Download File - Mr. Shanks` Class

Mistakes
in
Meiosis
Nondisjunction
• The failure of homologous chromosomes to
separate properly during meiosis.
What should happen
Nondisjunction
The results
• If the abnormal gametes is fertilized the
results
Polyploidy
• the condition where cells have multiple sets of
chromosomes
• usually 3-4 sets
• Most often found in plants, rare in animals
Examples of Polyploidy
Diploid & tetraploid
many plants
Octoploidy
strawberries
Triploid
seedless watermelon
Trisomy
• The zygote has an extra chromosome
• Organisms with an extra chromosome
sometimes survive
Examples of trisomy in humans
• Trisomy 21: Downs Syndrome
• Trisomy 18: Edwards syndrome
• Trisomy 13: Patau syndrome
• XXY: Klinefelter's syndrome
Trisomy 21: Downs Syndrome
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Decreased muscle tone at birth
Separated sutures (joints between the bones of the skull)
Asymmetrical or odd-shaped skull
Round head with flat area at the back of the head (occiput)
Small skull (microcephaly)
Upward slanting eyes, unusual for ethnic group
Small mouth with protruding tongue (see tongue problems)
Broad short hands
Single crease on the palm
Retarded growth and development
Delayed mental and social skills (mental retardation)
Iris lesion (an abnormality of the colored part of the eye called
Brushfield spots)
Trisomy 18: Edwards syndrome
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Most children die in the first year of life, some have lived 10 years
Growth deficiency
Feeding difficulties
Breathing difficulties
Developmental delays
Mental Retardation
Undescended testicles in males
Prominent back portion of the head
Small head (microcephaly)
Low-set, malformed ears
Abnormally small jaw (micrognathia)
Small mouth
Cleft lip/palate
Upturned nose
Narrow eyelid folds (palpebral fissures)
Widely-spaced eyes (ocular hypertelorism)
Dropping of the upper eyelids (ptosis)
Overlapped, flexed fingers
Underdeveloped or absent thumbs
Underdeveloped nails
Webbing of the second and third toes
Clubfeet
Small pelvis with limited movements of the hips
Short breastbone
Kidney malformations
Structural heart defects at birth (i.e., ventricular septal defect, atrial septal defect, patent ductus
arteriosus)
Trisomy 13: Patau syndrome
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Mental retardation, severe
Seizures
Small head (microcephaly)
Scalp defects (absent skin)
Small eyes (microphthalmia)
Cleft lip and/or palate
Eyes close set (hypotelorism) -- eyes may actually fuse together into one
Iris defects (coloboma)
Pinna abnormalities and low set ears
Simian crease
Extra digits (polydactyly)
Hernias: umbilical hernia, inguinal hernia
Undescended testicle (cryptorchidism)
Hypotonia
Micrognathia
Skeletal (limb) abnormalities
XXY: Klinefelter's syndrome
• Klinefelter Syndrome is probably the most
common chromosomal variation found in
humans. In random surveys, it is found to
appear about once in every 500 to one in
every 1,000 live born males.
• sterility, breast development, incomplete
masculine body build, and social and/or
school learning problems
Monosomy
• The zygote is lacking a chromosome
• Organisms lacking one or more
chromosomes rarely survive
Examples of monosomy in humans
Monosomy X: Turners Syndrome
Monosomy X: Turners Syndrome
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Short height
Webbed neck
Drooping eyelids
A "shield-shaped", broad, flat chest
Absent or incomplete development at puberty, including
sparse pubic hair and small breasts
Infertility
Dry eyes
Absent menstruation
Absent normal moisture in vagina; painful intercourse
Karyotyping
• a picture showing the number and type
chromosomes in a cell
• Chromosomes are arranged in order from
largest to smallest
• Shows major chromosomal abnormalities
• i.e. pieces of chromosomes are missing of
extra copies (will not show defective gene)
Human Karyotype