May 15

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May 15 850 a.m. Make Up Exam For only one
missed midterm Bring scantron and I.D.
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Sex Determination in Humans
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Sex Determination in Humans 5
stages Chromosomal Determination Gonad
Differentiation Anatomical Differentiation Brain
Differentiation Socialization
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EXAM
Chromosomal Sex Determination Humans 23 pairs of
Chromosomes 22 pairs of Autosomes or Somatic
Chromosomes (same in both sexes) 1 pair
of Sex Chromosomes Males 1 Y, 1 X
XY Females 2 X XX
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Human Male Karyotype, XY
Chromosomes 1-22 are autosomes or somatic
chromosomes non-sex chromosomes XY are the sex
chromosomes
http//www.amnh.org/learn/musings/FA01/ia/HW_01.jp
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Normal Human Female Karyotype XX
22 pairs of autosomes 1 pair of sex
chromosomes, XX
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X
Y
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Y chromosome has less than 100 genes .. One
gene is for
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Additional genes found on Y chromosome Inability
to see and hear the obvious gene Inability to
express affection over the phone gene Posturing
in presence of other males gene Refusal to ask
questions when lost gene Channel flipping
gene Male Sports Bonding gene Addiction to death
and destruction movies gene Preadolescent rock
throwing gene Preadolescent attraction to spiders
and insects gene Spitting gene
X
Y
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EXAM
Y chromosome
Male anatomy, physiology, behavior
SRY (HY) gene
SRY (H-Y) protein
X chromosome
Female anatomy, physiology, behavior
w/o SRY (HY) gene
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Primitive gonad or ovotestes unspecialized
H-Y Gene
w/o H-Y Gene
Testes
ovary
Testosterone
Estrogens
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• Gonad Differentiation - Male
• H-Y or SRY Gene (on Y Chromosome)
• H-Y Protein (SRY protein)
• Inner part of ovotestes becomes testes
• Testes makes male hormones
• Male sex organs,
• secondary sex characteristics (muscle,
  skeleton),
• Brain development (for constant
  production of sperm) at 6 weeks

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• Gonad Differentiation Female
• XX
• Absence of Y chromosome (no H-Y gene)
• Outer ovotestes develops into ovary at about
  week 12
• Ovary produces female hormones
• sex organs
• secondary sexual characteristics (muscle,
  skeleton)
• absence of male hormones at week 6 allows
  brain to develop menstrual cycle at puberty.

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Little estrogen
Little testosterone
Mostly testosterone
Mostly Estrogens
Female
Male
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Some abnormalities associated with X and Y
chromosomes
Crossing over of H-Y gene
X Y
X Y
Spermatogenesis
H-Y gene
H-Y gene crosses over to X chromosome
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Sperm with X with H-Y gene
X
X
X
X
Zygote XX (genetic female) Phenotype male,
because of the H-Y gene
Egg with normal X without H-Y gene
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Sperm with Y without H-Y gene
Y
Y
X
X
Zygote XY genetic male Phenotype female
because of absence of H-Y gene
Egg with normal X without H-Y gene
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EXAM
Conclusion Absence of H-Y gene usually
female female is automatic unless H-Y gene is
present
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Another Chromosomal Abnormality Androgen
Insensitivity XY Embryo Faulty Processing of
testosterone Embryo not conditioned as
male Embryo automatically develops into normal
looking female Develops into female with XY
chromosomes Normal breast development no
uterus no oviducts vagina present internal
testes present no sperm
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Primary Oocyte
Non-disjunction
Secondary Oocyte
ovum
zygote
zygote
Extra black chromosome
Missing a black chromosome
sperm
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Klinefelters Syndrome
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Klinefelters Syndrome
XXY 22 pairs of
autosomes
male with some female characteristics
EXAM
XX Egg 22 autosomes

Y Sperm 22 autosomes

1. Normal male until puberty, 2. Testes not
normal, 3. Tall,
4. Female musculature,
5. Some breast development, 6. High
pitched voice, 7. Usually sterile,
8. XXXY more extreme
XXY Zygote 44 autosomes

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Trisomy X Syndrome
XXX 22 pairs of
autosomes
female
EXAM
XX Egg 22 autosomes

X Sperm 22 autosomes

1. Normal Female, 2,
Normal appearance, 3. May be
sterile or fertile,
4. May have mental retardation,
5. 1 in 1200
births, 6. XXXX more
extreme
XXY Zygote 44
autosomes
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Turners Syndrome 22 pairs of autosomes and X0
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Turners Syndrome
X0 22 pairs of
autosomes
female
EXAM
No X Egg 22 autosomes

X Sperm 22 autosomes

• Characteristics
• Normal female until puberty,
• Lack of normal ovary development,
• sterile
• Remain childlike throughout life
• Normal intelligence
• 1 per 2500 births

X0 Zygote 44 autosomes

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XYY Syndrome
XYY 22 pairs of
autosomes
Male
EXAM
X Egg 22 autosomes

YY Sperm 22 autosomes

Male Lower than normal intelligence Tall Aggressiv
e disproven Prison - disproven
XYY Zygote 44
autosomes
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Early Death Syndrome
Y0 22
pairs of autosomes
Male ?
EXAM
No X Egg 22 autosomes

Y Sperm 22 autosomes

Dies as embryo Too many genes missing with X
Y0 Zygote 44 autosomes

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All chromosomes are capable of forming a trisomy
condition. The most common is chromosome 21.
Trisomy 21 is also known as Downs Syndrome
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Trisomy 21 Downs Syndrome 3 chromosome
21 Results in physical defects and mental
retardation Frequency increases with mothers
age Why? Prophase I occurs before birth,
Anaphase I occurs 12-50 years later More
ionizing radiation picked up in older womans
lifetime resulting in nondisjuctions All
chromosomes can have trisomy
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Primary Oocyte
Non-disjunction
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21
Secondary Oocyte
21
21
21
21
21
21
ovum
21
21
21
zygote
21
zygote
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Extra black chromosome
Missing a black chromosome
sperm
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In Trisomy 21, chromosomes 21 do not separate
after crossover
Younger women
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21
Older women
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EXAM
Trisomy 21 increases with Mothers age
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Triploid (3N) male karyotype individual
appeared normal except for slightly smaller lower
jaw.
This person also has Klinefelter, XXY
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Triploid Watermelon - seedless
Triploid carp - sterile
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Barr Body inactivates one of the X chromosomes in
XX cells after embryo is properly developed
sexually
http//www.mun.ca/biology/scarr/Barr_Bodies.jpg
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XGreen
XPink
XX zygote
Mitosis
XP
XG
XG
XP
Mitosis
Mitosis
Active XG cell line
Active XP cell line
Female mosaic
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XGreen
XGreen
XX zygote
Mitosis
XG
XG
XG
XG
Mitosis
Mitosis
Active XG cell line
Active XG cell line
Female all green
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Anhidrotic Ectodermal Dysplasia N dominant,
normal allele on X chromosome n recessive
allele carried on X chromosome resulting in no
teeth and no sweat glands XNXN normal
female XnXn female with few or no teeth and no
sweat glands XNXn female parts of jaw with
teeth and parts without teeth parts of skin
with sweat glands, parts without sweat
glands. XNY normal male XnY male with no teeth
and no sweat glands
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No teeth, no sweat glands
XNXn female
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Calico Cats (normally all females) B allele
for black fur, on X chromosome O allele for
orange fur, on X chromosome XBXB All black fur,
female cat XOXO All orange fur, female cat XBXO
Black and orange, female cat (Calico) XBY Black,
male cat XOY Orange, male cat XBXOY Black and
orange, male (Klinefelter, Calico)
XBXO
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Conclusion always one fewer Barr Body than X
chromosomes
EXAM
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Notice that two of the X chromosomes have Barr
bodies causing them to be inactive