Nondisjunction
Homework for 11/13/14
Fill out notes on the back of page 34, which is the Cell Division Venn Diagram
Nondisjunction
• Although the events of meiosis usually proceed
accurately, sometimes an accident occurs and the
chromosomes fail to separate correctly. This is
known as nondisjunction.
Nondisjunction
• The zygote that has been created will have an extra or missing
chromosome. This would result in an inherited genetic disorder.
oIn most cases, the presence of an additional chromosome or missing
chromosome results in the death of the zygote.
Nondisjunction
Monosomy - the presence of only one chromosome from a pair in a cell's
nucleus.
Trisomy – the presence of three chromosomes instead of 2 in a cell’s nucleus.
Karyotypes
• When you are born, doctors take a sample of your blood and create a
karyotype. This will enable the doctor to see if you have any
additional or missing chromosomes.
• A karyotype is a standardized arrangement of all the chromosomes of
a cell.
Karyotypes
Homologous
chromosomes
are paired up,
then they are
put in order
from the
LARGEST
chromosome
pair to the
smallest.
Karyotypes
Karyotypes
2 different sized sex chromosomes = male
Down’s syndrome
•decreased muscle tone at birth
•asymmetrical or odd-shaped skull
•round head with flat area at the back of the head
•slanting eyes
•small mouth with protruding tongue
•single crease on the palm
•slowed growth and development
•delayed mental and social skills
Turner’s syndrome
• short stature (affects almost all girls with Turner, to different degrees)
• failure of ovaries to develop (90-95% of girls)
• webbed neck (25%) or short neck (40%)
• abnormal fingernails and toenails (70%)
• hearing disorders (50-90%)
• frequent ear infections in childhood (75%)
Turner’s syndrome
Kleinfelter’s syndrome
Kleinfelter’s syndrome
• No symptoms - some men are unaware they have an extra
chromosome
• Enlarged male breasts - only severe in about 10% of cases
• Sparse facial hair
• Sparse body hair
• Inability to produce sperm
• Tallness - more likely to be taller than non-XXY males.
• Thinness
• Normal intelligence
• Language impairment
• Delayed language
Kleinfelter’s syndrome
Patau’s syndrome
Patau’s Syndrome
• Mental retardation, severe
• Seizures
• Small head
• Scalp defects (absent skin)
• Small eyes (microphthalmia)
• Cleft lip and/or palate