to upset
the genetic balance less than others,
resulting in individuals surviving to birth
and beyond
These surviving individuals have a set of
symptoms, or syndrome, characteristic of
the type of aneuploidy
Fig. 15-13-3
Meiosis
I
Nondisjunction
(a) Nondisjunction of homologous
chromosomes in meiosis
I
(b) Nondisjunction of sister
chromatids in meiosis
II
Meiosis
II
Nondisjunction
Gametes
Number of chromosomes
n
+ 1
n
+ 1
n
+ 1
n
– 1
n
– 1
n
– 1
n
n
Aneuploidy
results from the fertilization of
gametes in which nondisjunction occurred
Offspring with this condition have an
abnormal number of a particular
chromosome
Polyploidy
is a condition in which an
organism has more than two complete
sets of chromosomes
◦
Triploidy (3
n
) is three sets of chromosomes
◦
Tetraploidy (4
n
) is four sets of chromosomes
Polyploidy is common in plants, but not
animals
Polyploids are more normal in appearance
than aneuploids
Chromosome Number/Structure
Disorders…
Down Syndrome
Klinefelter Syndrome
Turner Syndrome
Jacob’s Syndrome (super male)
Edward’s Syndrome
Cri du chat (cry of the cat) Syndrome
Patau’s Syndrome
Wolf-Hirschhorn Syndrome
Assignment…
Form groups
Select a Disorder (1
st
come 1
st
serve)
Research Disorder
◦
Identify Problem
◦
State Symptoms
◦
Life expectancy
◦
Treatments or Cures
Record info on poster paper
Share with class
Errors in mitosis or meiosis can result in changes in phenotype, often due to alterations in chromosome structure such as deletion, duplication, inversion, and translocation. Nondisjunction can lead to abnormal chromosome number, resulting in disorders like aneuploidy. Polyploidy, with extra complete sets of chromosomes, is common in plants. Understanding these chromosomal alterations sheds light on genetic disorders and abnormalities in organisms.
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Presentation Transcript
Errors in mitosis or meiosis can results in changes in phenotype
Breakage of a chromosome can lead to four types of changes in chromosome structure: Deletion removes a chromosomal segment Duplication repeats a segment Inversion reverses a segment within a chromosome Translocation moves a segment from one chromosome to another Alteration of Chromosome Structure
Fig. 15-15 A B C D E F G H A B C E F G H Deletion (a) A B C D E F G H A B C B C D E F G H Duplication (b) A B C D E F G H A D C B E F G H Inversion (c) A B C D E F G H M N O C D E F G H (d) Reciprocal translocation M N O P Q R A B P Q R
In nondisjunction, pairs of homologous chromosomes do not separate normally during meiosis As a result, one gamete receives two of the same type of chromosome, and another gamete receives no copy Abnormal Chromsome Number
Alterations of chromosome number and structure are associated with some serious disorders Some types of aneuploidy appear to upset the genetic balance less than others, resulting in individuals surviving to birth and beyond These surviving individuals have a set of symptoms, or syndrome, characteristic of the type of aneuploidy Human disorders due to chromosomal alterations
Fig. 15-13-3 Meiosis I Nondisjunction Meiosis II Nondisjunction Gametes n 1 n + 1 n 1 n n n + 1 n + 1 n 1 Number of chromosomes (b) Nondisjunction of sister chromatids in meiosis II (a) Nondisjunction of homologous chromosomes in meiosis I
Aneuploidy results from the fertilization of gametes in which nondisjunction occurred Offspring with this condition have an abnormal number of a particular chromosome Polyploidy is a condition in which an organism has more than two complete sets of chromosomes Triploidy (3n) is three sets of chromosomes Tetraploidy (4n) is four sets of chromosomes Polyploidy is common in plants, but not animals Polyploids are more normal in appearance than aneuploids
Down Syndrome Klinefelter Syndrome Turner Syndrome Jacob s Syndrome (super male) Edward s Syndrome Cri du chat (cry of the cat) Syndrome Patau s Syndrome Wolf-Hirschhorn Syndrome Chromosome Number/Structure Disorders
Form groups Select a Disorder (1st come 1st serve) Research Disorder Identify Problem State Symptoms Life expectancy Treatments or Cures Record info on poster paper Share with class Assignment
