Prayer Next Prayer Attendance

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PrayerNext PrayerAttendance
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Chapters 6.14-6.18
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Meiosis I Review
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Meiosis II Review
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Worksheet 3
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Formation of Sex Cells in Humans

• The formation of gametes in animals is called
  gametogenesis
• In humans, gametes are produced in the testes
  (males) and in the ovaries (female)

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Spermatogenesis (Males)

• A primary spermatocyte (diploid sex cell)
  undergoes meiosis I and II and forms 4 spermatids
  (haploid), which will develop into sperm
• Males can produce one billion sperm cells every
  day!

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Oogenesis (Females)

• A primary oocyte (diploid sex cell) undergoes
  meiosis I, but the division of the cytoplasm is
  unequal, resulting in the formation of a polar
  body
• The larger cell (ootid) and the polar body both
  go through meiosis II
• However, the polar bodies die and the nutrients
  are absorbed by the body
• Only one egg (ovum) is produced by meiosis
• Women have about 300 000 oocytes, of which only
  400 500 will be released during the
  reproductive years

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Worksheet 4
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Sex Chromosomes

• sex chromosomes the pair of chromosomes that
  have a role in the sex of an individual
• autosomes the chromosomes not involved in sex
  determination
• Although they are physically different, the X and
  the Y chromosomes are able to synapse for part of
  their length and function as homologous
  chromosomes during meiosis.

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Sex Determination in Humans

• In humans, xx is female, xy is male.
• Sex determination depends on the sex chromosome
  inherited from the father, who is xy.

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Sex Determination in Non-Humans

• In birds, the mother determines the sex of the
  child.
• WZ is female, ZZ is male
• In ants, bees, and wasps, sex is determined by
  the number of chromosome sets an individual has.
• males are haploid and females are diploid
• In turtles, sex is determined by the environment,
  particularly the temperature at which the eggs
  are incubated.
• HOTfemale, COLDmale

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Amniocentesis

• In Amniocentesis, fetal cells are obtained from 2
  tablespoons of amniotic fluid
• A 3 to 4 inch needle is pushed through the
  abdomen and into the amniotic fluid.
• Do 3 to 4 months after pregnancy.
• This procedure is done without an anaesthetic.
• The cells are then cultured and a karyotype or
  other testing can be done.
• This test can be used to detect genetic disorders
  such as downs syndrome (trisomy 21).

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Chorionic Villus Sampling (CVS)

• CVS- cells are obtained from the chorion of the
  placenta (tissue from the placenta) using a
  syringe.
• A needle is inserted through the abdomen or
  through the vagina and cervix, using the
  ultrasound for guidance.
• Do after 10 or 12 weeks after pregnancy.
• The cells are then cultured and a karyotype or
  other testing can be done.
• This test can be used to detect genetic disorders
  such as downs syndrome (trisomy 21).

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Karyotype Chart

• karyotype chart a picture of chromosomes
  arranged in homologous pairs
• monosomy the condition where there is a single
  chromosome in place of a homologous pair 
• trisomy the condition where there are three
  homologous chromosomes in place of a homologous
  pair

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Abnormal Meiosis Nondisjunction

• Nondisjunction occurs when two homologous
  chromosomes move to the same pole during meiosis.
  The result is that one of the daughter cells will
  be missing one chromosome while the other will
  retain an extra chromosome.
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• -can occur in any cell during mitosis BUT effects
  are most devastating during the formation of sex
  cells in meiosis.
• Can cause Down Syndrome.
• Nondisjunction means doesnt break apart.

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Down Syndrome

• Down syndrome a trisomic disorder in which a
  zygote receives three homologous chromosomes for
  chromosome pair number 21
• -regardless of race a round, full face enlarged
  and creased tongue short height and a large
  forehead.
• -1 in 1000 babies is born with Down syndrome

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Down Syndrome

• increased risk as mother gets older

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Turner Syndrome (X)

• Turner syndrome a monosomic disorder in which a
  female has a single X chromosome
• -the individual has 45 chromosomes
• -The only condition where humans can survive
• without one of a pair of chromosomes.
• -1 in every 5000 female babies
• -In 98 of fertilized eggs, the egg is
• spontaneously aborted.

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Turner Syndrome

• short (average is 4 feet and 8 inches)
• web of skin between neck and shoulders
• sterile
• breasts and other secondary sex characteristics
  develop incompletely
• normal intelligence but individuals do have
  learning difficulties

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Klinefelter Syndrome (XXY)

• Klinefelter syndrome a trisomic disorder in
  which a male carries an XXY condition
• -child appears to be a male at birth
• -however, as he enters sexual maturity, he begins
  producing high levels of female sex hormones.
• Males with Klinefelter syndrome are sterile.
• -1 in 1000 males have genotype XXY

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Klinefelter Syndrome (XXY)

• Small testes
• Female features including breast development
• Long limbs. Slightly taller than average. (about
  6 feet)
• Language impairments, speak later.
• Might have more X chromosomes XXXY or XXXXXY.
  These individuals have mental retardation.

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Super Males (XYY)

• occurs in 1 in 1000 males
• very tall (about 6 feet 2 inches)
• moderate to severe acne
• average to slightly lower than average
  intelligence
• most men who are XYY dont even know it!

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Metafemales (XXX)

• occurs in 1 in 1000 females
• sterile
• no other physical or mental problems

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Review
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Worksheet 5
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Lab Part 2

• Tuesday
• http//www.biology.arizona.edu/human_bio/activitie
  s/karyotyping/karyotyping2.html
• Hand in your lab at the end of class.
• Wednesday
• Internet Search Worksheet
• Hand in at the end of class