Sex determination pathways 6.3 Flashcards
ZZ vs ZW sex determination
ZZ= male (homogametic)
ZW= female (heterogametic)
Ex: birds
XO sex determination
O signifies the absence of a sex chromosome
Females: XX
Males: XO
Haplodiploidy
Males are haploid
Females are diploids
Ex: honeybees
Genic mating systems
A single gene determines mating types in some organisms. The alleles of that gene determines sex (mating type)
Hermaphroditism: both males and females
C. Elegans: self-fertile females (hermaphrodites acting as male and female for reproduction) Males are rarely produced through NDJ, females will preferentially mate given the choice
simultaneous hermaphrodites
individuals have both male and female reproductive organs
during mating rituals, a pair takes turn acting as male and as female for multiple matings
Example: hamlets
Sequential hermaphrodites
Switch between male and female
The largest fish in the shool is female, all others are male
If something happens to the female, the largest male turns into female
example: clownfish
Environmental sex determination
Cold temperature –> certain gender
Warm temperature –> certain gender
Autosome balance determine systems
The Y chromosome does not determine sex
The ratio of X to autosomes (X:A) determines the expression of Sxl, a gene that signals the female sex determination pathway
When does the development of sex characterisitcs begin?
7 weeks
DSD
Differences in sex development (intersex)
Umbrella term to described conditions where individuals have sex characterisitcs that do not fit the typical definition for male or female bodies
–># and type of sex chromosomes
–> gonads
–> sex hormone levels
–> internal reproductive anatomy
–> external genitalia
Androgen insensitivty syndrome (AIS)
a hormone receptor is encoded by a gene on the X-chromsome. XY individuals with a mutation in this gene develop external female fenitalia (and usually lack a uterus)
Typically do not respond to high testosterone levels
Mutations in the Y-linked SRY gene can also lead to complete or partial development of female sex characteristics
Rarely, are they fertile
5-alpha reductase deficiency
XY karotypes; autosomal recessive mutation that blocks production of DHT (testosterone precursor)
Typically do not develop male genitalia
Hormone increases during puberty can activate development pathways
Congenital adrenal hyperplasia
Genetic variants in autosomal genes can alter adrenal gland hormone production.
XX-CAh individuals typically have high testosterone levels
Can present as typical female, typical male or ambiguous sex characterisitcs
Typically produce high levels of testosterone.
Typically male characteristics, are very short and experience early puberty
