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  #1  
Old 07-18-2012
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Default X linked

the boy with fragile X syndrome Two maternal uncles have mental
retardation. The patient comes from a family of
four daughters. If the parents appear healthy, on
average how many of their daughters are most
likely carriers of this gene mutation? Please explain your answer. Thank you!
(A) 0
(B) 1
(C) 2
(D) 3
(E) 4

Last edited by eveli55; 07-18-2012 at 09:48 AM.
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  #2  
Old 07-18-2012
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i got it


An affected woman passes the condition to every son and half her
daughters
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  #3  
Old 07-18-2012
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(A) 0
Fragile X is a X- dominant disease.... No carriers in dominant diseases...
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  #4  
Old 07-18-2012
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Quote:
Originally Posted by sanjitt View Post
(A) 0
Fragile X is a X- dominant disease.... No carriers in dominant diseases...
X-linked dominant disorders
Rules
1 The condition is expressed and transmitted by both sexes.
2 The condition occurs twice as frequently in females as in males.
3 An affected man passes the condition to every daughter, but never
to a son.
4 An affected woman passes the condition to every son and half her
daughters.
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  #5  
Old 07-18-2012
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i'm so sorry but golgan says fragile x syndrome is x-linked recessive disorder not x-linked dominant if recessive:
affected male XY transmit the mutant gene to all of their daughters
males are homozygous for the mutant gene ,example XY x XX ---XX,XX,XY,XY, daughters are asymptomatic carriers XX
asymptomatic female carriers transmit the disorder to 50% of their male offspring .example XX x XY---XX,XX,XY,XY
offspring of a symptomatic male and asymptomatic female carier:
XX x XY---XX,XX,XY,XY
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  #6  
Old 07-18-2012
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Quote:
Originally Posted by irakly View Post
i'm so sorry but golgan says fragile x syndrome is x-linked recessive disorder not x-linked dominant if recessive:
affected male XY transmit the mutant gene to all of their daughters
males are homozygous for the mutant gene ,example XY x XX ---XX,XX,XY,XY, daughters are asymptomatic carriers XX
asymptomatic female carriers transmit the disorder to 50% of their male offspring .example XX x XY---XX,XX,XY,XY
offspring of a symptomatic male and asymptomatic female carier:
XX x XY---XX,XX,XY,XY
Wt u said is right..kalpan notes mentioned it as X- dominant..
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  #7  
Old 07-18-2012
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yes ,i know so whic one is correct?
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  #8  
Old 07-18-2012
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Quote:
Originally Posted by eveli55 View Post
X-linked dominant disorders
Rules
1 The condition is expressed and transmitted by both sexes.
2 The condition occurs twice as frequently in females as in males.
3 An affected man passes the condition to every daughter, but never
to a son.
4 An affected woman passes the condition to every son and half her
daughters.
i don't understand rule 4, because normal male -heterozygous affected female:50% sons and 50% daughters will be affected
XY x XX---XX,XX,XY,XY
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  #9  
Old 07-18-2012
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[QUOTE=irakly;133777]i don't understand rule 4, because normal male -heterozygous affected female:50% sons and 50% daughters will be affected
XY x XX---XX,XX,XY,XY[/
Same doubt here...
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  #10  
Old 07-18-2012
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Quote:
Originally Posted by irakly View Post
yes ,i know so whic one is correct?
May b both X-dominant & X- resessive exist...
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  #11  
Old 07-19-2012
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Quote:
Originally Posted by irakly View Post
i don't understand rule 4, because normal male -heterozygous affected female:50% sons and 50% daughters will be affected
XY x XX---XX,XX,XY,XY
I can recomend you nice book - medical genetics at a glance
This book is most useful for me.
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  #12  
Old 07-19-2012
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Quote:
Originally Posted by eveli55 View Post
I can recomend you nice book - medical genetics at a glance
This book is most useful for me.
i have checked kaplan ln and found same one-normal male-affected woman in x-linked dominant diseases-50% sons and 50%daughters will be affected
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  #13  
Old 07-19-2012
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Quote:
Originally Posted by irakly View Post
i have checked kaplan ln and found same one-normal male-affected woman in x-linked dominant diseases-50% sons and 50%daughters will be affected
Great!!!!!!
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