5. Sex determination Flashcards
(18 cards)
What appears identical in early development up to 6 weeks in humans?
Male and female gonads
Despite genetic differences, male and female gonads appear identical until the differentiation triggered by the SRY gene.
What gene is responsible for triggering male gonadal development?
SRY gene
The SRY gene is located on the Y chromosome and is crucial for male differentiation.
What is the role of the SRY gene in male development?
Triggers SOX9 expression leading to testis development
The SRY gene initiates a cascade that differentiates the gonads into testes.
What pathway is activated in the absence of the SRY gene?
Female pathway involving WNT4/β-catenin signaling
This pathway leads to ovary development.
Where is the SRY gene located?
Short arm of the Y chromosome
It is specifically expressed in somatic cells of the male genital ridge.
How long does SRY need to be expressed for effective male development?
Approximately 6 hours in mice
SRY functions as a transcription factor during this critical period.
What syndromes are associated with mutations or translocation of the SRY gene?
Swyer syndrome and La Chapelle syndrome
These syndromes result in sex reversal conditions leading to infertility.
What does SOX9 activate in male gonadal development?
FGF9 (Fibroblast Growth Factor 9)
SOX9 is a key transcription factor that maintains male development.
What does Anti-Müllerian Hormone (AMH) do in male development?
Causes regression of Müllerian ducts
This prevents the development of female structures.
What do Wolffian ducts develop into under the influence of testosterone?
Epididymis and vas deferens
Testosterone maintains and stimulates the Wolffian ducts.
What is the default pathway in the absence of SRY?
Female pathway leading to ovary development
WNT4 signaling remains active, leading to the development of female reproductive structures.
What happens to Wolffian ducts in females?
They degenerate
Without testosterone, the male structures regress.
What is the fate of female germ cells by 5 months of pregnancy?
All enter meiosis
Female germ cells are arrested in meiosis I until puberty.
What is the role of retinoic acid in meiosis entry?
Activates Stra8 gene in females
Stra8 is the master switch for meiosis entry, while in males, retinoic acid is degraded.
What is a significant difference between male and female germ cell development?
Males maintain lifelong ability to produce sperm; females have a finite number of eggs
This leads to menopause in females around age 50.
What are possible explanations for menopause in humans?
Energy conservation, grandmother hypothesis, shorter pre-modern lifespan
Menopause is rare in mammals and has several theories regarding its evolution and significance.
What disorders can arise from androgen receptor function loss?
Testis formation with female external phenotype
This highlights the complexities of sex development disorders.
What is the importance of vitamin A during pregnancy?
Required for proper germ cell development
A deficiency could affect retinoic acid signaling and germ cell differentiation.
