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SEX DETERMINATION & SEX-LINKED CHARACTERISTICS (XY sex determining…
SEX DETERMINATION & SEX-LINKED CHARACTERISTICS
Sex determining systems
Most organisms have 2 sexes MALE or FEMALE
determined by :one:chromosomes :two:genes :three:environment
there are :one:two different sex chromosomes but rather determined sex by :two:genes located on sex chromosomes
:three: Nutrition and Heat BUT sex ratio in human is 1:1 (heterozygous female x homozygous male) :arrow_right: sex determination is resistant to environment factor
XY sex determining systems
gives 1:1 ratio of sex
Female needs 2 X chromosomes
Male needs 1 X chromosome
sex chromosome aneuploidy
comparing human phenotype and mouse phenotype :arrow_right:
suggesting that sex is determined as male when Y chromosome is present
:!!: Turner's Syndrome (XO) and Klinefelter's Syndrome (XXY) conclude that Y carries some genes (:two:) required for
male sex determination
:warning:X and Y chromosomes in human are different in size and shape
Homologous
only in the
pseudoautosomal region
:arrow_right: able to match for
crossover
:arrow_right: may get mutation
Human Sex Differentiation
Mamalian sex determination
Factor responsible for initiating testis formation is Testis-determining factor (TDF) a.k.a sex-determining gene (SRY) :arrow_forward:
SRY protein is transcription factor
:arrow_right: stimulating the transcription of other genes :arrow_right: promote the development of testes
SRY gene
is close to pseudoautosomal region :arrow_right: Crossing over may occur at here as well (
translocation
) :arrow_right: may cause abnormality
:check: SOX-9 cooperates with other genes to activate the expression of Anti-Mullerian Hormone :arrow_right: SOX-9 upregulated in male
Dosage compensation
in embryonic cell, X chromosome is randomly inactivated (because there are 2 X chromosomes)
Inactivated X chromosome is Barr body
It is densely stained objects in the nuclei of females
most Barr body genes are not expressed :arrow_right: able to avoid the mutation phenotype at here
It is reactivated to give rise the Ova
XIST
gene ( X-inactive specific transcript) becomes active on the chromosome that will become the Barr body
multiple RNA attach to the X-chromosome :arrow_right: interaction of RNA and chromosome initiates INACTIVATION
