Sex Determination and Differentiation
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19 Terms
Homogametic- female
Heterogametic- male
In humans, who is the homogametic sex? The heterogametic sex?
Heterogametic
Which parents (heterogametic or homogametic) determines the sex of the baby?
Predicted sex ratio- 50M:50F
Primary sex ratio (at fertilization)- 120M: 100F
Secondary sex ratio (at birth)- 105M:100F
In humans, what is the predicted sex ratio? The primary sex ratio? The secondary sex ratio?
Y sperm have less genetic material and can travel faster. XY fetuses are less resilient than XX fetuses
What do the sex ratios suggest?
Klinefelter’s syndrome- extra X chromosome, results in testis (XXY)
Turner’s syndrome- missing Y chromosome, results in ovaries (XO)
The SRY gene is located on the Y chromosome. If the SRY gene is present, testes will develop
What are Klinefelter’s and Turner’s syndrome and how do the resultant gonads make sense given the sex chromosomes present?
Yes
Does the Y chromosome have all the genes needed to make a testis?
Involved in differentiation of the gonadal ridge from the intermediate mesoderm
What do WT-1 & SF-1 do together?
WT-1
What gene helps to establish the bipotential gonad on the genital ridge, regulates expression of SF-1?
SF-1
What gene maintains the early gonads?
Without WT-1: early gonads are not formed
Without SF-1: early gonads are not maintained
What happened to mice in the experiment from class without WT-1? Without SF-1?
The embryo has reproductive tissues can develop into male or female structures
What does the term bipotential embryo mean?
No
Are the gonads bipotential?
Yes
Are the internal genitalia originally bipotential?
SRY is the sex-determining region on the Y chromosome.
It turns on a cascade of genes and goes away
If SRY is present, testes develop.
SRY upregulates SOX-9
What is SRY and what is its role in the sex differentiation pathway?
Sertoli cells
What will SRY expressing cells eventually become?
DNA & SOX9
What are the targets of SRY?
Testes do not develop
What happens if SRY is not present?
Induces Sertoli cell differentiation, upregulates Sertoli cell Anti-Mullerian hormone, and inhibits RSPO1 and WNT4 (ovarian pathway)
It is inhibited by B-catenin.
If it is not present, testes do not develop, and the ovarian pathway is not repressed
What is the role of SOX9 in the sex differentiation pathway? Who inhibits it, who does it inhibit, what does it promote, what happens if it is not present/active?
