Transcript Chromosomal Mutation

Karyotype and Chromosomal
Mutation Notes
What is a karyotype?
• A karyotype is a picture
of chromosomes found in
a typical human body
cell.
• The karyotype is the
result of a haploid sperm
cell, carrying 23
chromosomes fertilizing a
haploid egg cell, carrying
23 chromosomes.
A Normal Human Karyotype
• The chromosomes in a
human karyotype are
arranged in homologous
pairs.
• The first 22 pairs of
chromosomes are called
autosomes.
• The 23rd pair of
chromosomes are known
as the sex chromosomes.
Chromosomal Mutation
B. Chromosomal mutations involve changes in
the number or structure of chromosomes.
Such mutations may change the locations of
genes on chromosomes, and may even change
the number of copies of some genes.
• Chromosomal mutations occur
during crossing over.
• The exchange of genetic material
between homologous pairs of
chromosomes
IV. Chromosomal Mutation
C. Four types of chromosomal mutations:
1) Deletion
2) Duplication
3) Inversion
4) Translocation
1) Deletion
2) Duplication
3) Inversion
4) Translocation
IV. Chromosomal Mutation
D. Deletions involve the loss of all or part of a
chromosome
E. Duplications produce extra copies of all or
part of a chromosome
F. Inversions reverse the direction of parts of
chromosomes
G. Translocations occur when part of a
chromosome break off and attach to another
chromosome.
IV. Chromosomal Mutation
H. Most mutations are neutral – they do not
change the expression of genes or proteins.
I. Some are harmful, some are beneficial.
Nondisjunction
J. Nondisjunction occurs during meiosis when
homologous chromosomes fail to separate.
• Nondisjunction means “not coming apart”.
• When it occurs, abnormal numbers of
chromosomes may find their way into
gametes (sperm or egg), and a disorder of
chomosome numbers may result.
Nondisjunction
Chromosomal Disorders
Down’s Syndrome
Defect – autosomal
disorder (extra copy of
chromosome 21)
Symptoms:
• Have delayed mental
and social development.
Common problems may
include:
• Impulsive behavior
• Poor judgment
• Short attention span
• Slow learning
Down’s Syndrome
• Disorder is also called
trisomy 21. Have an
extra 21st chromosome.
Dominant or Recessive?
– Neither! Due to
nondisjunction.
Down’s Syndrome
Interesting Facts:
- It is usually the egg that provides the extra copies of
chromosome 21
- The older the mother, the chances of having a baby
with Down’s Syndrome increases
- Age 20, 1 in 1500
- Age 40, 1 in 60
Patau Syndrome- Trisomy 13
Symptoms
•
•
•
•
•
•
•
•
•
•
Cleft lip or palate
Clenched hands (with outer fingers
on top of the inner fingers)
Close-set eyes -- eyes may actually
fuse together into one
Decreased muscle tone
Extra fingers or toes (polydactyly)
Low-set ears
Scalp defects (missing skin)
Seizures
Skeletal (limb) abnormalities
Intellectually Disabled
Turner’s Syndrome- XO
Symptoms:
• May be intellectually disabled, some have normal
IQ
• Short stature
• Sterile (cannot have kids)
• Webbed neck
• Underdeveloped breasts
and ovaries
Defect:
• XO (missing a sex
chromosome)
Turner’s Syndrome- XO
Frequency:
1 in 2,500
Interesting Fact:
Caused by non-disjunction.
(Occurs in meiosis when the
sister chromatids aren’t
pulled apart.
Klinefelter’s Syndrome- XXY
Symptoms:
• Underdeveloped testes
• Inability to produce
sperm
• Muscle structure, fat and
hair distribution similar to
that of a female
• Breasts develop
Defect: XXY-Male with an
extra X chromosome in
some cells
Klinefelter’s syndrome
• Dominant or recessive
– chromosomal
mutation XXY
• Frequency – 1 in 400
males
• Interesting fact – often
goes undiagnosed.
Caused by
nondisjunction. Can be
treated with male
hormones.
Eggs
Sperm
Double Y syndrome- XYY
Signs and symptoms:
 Often less than average
IQ
 Tall
 High levels of male
hormones
 Large ears
 Sunken chest
 Delayed speech and
language skills
Defect: Chromosomal
mutation - XYY
Frequency: 1 in 250 males
Interesting fact: Questionable
connection to violent
tendencies