Transcript on Y Chromosome

May 15
8:50 a.m.
Make Up Exam
For only one missed midterm
Bring scantron and I.D.
Sex Determination in Humans
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Sex Determination in Humans – 5 stages
Chromosomal Determination
Gonad Differentiation
Anatomical Differentiation
Brain Differentiation
Socialization
Chromosomal Sex Determination
EXAM
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
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.jpg
Normal Human Female Karyotype; XX
22 pairs of
autosomes
1 pair of sex
chromosomes,
XX
X
Y
Y chromosome has less than 100 genes
……………….. One gene is for ……
Additional genes found on
Y chromosome
Inability to see and hear the obvious gene
Inability to express affection over the
phone gene
X
Y
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
EXAM
Y chromosome
Male
anatomy,
physiology,
behavior
SRY (HY) gene
SRY (H-Y) protein
X chromosome
w/o SRY (HY) gene
Female
anatomy,
physiology,
behavior
Primitive gonad or
ovotestes =
unspecialized
H-Y Gene
Testes
Testosterone
w/o H-Y Gene
ovary
Estrogens
2. 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
2.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.
Little
estrogen
Mostly
testosterone
Little
testosterone
Mostly
Estrogens
Male
Female
Some abnormalities associated with X and Y chromosomes
Crossing over of H-Y gene
X
Y
X
Spermatogenesis
H-Y gene
H-Y gene crosses
over to X
chromosome
Y
Sperm with X with H-Y gene
X
X
X
X
Zygote:
XX (genetic female)
Egg with normal X without H-Y gene
Phenotype = male,
because of the H-Y
gene
Sperm with Y without H-Y gene
Y
Y
X
X
Zygote:
XY = genetic male
Egg with normal X without H-Y gene
Phenotype = female
because of absence of
H-Y gene
Conclusion:
EXAM
Absence of H-Y gene usually = female;
female is automatic unless H-Y gene is present
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
Primary Oocyte
Non-disjunction
Secondary Oocyte
ovum
zygote
zygote
Extra black chromosome
sperm
Missing a black chromosome
Klinefelter’s Syndrome
Klinefelter’s Syndrome –
XXY+ 22 pairs of autosomes
male with some female characteristics
XX Egg
+ 22 autosomes
XXY Zygote
+ 44 autosomes
EXAM
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
Trisomy X Syndrome –
XXX+ 22 pairs of autosomes
female
XX Egg
+ 22 autosomes
XXY Zygote
+ 44 autosomes
EXAM
X Sperm
+ 22 autosomes
1.
2,
3.
4.
5.
6.
Normal Female,
Normal appearance,
May be sterile or fertile,
May have mental retardation,
1 in 1200 births,
XXXX more extreme
Turner’s Syndrome = 22 pairs of autosomes and X0
Turner’s Syndrome –
X0 + 22 pairs of autosomes
female
No X Egg
+ 22 autosomes
EXAM
X Sperm
+ 22 autosomes
Characteristics:
1. Normal female until puberty,
2. Lack of normal ovary
development,
X0 Zygote
+ 44 autosomes
3. sterile
4. Remain childlike throughout life
5. Normal intelligence
6. 1 per 2500 births
XYY Syndrome –
XYY + 22 pairs of autosomes
Male
X Egg
+ 22 autosomes
EXAM
YY Sperm
+ 22 autosomes
Male
XYY Zygote
+ 44 autosomes
Lower than normal intelligence
Tall
Aggressive – disproven
Prison - disproven
Early Death Syndrome –
Y0 + 22 pairs of autosomes
Male ?
No X Egg
+ 22 autosomes
Y0 Zygote
+ 44 autosomes
EXAM
Y Sperm
+ 22 autosomes
Dies as embryo
Too many genes missing with X
All chromosomes are capable of
forming a trisomy condition.
The most common is
chromosome 21.
Trisomy 21 is also known as
Down’s Syndrome
Trisomy 21 – Down’s Syndrome
3 chromosome #21
Results in physical defects and mental
retardation
Frequency increases with mother’s age
Why?
Prophase I occurs before birth,
Anaphase I occurs 12-50
years later
in
More ionizing radiation picked up in
older woman’s lifetime resulting
nondisjuctions
Non-disjunction
21
21
21
21
Primary Oocyte
Secondary Oocyte
21
21
21
21
21
ovum
21
21
21
zygote
zygote
Extra black chromosome
21
sperm
Missing a black chromosome
In Trisomy 21, chromosomes 21
do not separate after crossover
Younger women
21
21
Older women
EXAM
Trisomy 21 increases
with Mother’s age
Triploid (3N) male karyotype – individual appeared
normal except for slightly smaller lower jaw.
This
person
also has
Klinefelter,
XXY
Triploid Watermelon seedless
Triploid carp - sterile
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
XGreen
XPink
XX zygote
Mitosis
XG
XG XP
XP
Mitosis
Active
XP
Mitosis
Active XG cell line
cell line
Female mosaic
XGreen
XGreen
XX zygote
Mitosis
XG
XG XG
XG
Mitosis
Active
XG
Mitosis
Active XG cell line
cell line
Female all green
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
No teeth, no sweat glands
XNXn female
http://www.bitein.com/images/reshma02.jpg
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
XBXO
Black and orange, male (Klinefelter, Calico)
EXAM
Conclusion – always
one fewer Barr Body
than X chromosomes
Notice that two of
the X
chromosomes
have Barr bodies
causing them to be
inactive