Download Errors in Meiosis

 Humans have 22 pairs of non-sex
chromosomes known as autosomes
and one pair of sex chromosomes
 XX – female
 XY - male
 When a chromosome pair doesn’t
separate during meiosis
 One of the gametes might have an
extra chromosome number and
others might have few
error in Meiosis 1
error in Meiosis 2
all with incorrect number
1/2 with incorrect number
 Having an abnormal chromosome
number
 In human cell, instead of 46
chromosomes in each cell, it might
have 45 or 47.
 Almost 6% of all babies are born with
some form of genetic disorder.
 Worldwide, that’s about 8 million
babies every year
There’s an extra chromosome
 Trisomy 13
 Trisomy 18
 Trisomy 21
 Patau Syndrome
 A serious rare genetic disorder caused by
having an additional copy of chromosome
13 in some or all of the body cells.
 This severely disrupts normal development
and, in many cases, results in miscarriage,
stillbirth or the baby dying shortly after birth.
 More than 9 out of 10 children born with
Patau's syndrome die during the first
year.
 About 1 in 10 babies with less severe
forms of the syndrome, such as partial
or mosaic trisomy 13, live for more than
a year.
SYMPTOMS/FACIAL FEATURES
 Anophthalmia
 Hypotelorism
 Problems with the
development of the
nasal passages
 Severe heart
defects
 Holoprosencephaly
 Cleft lip and palate
 Microphthalmia
SYMPTOMS/FACIAL FEATURES
 Microcephaly
 Cutis aplasia
 Ear malformations and deafness
 Raised, red birthmarks
Cause
 Most cases of the syndrome do not run
in families.
 They occur randomly during conception,
when the sperm and egg combine and
the fetus starts to develop.
 Edward Syndrome
 Result from having three copies of
chromosome 18 in each cell in the
body instead of the usual two copies
 Edwards' syndrome affects how long a baby
may survive.
 Most babies with Edwards' syndrome will die
before or shortly after being born.
 A small number, about 13 in 100, babies
born alive with Edwards' syndrome will live
past their 1st birthday.
Symptoms/Facial Features
 Intrauterine growth retardation
 Craniofacial features such as
abnormalities of the jaw, skull, ears, and
neck
 Clenched fists with overriding fingers
 Small fingernails
Symptoms/Facial Features
 Short sternum
 Club feet
 Heart defects
 Kidney defects
 Neurodevelopmental delays
Cause
 Most cases of trisomy 18 are not
inherited, but occur as random
events during the formation of eggs
and sperm
 Down Syndrome
 Occurs because of the extra copy of
chromosome 21, which can cause the
body and brain to develop differently
than a child without the syndrome
 Adults with Down syndrome may live
about 60 years, but this can vary.
SYMPTOMS/FACIAL FEATURES
 Distinctive facial features
 Mild to moderate intellectual disabilities
 Heart, kidney and thyroid issues
 Numerous respiratory infections
 Skeletal abnormalities
 Flexible joints and weak, floppy muscles
SYMPTOMS/FACIAL FEATURES
 Overly quiet baby
 Less responsive to stimuli
 Vision and hearing impairment
 Inwardly curved little finger
Down syndrome & age of mother
Mother’s age
Incidence of
Down Syndrome
Under 30
<1 in 1000
30
1 in 900
35
1 in 400
36
1 in 300
37
1 in 230
38
1 in 180
39
1 in 135
40
1 in 105
42
1 in 60
44
1 in 35
46
1 in 20
48
1 in 16
49
1 in 12
Rate of miscarriage due to
amniocentesis:
1970s data
0.5%, or 1 in 200 pregnancies
2006 data
<0.1%, or 1 in 1600 pregnancies
 A genetic disorder wherein there’s a missing
chromosome
 Example: Turner Syndrome or Monosomy X
 The affected individual has only one X
chromosome.
 In other cases of Turner syndrome, there may
be only part of the second X chromosome
missing, or it may have a structural abnormality.
 Turner Syndrome
 A rare genetic disorder that occurs in girls
 The seriousness of these problems varies
from girl to girl.
 Many of the health problems affecting girls
with Turner syndrome can be managed or
fixed with treatment.
SYMPTOMS/FACIAL FEATURES
 Puffy hands and feet at birth
 Wide neck with folds of skin down the sides of
neck
 Short height
 A low hairline at the back of the neck
 Feeding problems as a baby
 Small differences in the shape and position of the
ears
SYMPTOMS/FACIAL FEATURES
 Broad chest with widely spaced nipples
 More small brown moles on the skin than normal
 Deep-set nails
 Small jaw
 Narrow top of the inside of the mouth
 Skeletal problems
 Eye problems requiring glasses
Klinefelter’s syndrome
XXY male
one in every 2000 live births
have male sex organs, but
are sterile
feminine characteristics
some breast development
lack of facial hair
tall
normal intelligence
Klinefelter’s syndrome
Jacob’s syndrome male
XYY Males
1 in 1000 live male
births
extra Y chromosome
slightly taller than
average
more active
normal intelligence, slight learning disabilities
delayed emotional maturity
normal sexual development
Trisomy X
XXX
1 in every 2000 live births
produces healthy females
Why?
Barr bodies
all but one X chromosome is inactivated