Chromosomal Mutations

1
Chromosomal Mutations

• Changes in Chromosome Number or
  StructureAlterations of Inheritance Patterns by
  Gender

2
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

3
Aneuploidy

• Arises by Non-disjunction
• Non-disjunction failure of homologues or
  chromatids to separate during meiosis

4
Human Chromosomal Aneuploids
Autosomal Aneuploids
Trisomy three copies of one chromosome
5
Human Autosomal Abnormality
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)
6
Karyotype for Down Syndrome
Physical Features
Eye fold
Palm Crease
7
Incidence of Down Syndrome Increases with
Maternal Age
Number per 1000 Births
Age of Mother (years)
8
Applying Your Knowledge

• Polyploidy
• Non-disjunction
• Aneuploidy
• Crossing-over
• Trisomy

• Which one involves the loss of one chromosome
• Which one describes the failure of chromatids to
  separate in Anaphase II
• Which one involves the gain of an extra set of
  chromosomes
• Which is the most specific description for the
  cause of Down Syndrome

9
Human Chromosomal Aneuploids
Sex Chromosome Aneuploids
Sterile female
Fertile female
Sterile male
Fertile male
10
Human Sex Chromosome Abnormality
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)
11
Karyotype for Turners Syndrome
Non-functional Ovaries From Adult Female with
Turners Syndrome
Normal uterus tubes and ovaries
12
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)
13
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
14
Applying Your Knowledge
Determine how many Barr bodies would be found in
each cell of someone with
0
2
1
0
15
Chromosome Structure Changes
16
Chromosome Deletion in Humans

• Cri-du-chat syndrome
• is correlated with
• a deletion at the end
• of chromosome 5.

17
Chromosome Duplication in Humans

• Small duplications in chromosome 15 cause no
  symptoms
• Large duplication (with inversion) causes
  seizures and mental retardation

18
Chromosome Translocation in Humans

• Reciprocal Translocation involves exchange
  between two non-homologous chromosomes
• Reciprocal translocation between chromosomes 2
  and 20 causes Alagille Syndrome

19
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

20
Chromosome Inversions Lead to Unbalanced Meiotic
Products
A paracentric inversion does not include the
centromere
A pericentric inversion includes the centromere
21
Applying Your Knowledge

• Deletion
• Duplication
• Inversion
• Translocation

• Which type of structure change
• represents an exchange between two non-homologous
  chromosomes
• represents a reversal of a chromosome segment
• represents a loss of a chromosomal segment

22
Interaction between Gender and Heredity
Example Pattern BaldnessCaused by a dominant
allele in malesbut a recessive allele in females
23
Interaction between Gender and Heredity
Cock-feathered male
Hen-feathered female
Hen-feathered male
Cock feathering autosomal recessive Expressed
only in males
24
Interaction Between Gender and Heredity
Angelman SyndromeDeletion on chromosome 15
inherited from mother
Prader-Willi SyndromeDeletion on chromosome 15
inherited from father