Transcript Chapter 17- Sex Determination

Chapter 17- Sex Determination
•Aristotle- Women are men with ______________ development
•Pre-1900s- Sex considered to be determined by
environment, age, nutrition
•Early 1900s- Sex chromosome identified
1. Primary sex determination
•Refers to “determination of ____________”
i.e. _______ vs. _________
In Mammals• Strictly determined by the __ chromosome
XY, XXY, XXXY, XXXXY are all ______
•There is no “default state”- gonad development is __________
2. Secondary sex determination
•Refers to “____________________”
i.e. penis and prostate vs vagina and uterus
Also may affect body shape and size, voice….
•Dictated by ____________ produced by ______
If remove ______- female body is the “_________”
Estrogen and testosterone play key roles
•Estrogen instructs Mullerian Duct to become ___________________
•Testosterone instructs Wolfian Duct to become ____________,
vas deferens
•Testes also secrete ____ hormone to _________ Mullerian Duct
Gonad development
Gonads derived from ___________
____________________, next to kidneys
Recall Kidney
development
from Ch. 14
Nephric
Duct
Gonad
Intermediate
Kidney,
gonads
nephros
Migrating nephric
duct cells induce
surrounding
mesenchyme to form
nephros (tubules)
Developing
kidney
The nephric duct is also
called the_______________
Fig. 14.18
Gonad development
Gonads
__________
duct
Kidney
__________duct
(nephric duct)
• Unlike other tissues,
the gonad has two
options- an ______or
a ________
Genital ridge
Bipotential gonad
SF1
WT1
LHX9
Gonad development
• Genital ridge forms
by ________ in human
4 weeks
Genital ridge
• Sex cords formed in
gonad by _________
Sex cords
6 weeks
• Now germ cells migrate
into __________
At this stage, the gonad is still ________________
If male:
Wolffian Duct
•If male, _________ development
continues, become ____________
that link to ___________________
•Mullerian duct __________
Testis cords
8 weeks
•Testis cords remain solid until
__________
• At puberty, testis cords are
_____________ to form
______________ and germ cells
differentiate into _________
16 weeks
The wolffian duct becomes___
_______ to carry sperm to ________
If female:
•If female :
•sex cords _____________
•ovaries to not connect to
_______________
•__________ sex cords are
generated around germ cells
Cortical sex cords
Wolffian Duct
8 weeks
•Cortical sex cords plus
surrounding mesenchyme will
eventually become the __________
that envelop the ___________
•The Mullerian duct becomes _______
uterus, cervix and _______________
Mullerian
Duct
•Wolffian duct _________
16 weeks
Follicles
Another view of sex determination
Bipotential gonads
Both Wolfian and
Mullerian ducts are present
prior to _____________
Kidney
Mullerian
duct
Wolfian
duct
Either Wolfian and
Mullerian duct must be
degraded
But, what dictates
testes vs ovaries??
Male
Female
Fig. 17.4
Mechanisms of Primary sex determination in mammals
SRY is the ______________________ gene.
•SRY expression directs male _____________
•Located on the Y chromosome
• encodes a ____ AA peptide
• is a ___________________
Extra DAX
•contains a HMG domain, common in many transcription factors
•induces bends in DNA
•SRY gene into XX mouse results in a
___________ mouse
•Is ___________ but not ____________ to
dictate testes
•Other genes include _______ and ______
_______ may be the ovary-determining gene
•DAX located on X chromosome
•Two copies of DAX results in ___ female
Two copies of
____ overrides
the _____ gene:
• ______ is also
critical for ovary
formation
If insert second DAX gene on X chromosome
X X
X Y
Testis
Ovary
Gonadal
dysgenesis
Male
Female
Female
X Y
(Poorly
formed
gonad)
Model to explain primary sex determination in mammals
Fig. 17.10
SRY competes with _____ to activate or repress the ____ gene.
• If X + Y : ____ favored, SF1 expressed, _____ produced
•SF1 may also inhibit ____ expression
• If X (w/ 2____) + Y : SF1 repressed, ____ expressed,
and ________ produced
Mechanisms of _________ sex determination in mammals
Testes secrete two _________
1. ______- results in Mullerian duct degeneration
Probably through apoptosis
2. _______________- results in Wolffian duct
differentiation
_____________ insensitivity syndromelack testosterone receptor, thus have testes
but no uterus/oviducts; hence looks female
Ovaries secrete __________
Estrogen is required for development of
both _________ and _____________ ducts
Fig. 17.11
Estrogen also promotes ___________ development
In contrast to humans,
a. Drosophila sex is determined by the number of
___ chromosome ratio (where A is an autosome)
X- male
XX- female
•The Y chromosome is active in _________ development
b. Turtle and crocodile sex is
determined by __________% male
c. The slipper snail sex is
determined by ___________
Individuals are always _____,
then can turn into _________
Temp
Fig. 17.20
Sex determination in
Drosophila
• XX = females
• XY = males
Unlike mammals, the Y chromosome does not determine sex
How is sex determined??
Answer: The X to autosome _____________ determines sex
How is the X:A ratio interpreted??
Answer: Through activation of the _____________ gene
• It is a ____________ between numerator proteins (on
X) and denominator proteins (on A)
__________ (X) proteins
__________Sxl
transcription
___________ (A) proteins
________ Sxl gene transcription
UGA
PL
PE
Sxl gene
2
1
• In males, the _________ proteins win out
• In females, the __________ proteins win out
The Sxl protein acts on:
1 Sxl gene “____” promoter (PL) to maintain
transcription
2 Sxl mRNA to splice out a _____________
3
3
__________gene to splice out __________
1
2
3
4
DNA
RNA
AAAAA
Female mRNA
Pre- mRNA
Male- mRNA
Sex-lethal
Stop codon
Stop codon
transformer
Stop codon
Stop codon
doublesex
Fig. 17.18
Sxl controls splicing of tra switch controls splicing of_________ (dsx)
•Double sex in produced in both sexes, but ____________ protein
is generated due to alternate splicing.
Thus, the _____ protein type dictates _____
• A _____________ similar to dsx has been isolated