Mistakes in Meiosis

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MistakesinMeiosis
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Nondisjunction

• The failure of homologous chromosomes to separate
  properly during meiosis.
• What should happen

Nondisjunction
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The results

• If the abnormal gametes is fertilized the results

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Polyploidy

• the condition where cells have multiple sets of
  chromosomes
• usually 3-4 sets
• Most often found in plants, rare in animals

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Examples of Polyploidy

• Diploid tetraploid
• many plants
• Octoploidy
• strawberries
• Triploid
• seedless watermelon

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Trisomy

• The zygote has an extra chromosome
• Organisms with an extra chromosome sometimes
  survive

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Examples of trisomy in humans

• Trisomy 21 Downs Syndrome
• Trisomy 18 Edwards syndrome
• Trisomy 13 Patau syndrome
• XXY Klinefelter's syndrome

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Trisomy 21 Downs Syndrome

• 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)

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Trisomy 18 Edwards syndrome

• 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

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Trisomy 13 Patau syndrome

• 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

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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

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Monosomy

• The zygote is lacking a chromosome
• Organisms lacking one or more chromosomes rarely
  survive

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Examples of monosomy in humans

• Monosomy X Turners Syndrome

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Monosomy X Turners Syndrome

• 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

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Human Karyotype
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Karyotype Lab

• You will assess a human karyotype and write a
  letter to explain the chromosomal abnormality to
  the patient and patients family.
• You will submit your letter via TurnItIn.com

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