BIOL1008 Lecture Notes - Lecture 10: Scrotum, Congenital Adrenal Hyperplasia, Heterogametic Sex
Gender Determination
Gender assignment
Chromosomal makeup- XX or XY
Internal organs- testes or ovaries
External genitalia- penis or vagina
Gender assignment needs to take into account all three aspects
Chromosomal Makeup
Packing of genes
Typical human: 46 XX or 46 XY
Human males are the heterogametic sex with two different sex chromosomes (XY)
Human females are the homogametic sex (XX)
In other species sex determination differs e.g. birds, parthenogenesis in komodo
dragons)
Stages in reproductive development
Formation or urogenital ridge (tissue that will develop into testes or ovaries)
Gonad formation- testes or ovaries- determined by presence and activity of SRY gene
Sex determination- typically occurs as a consequence of gonad formation
Sex differentiation- recognising how the sexes are phenotypically differentiated
Pre-requisites for usual sex development
Intact chromosome complement
Fully functioning sex determination genes
Intact steroid hormone pathway
Default development option is female
Disorders of Sex Development (DSD)- Intersex conditions
Maleness is something that is imposed on the neural female state by secretion of
androgens (testosterone)- gender isn’t just determined by chromosomes, hormones
are also very important
1 in 500 people have a chromosomal disorder
Chromosomally related differences
oTurner Syndrome
45 X or XO (only affects females)
Approx. 1 in 2000 girls in Australia
Monosomy: not inherited
SHOX gene (on X chromosome) important for bone development and
growth- results in short stature
Rarely fertile
oKlinefelter Syndrome
47 XXY (only affects males)
Approx. 1 in 500-1000 in Australia
Fairly common
find more resources at oneclass.com
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Document Summary
Gender assignment needs to take into account all three aspects. Human males are the heterogametic sex with two different sex chromosomes (xy) Human females are the homogametic sex (xx) In other species sex determination differs e. g. birds, parthenogenesis in komodo dragons) Formation or urogenital ridge (tissue that will develop into testes or ovaries) Gonad formation- testes or ovaries- determined by presence and activity of sry gene. Sex determination- typically occurs as a consequence of gonad formation. Sex differentiation- recognising how the sexes are phenotypically differentiated. Maleness is something that is imposed on the neural female state by secretion of androgens (testosterone)- gender isn"t just determined by chromosomes, hormones are also very important. 1 in 500 people have a chromosomal disorder. Shox gene (on x chromosome) important for bone development and growth- results in short stature. Androgen (testosterone) related: androgen insensitivity syndrome (ais) 1:13,000. Neither testosterone nor dihydrotestosterone (dht- most active form) can bind to receptors.
