chapter 17- sex determination
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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 ____________ ” - PowerPoint PPT PresentationTRANSCRIPT
Chapter 17- Sex Determination
•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 __________
•Aristotle- Women are men with ______________ development
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 developmentGonads derived from ___________ ____________________, next to kidneys
Intermediate
Kidney, gonads
Gonad
nephros
Developing kidney
Nephric Duct
Fig. 14.18
Recall Kidney development from Ch. 14
Migrating nephric duct cells induce surrounding mesenchyme to form nephros (tubules)
The nephric duct is also called the_______________
Gonad development
• Unlike other tissues, the gonad has two options- an ______or a ________
Genital ridge Bipotential gonadSF1WT1LHX9
Kidney
Gonads
__________duct (nephric duct)
__________duct
Genital ridge
Sex cords
4 weeks
6 weeks
Gonad development
• Genital ridge forms by ________ in human
• Sex cords formed in gonad by _________
At this stage, the gonad is still ________________
• Now germ cells migrate into __________
•If male, _________ development continues, become ____________ that link to ___________________
•Testis cords remain solid until __________
• At puberty, testis cords are _____________ to form ______________ and germ cells differentiate into _________
If male:
Testis cords
Wolffian Duct
8 weeks
16 weeks The wolffian duct becomes__________ to carry sperm to ________
•Mullerian duct ___________
•If female :•sex cords _____________•ovaries to not connect to _______________
•The Mullerian duct becomes _______ uterus, cervix and _______________
If female:
Cortical sex cords
Wolffian Duct8 weeks
16 weeks
Mullerian Duct
•__________ sex cords are generated around germ cells
•Cortical sex cords plus surrounding mesenchyme will eventually become the __________ that envelop the ___________
•Wolffian duct _________Follicles
Fig. 17.4
Bipotential gonads
Male Female
Both Wolfian and Mullerian ducts are present
prior to _____________Wolfian
duct
Mullerianduct
Either Wolfian and Mullerian duct must be
degraded
But, what dictates testes vs ovaries??
Kidney
Another view of sex determination
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 ___________________
•contains a HMG domain, common in many transcription factors•induces bends in DNA
_______ may be the ovary-determining gene
•Two copies of DAX results in ___ female
•DAX located on X chromosome
•SRY gene into XX mouse results in a ___________ mouse
•Is ___________ but not ____________ to dictate testes•Other genes include _______ and ______
Extra DAX
X Y X X YX
Testis
Male
Ovary
Female
Gonadaldysgenesis
Female
(Poorly formed gonad)
If insert second DAX gene on X chromosomeTwo copies of ____ overrides the _____ gene:
• ______ is also critical for ovary formation
Model to explain primary sex determination in mammals
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
Fig. 17.10
Mechanisms of _________ sex determination in mammals
Testes secrete two _________
1. ______- results in Mullerian duct degeneration Probably through apoptosis2. _______________- results in Wolffian duct
differentiation
_____________ insensitivity syndrome- lack testosterone receptor, thus have testes but no uterus/oviducts; hence looks female
Fig. 17.11
Ovaries secrete __________
Estrogen is required for development of both _________ and _____________ ducts
Estrogen also promotes ___________ development
a. Drosophila sex is determined by the number of ___ chromosome ratio (where A is an autosome)
X- maleXX- female
•The Y chromosome is active in _________ development
In contrast to humans,
b. Turtle and crocodile sex is determined by __________-
Fig. 17.20
% male
Temp
c. The slipper snail sex is determined by ___________
Individuals are always _____,
then can turn into _________
Sex determination in Drosophila
• XX = females
• XY = malesUnlike mammals, the Y chromosome does not determine sex
Answer: The X to autosome _____________ determines sex
How is the X:A ratio interpreted??
How is sex determined??
Answer: Through activation of the _____________ gene• It is a ____________ between numerator proteins (on X) and denominator proteins (on A)
__________ (X) proteins __________Sxl transcription
Sxl gene
___________ (A) proteins ________ Sxl gene transcription
• In males, the _________ proteins win out• In females, the __________ proteins win out
The Sxl protein acts on: Sxl gene “____” promoter (PL) to maintain
transcription Sxl mRNA to splice out a _____________
PEPL
UGA
1
2
12
__________gene to splice out __________3
1 2 3 4DNARNA AAAAA
3
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
Female mRNA Pre- mRNA Male- mRNA
transformer
doublesex
Stop codon
Stop codon
Sex-lethal
Stop codon
Stop codon