Download Chromosomal Mutations

Chromosomal Mutations
Changes in Chromosome
Number or Structure
Alterations of Inheritance
Patterns by Gender
Alterations in Chromosome
Number
• Polyploidy: one or more extra sets of
chromosomes
•Aneuploidy: gain or loss of one
chromosome or a small
number of chromosomes
Aneuploidy
• Arises by Non-disjunction
• Non-disjunction = failure of homologues or
chromatids to separate during meiosis
Normal
Meiosis
Non-disjunction
in Meiosis I
Non-disjunction
in Meiosis II
Human Chromosomal Aneuploids
Autosomal Aneuploids
Down Syndrome
Trisomy 21
Edward Syndrome Trisomy 18
Patau Syndrome
Trisomy 13
Trisomy: three copies of one chromosome
Human Autosomal Abnormality
Down Syndrome
Trisomy 21
Three copies of
chromosome 21
How can Down Syndrome occur?
Eg. Egg with 2 copies of #21 (24 chromosomes)
+ Sperm with 1 copy of #21 (23 chromosomes)
= Embryo with 3 copies of #21 (47 chromosomes)
Karyotype for Down Syndrome
Physical Features
Eye fold
Palm Crease
Incidence of Down Syndrome
Increases with Maternal Age
Number per 1000 Births
400
300
200
100
0
10
20
30
40
Age of Mother (years)
50
Applying Your Knowledge
1.
2.
3.
4.
5.
Polyploidy
Non-disjunction
Aneuploidy
Crossing-over
Trisomy
A. Which one involves the loss of one chromosome?
B. Which one describes the failure of chromatids to
separate in Anaphase II?
C. Which one involves the gain of an extra set of
chromosomes?
D. Which is the most specific description for the
cause of Down Syndrome?
Human Chromosomal Aneuploids
Sex Chromosome Aneuploids
Turner Syndrome
45, XO
Sterile female
Triplo-X
47, XXX
Fertile female
Klinefelter Syndrome 47, XXY
Sterile male
XYY Syndrome
Fertile male
47, XYY
Human Sex Chromosome Abnormality
Turner Syndrome
XO
One copy of X
No second sex
chromosome
How can Turner Syndrome occur?
Eg. Egg with 0 copies of X (22 chromosomes)
+Sperm with 1 copy of X (23 chromosomes)
= Embryo with 1 copy of X (45 chromosomes)
Karyotype for
Turner’s Syndrome
Normal uterus, tubes
and ovaries
Non-functional Ovaries From Adult
Female with Turner’s Syndrome
Human Chromosomal Aneuploids
How can XYY Syndrome occur?
One Copy of the X chromosome
Two Copies of the Y chromosome
Eg. Egg with 1 copy of X (23 chromosomes)
+ Sperm with 2 copies of Y (24 chromosomes)
= Embryo with XYY
(47 chromosomes)
X-Chromosome Inactivation in Females
•Inactivation of one of the X
chromosomes in each cell of an
adult female balances the
sex chromosome/autosome ratio.
• Either the maternal or paternal
chromosome is inactivated.
•The arrow shows a Barr body, or
inactivated X.
•The number of Barr bodies
equals the number of
X chromosomes minus one.
female
male
Applying Your Knowledge
Determine how many Barr bodies would
be found in each cell of someone with:
Turner Syndrome
45, XO
0
Triplo-X
47, XXX
2
Klinefelter Syndrome 47, XXY
1
XYY Syndrome
0
47, XYY
Chromosome Structure Changes
Change
Deletion
Description
Loss of a chromosomal
segment
Duplication Repeat of a chromosomal
segment
Translocation Movement of chromosomal
segment to non-homologous
chromosome
Reversal of a chromosomal
Inversion
segment (rotated 180o)
Chromosome Deletion
in Humans
Cri-du-chat syndrome
is correlated with
a deletion at the end
of chromosome 5.
Chromosome
Duplication
in Humans
 Small duplications
in chromosome 15
cause no symptoms
 Large duplication
(with inversion)
causes seizures
and mental
retardation
Reciprocal
Translocation
involves exchange
between two nonhomologous
chromosomes
Reciprocal
translocation
between
chromosomes
2 and 20 causes
Alagille Syndrome
Chromosome
Translocation
in Humans
Chromosome Translocation in Humans
 Robertsonian Translocation involves a fusion of the long
arms of two different chromosomes
 Translocation Down Syndrome involves a Robertsonian
Translocation between chromosomes 14 and 21
A paracentric
inversion does
not include the
centromere
Chromosome Inversions
Lead to Unbalanced
Meiotic Products
A pericentric
inversion includes
the centromere
Applying Your Knowledge
1.
2.
3.
4.
Deletion
Duplication
Inversion
Translocation
Which type of structure change
a. represents an exchange between two
non-homologous chromosomes?
b. represents a reversal of a chromosome
segment?
c. represents a loss of a chromosomal
segment?
Interaction between Gender and Heredity
Sex-influenced
characteristic
Determined by autosomal genes
Expression differs by gender
Example: Pattern Baldness
Caused by a dominant allele in males,
but a recessive allele in females
John Adams
John Quincy
Adams
bb
BB or Bb
BB or Bb
bb
Interaction between Gender and Heredity
Sex-limited
characteristic
Cock-feathered male
Determined by autosomal genes
Expressed only in one gender
Hen-feathered female
Hen-feathered male
Cock feathering, autosomal recessive
Expressed only in males
Interaction Between Gender and Heredity
Genomic Expression of autosomal genes
Imprinting differs depending on whether they
are inherited from the male or
female parent
Prader-Willi Syndrome
Deletion on chromosome 15
inherited from father
Angelman Syndrome
Deletion on chromosome 15
inherited from mother