Sex Determination
• Chromosomal Sex Determination
• Primary and Secondary Sex Determination
• Another model of chromosomal sex determination:
Drosophila
• Environmental Regulation of Sex Determination
Mammalian Sex Chromosomes
• Formation of bipotential
gonad.
• Males= XY
• Females= XX
• Sex determined by Y
chromosome- SRY gene
Bipotential Gonad Formation
• Intermediate Mesoderm
• Mesonephric tubules
Bipotential Gonad Formation
• Intermediate Mesoderm
• Mesonephric tubules
WT1
Wnt4
SF1
Sox9
FGF9
GATA4
Bipotential Gonad Formation
• Intermediate Mesoderm
• Mesonephric tubules
• Formation of Sex specific
gonads
Bipotential Gonad Formation
• Intermediate Mesoderm
• Mesonephric tubules
• Formation of Sex specific
gonads
• Reorganization of ducts
Figure 14.3
SRY Gene
• Only on Y Chromosome
• Upregulates Sox9
Boy or Girl?
Chromosomes: XX
Wnt4, R-spo1
Bipotential
Gonad
b-catenin
Sox9
Ovary
Boy or Girl?
Chromosomes: XY
Sry, Sf1
Bipotential
Gonad
Anti Mullerian Factor (AMF)
Fgf9
Sf1
Sox9
Testes
b-catenin
Sox9: Autosomal Testis-determination gene
Secondary Sex Characteristics: Females
• Estrogen
• Fig. 14.3
Secondary Sex Characteristics
Male Phenotype: Testosterone and AMF
• AMF: blocks development of Müllerian Tube
• Testosterone and dihydrotestosterone
Genetics of Secondary Sex determination
• Hermaphrodites: Having
secondary sex
characteristics for both
genders
• Androgen Insensitivity
Syndrome
• Chromosomal Translocation
of SRY
• Pseudohermaphroditism
• Congenital Adrenal
Hyperplasia
Caster Semenya
Sex on the Brain
• SRY and the brain
• Aromatase
• Gyandromorphs: Some
body parts male, some
female
• Bird Gyandromorphs
Sex on the Brain
• Most Mammals, estrogen
(estradiol) masculinizes the
brain
• a-Fetoprotein
• Prostaglandin E2 (PGE2)growth of areas in male
brain involved in sexual
behavior (hypothalmus,
limbic system)
Drosophila Sex Determination
• XX/XY
• Previously called X:A
ratio
• Sex-Lethal (Sxl)
Sxl Dosage and Sex Determination
RNA splicing and Sex Determination
Fruitless: Mating Behavior
Environmental Sex Determination
• Temperature
• Location, Location,
Location
Temperature and Reptiles
Temperature and Estrogen
Environment and Sex Determination: Atrazine
• Polychlorinated biphenyl
compounds (PCBs) act as
estrogens
• Atrazine: Weed killer
• As low as 0.1 ppb can have
gonadal/sexual anomalies in male
frogs.
PCBs
– U.S. Drinking water= 3 ppb
– Midwestern water = ~224 ppb
• Hayes et al (2002) found that 7 of
8 sites in Midwest contain
Atrazine.
• Atrazine upregulates Aromatase
Atrazine
Location