MALE SEX DETERMINATION PAX 2 EMX2 INSR, IGF1R SEI GATA4 /FOG2 IRR, POD1 DAXI? me
ID: 272511 • Letter: M
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MALE SEX DETERMINATION PAX 2 EMX2 INSR, IGF1R SEI GATA4 /FOG2 IRR, POD1 DAXI? mesoderm DAKI WNT4 RS#01 Vanin-1, Nexin-1 FONLZ Sertoli cell TESTIS Ro Leydig cell Part of the HUMAN sex determination pathway is shown above. For A-D, circle the statements that are true and correct the statements that are false. Arrows between genes indicates activation, -l indicate repression. A. Men do not have dosage compensation. B. In X0 and XXX women, the X:A ratio are 1:1 and 3:1, respectively. C. XX human males can arise from non-disjunction during meiosis. D. XYY humans show no dosage compensation. E. Four brothers in a family were found to be 46, XX, sry-; there was no trace of the Y chromosome (including sry) anywhere in their genomes. There are also no mutations in the promoter, repressorlenhancer elements, or coding region of the Sox9 gene. In ONE sentence, suggest where a mutation has occurred in the sex determination pathway to give rise to the four 46, XX, sry- brothers. F. Suppose that there is a RARE case of a fertile 46, XX, sryt male. In ONE sentence, what will be the sex and genotype of the children this male can have?Explanation / Answer
A. True
Dosage compensation is a biological process by which an organism maintains expression of genes between members of different biological sexes. Dosage compensation is occurred in female, having XX chromosomes. Here one of the X chromosome become inactivated to maintain or equalise the expression in female. It is not occurred in human males because males have only one X chromosome and one Y chromosome.
B. False
The X: A ration is, the ration of X chromosome to set of Autosomal chromosomes. Humans have 2 set of autosomal chromosomes.
Here normal female has 2 X chromosomes. Hence the ration is 2X: 2A which means 1:1 or 1.0. In male one X chromosome is present hence the ration is 1X: 2A which means 1:2 or 0.50. Here Y chromosome is not consider in calculation. Same case is with X0 female, 1X: 2A means 1:2 or 0.50.
In case of XXX female 3X: 2A is the possible ration. So the ration is 3:2 or 1.50.
C. False
In non disjunction the pair of the homologous chromosome is unable to separate equally Which results in ploidy. For example XXY male. But XX male is originated due to translocation of some of the SRY gene region of Y chromosome to the X. It is not arise due to non disjunction.
D. True.
Dosage compensation is occurred due to the inactivation of extra chromosome and it is observed in XX female. No evidence of Y chromosome inactivation is till date reported. Hence dosage compensation is not possible in XYY and generally the XYY males are normal or nearly normal.
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