Transcript Chromosomal Disorders

Chromosomal
Disorders
What happens when meiosis
goes wrong?
Karyotype
Human Chromosomes
• Humans have 46 chromosomes
arranged in 23 pairs
• Two sex chromosomesdetermine an individual’s sex
• Females have two copies of the
large X chromosome
• Males have one X and a smaller Y
chromosome
Human
Chromosomes
• The remaining 44 chromosomes are known as
autosomal chromosomes or autosomes
• Males and females are born in a roughly 50:50
ratio
• All human egg cells carry a single X
• Half of all sperm carry an X and the other half
carry a Y
Male or Female???
Types of Mutations
• Mutations effects vary. One factor is the
type of cell if affects…
• GERM CELLS– Cells that undergo meiosis to produce egg and
sperm cells (in ovaries and testes)
• SOMATIC CELLS– All the “other” body cells that only do mitosis
How would this affect the person
differently?
Types of Mutations
• Chromosomal
mutations involve
changes in the number
or structure of
chromosomes
• Can lead to diseases or
disorders… or (more
rarely) can be
beneficial
Chromosomal Mutations
• Examples:
– Entire chromosome
mutation =
nondisjunction
– “chunk” of a
chromosome mutation=
listed to the right in
diagram (insertion,
deletion…)
Gene/DNA Mutations
• Gene/DNA mutations involve changes in
ONE nucleotide
• Ex’s- Point and Frameshift Mutations
Chromosomal Mutations
• Entire chromosomes encounter mutations as
well
• There are four types:
1.
2.
3.
4.
Deletion
Inversion
Insertion
Translocation
A
B
Gene
C
D
E
Chromosome
Deletion
Before mutation
A
B
C
D
After mutation
E
A
C
D
Occurs when a single break causes a
chromosome to lose an end piece or when
two simultaneous breaks lead to loss of
internal segment
E
Inversion
Before mutation
A
B
C
D
After mutation
E
A
B
C
Occurs when a part of the chromosome
breaks off and is reinserted backwards
E
D
Insertion
Before mutation
A
B
D
C
E
B
A
After mutation
C
B
C
B
C
D
Occurs when a part of the chromosome breaks
off & re-attaches to the same chromosome
resulting in a duplication of genes
E
Translocation
Before mutation
A
B
F
C
G
D
E
H
After mutation
F
A
B
C
G
D
E
H
Occurs when a part of one chromosome breaks
off & attaches to a non-homologous chromosome
Can you spot what is wrong with this karyotype?
Nondisjunction
• Homologous
chromosomes fail to
separate during
meiosis I
OR
• Sister chromatids fail to
separate during
meiosis II
Creates gametes with the wrong number of chromosomes!
Changes in chromosome structure
• Deletion
– Part of a chromosome is
lost during cell division
– Chromosome is missing
genes
• Duplication
– Region of chromosome is
repeated
• Translocation
– Piece of a chromosome
moves to another
chromosome
Figure 1 Left, photograph of
5th Chromosome with a p arm
deletion. Right, Diagram of the
deletion. (Genetic,2003)