Sex Determination Flashcards
What, on the Y chromosome, results in development of male phenotype?
Testis determining factor: SRY gene
At what stage of development can gender still not be determined?
From fertilisation up to 7 weeks of embryonic development
An early embryo for which gender has not yet been determined can be described as what?
Bipotent or sexually indifferent
What part of the embryo develops into the testes/ovaries?
Gonadal ridges
What are the reproductive ducts found in:
A) males?
B) females?
A) Wolffian duct
B) Müllerian duct
It was long thought that female sexual development was simply the default position in the absence of the SRY gene - but what is also needed?
The presence of two X chromosomes
Name the genes involved in the conversion of the bipotential gonad into:
A) ovaries?
B) testes?
A) DAX1 and WNT4a
B) SRY and SOX9
The Wolffian duct results in the male internal genitalia. What are they?
- Epididymis
- Vas deferens
- Seminal vesicle
The Mullerian duct results in the female internal genitalia. What are they?
- Uterus
- Oviduct
- Cervix
- Upper vagina
What are the three major things needed for normal sexual development?
- Presence of normal sex chromosome complement
- Correct function of many genes within the sex chromosome complement
- Correct response of hormone receptors
What is sex reversal?
When the phenotypic sex and chromosomal sex differ
- e.g. Male phenotype with a female Karyotype
What are the two ways in which you can get a male phenotype with a female Karyotype?
- Small segment of Y chromosome material, including SRY, in the place of distal part of one X chromosome (=80%)
- No SRY and partial male/ambiguous sexual development (=20%)
What are the two ways in which sex reversal occurs in XY females?
- Swyer syndrome: genetic mutation in either SRY or another gene in male sex determination cascade
- Patients with androgen insensitivity syndromes who have normal SRY gene function but have failure of response to an androgen receptor
What is Swyer syndrome also known as?
Pure gonadal dysgenesis (streak gonads)
What are patients with Swyer syndrome at high risk of developing?
Gonadoblastoma (30%) - removal of gonads in first decade of life recommended
What are the clinical features of Swyer syndrome?
- streak gonads
- female external genitalia
- failure of pubertal development
- infertility
- high risk of gonadoblastoma
What is complete androgen insensitivity also known as?
Testicular feminisation
What are the clinical features of complete androgen insensitivity?
- female external genitalia, short/absent vagina
- normal pubertal development of breasts and female characteristics
- amenorrhoea (absence of periods)
- infertility
- intraabdominal testes
- low risk of Gonadoblastoma
What is the cause of androgen resistance syndromes?
Very rare enzyme defects: e.g. 5alpha reductase or 17alpha hydrolase deficiency
What condition do enzyme deficiencies affecting steroidogenesis cause?
Congenital Adrenal Hyperplasia (CAH)
What are the key details for classic congenital adrenal hyperplasia?
- e.g. 21-hydroxylase deficiency
- XX Karyotype = masculisation of external genitalia of female fetus, XY Karyotype = normal genitalia
- treat during pregnancy with dexamethasone and after birth with hormones
- both sexes if left untreated = salt wasters. Can lead to death in first few weeks of life
How does autosomal sex reversal occur?
XY Karyotype with autosomal imbalance in regions carrying other genes in male determining cascade
What is the definition of a true haemaphrodite?
- Gonads comprise both ovarian and testicular elements
- Have ambiguous external genitalia
- most commonly 46XX with no Y chromosome
What is the difference between a female and male pseudohermaphrodite?
They have ambiguous genitalia and gonads comprising of either ovarian elements only (female) or testicular elements only (male)
