Maleness in Humans

1
Chapter 5

• Part 2

2
Maleness in Humans

• Been looking for the cause of sex determination
  in humans for 100 years
• von Winiwarter saw 47 chromosomes in
  spermatogonial metaphase preparation, thought
  female had 48 and extra
• Painter observed 45 to 48 in testicular tissue
  saw the small Y-chromosome, favored 46
  chromosomes as 2n number in human but published
  48 chromosomes
• 30 years later, show 46 chromosomes during
  metaphase stages

3
Karyotype

• Female XX

• Male X Y (determines maleness)

4
Aberrant Sexual Development

• Aberrant sexual development is determined by the
  presence of other than normal number of sex
  chromosomes
• list the number of chromosomes present and then
  the deviation from the normal diploid number
• Klinefelter syndrome 47, XXY
• Turner syndrome 45, X

5
Klinefelter Syndrome

• Male genitalia and internal ducts but testes are
  rudimentary and fail to produce sperm
• Tall, long arms and legs, big hands and feet
• Feminine sexual development isnt suppressed
  gynomastica, get breast enlargement, round hips
• Intelligence is below normal range
• 2 in 1000 males

6
Turner Syndrome

• Female genetalia and ducts but ovaries are
  rudimentary
• Short stature, skin flaps on back of neck
• Underdeveloped breasts, broad shield-like chest
• Intelligence is usually normal
• 1 in 2000, many 45,X die in utero and are
  spontaneously aborted

7
Causes of Syndromes

• Both result from non-disjunction and failure of
  chromosomes to segregate properly during meiosis
• Y determines maleness even in the presence of 2
  Xs in Klinefelter syndrome make a male even when
  incompletely expressed
• even only a single X creates a female

8
Additional Information

• Klinefelter syndrome can also have additional Xs
  48, XXXY, 48, XXYY, 49, XXXXY, etc
• the more Xs the more serious the disorder
• Turner syndrome can be other than 45, X
• includes the mosaics somatic cells have 2
  different genetic cell lines , each different
  karyotypes, arise from mitotic error in early
  development
• 45, X/46, XY 45, X/46, XX
• start out normal and then show a mixture of
  karyotypes, exhibits varying aspects of syndromes

9
47, XXX Syndrome

• Female differentiation
• Normal autosomes and 3 Xs 1 in 1200 births
  highly variable in expression
• range from perfectly normal undeveloped
  secondary sexual sex characteristics, sterility
  and mental retardation
• Also see 48, XXXX and 49, XXXXX may be more
  pronounced
• extra X seems to disrupt balance of genetic info
  essential for normal female development

10
47, XYY Condition

• Additional Y in normal male karyotype
• 9 of 315 in Scottish prison were 47, XYY
• above average height, antisocial (non-violent)
  crimes
• 7 were subnormal intelligence, all had
  personailty disorders
• In criminal and normal population see height and
  subnormal intelligence in both, but increased
  karyotype in prisons and mental institutions
• probably no correlation between extra Y and
  behavioral problems

11
Sexual Differentiation in Humans

• Y chromosome is responsible for maleness
• Early development of the embryo has a period that
  it is potentially a hermaphrodite
• gonadal promodia arise as ridges associated with
  embryonic kidney, it has an outer cortex that
  will become the ovary and the inner medulla that
  will become the testes
• each embryo has 2 sets of tubes
  undifferentiated male (Wolffian) and female
  (Mullerian) ducts if XY then medulla begins to
  form testes in week 7, no XY then ovaries from
  with appropriate duct system, unused ducts
  degenerates
• embryonic testicular tissue secretes 2 hormones
• without male development ovary oogonia undergo
  meiosis beginning in the 12th week and completed
  by 25th week, males primary spermatocytes not
  produced until puberty