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BIOL 202 Study Guide - Coagulopathy, Haemophilia B, Genetic Counseling


Department
Biology (Sci)
Course Code
BIOL 202
Professor
David Hipfner

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Biol-202 week-1 Conferences (Winter-2014)
!
!"#!Hemophilia!B!is!a!rare!blood!clotting!disorder!caused!by!mutation!in!a!single!
gene!(factor!IX)!located!on!X;chromosome.!The!gene!shows!a!classical!sex;linked!
recessive!inheritance.!Half!of!Michael!and!Melanie’s!children!(2!boys)!suffer!from!
hemophilia!B.!However,!neither!the!couple!nor!couple’s!parents!are!affected.!Based!
on!this!information,!which!of!the!following!statements!is!true?!!
!
A.!Michael’s!mother!is!a!carrier!for!the!trait.!
B.!Melanie’s!father!is!a!carrier!for!the!trait.!
C.!Melanie’s!mother!is!a!carrier!for!the!trait.!!
D.!Michael’s!father!is!a!carrier!for!the!trait.!!
!
!$#!A!phenotypically!normal!female!is!heterozygous!for!a!rare!autosomal!recessive!
Mendelian!allele!causing!phenylketonuria,!a!disease!caused!by!inability!to!convert!
amino!acid!phenylalanine!to!tyrosine.!The!same!female!is!also!heterozygous!for!a!
recessive!X;linked!allele!causing!red;green!blindness.!What!percentage!of!her!eggs!
will!carry!recessive!allele!for!at!least!one!of!the!diseases?!
!
%&!Rosalind!(age!23)!and!Gregor!(age!27)!are!expecting!a!baby!but!they!are!worried!
by!the!medical!history!of!Rosalind’s!family.!You!are!genetic!counsellors!and!would!
like!to!help!them!understand!their!situation.!You!find!out!that!although!many!of!her!
relatives!thrive!as!young!adults,!several!have!succumbed!to!cognitive!decline!and!
psychiatric!problems!in!their!mid;adult!lives!(35!to!45!years).!Rosalind!knows!that!
her!mother!and!maternal!grandfather!both!developed!the!disorder.!In!contrast!
Rosalind’s!maternal!grandmother,!maternal!aunt,!her!father,!her!paternal!uncle,!and!
her!paternal!grandparents!lived!with!good!cognitive!health!into!their!old!age.!
Rosalind!also!knows!that!the!disorder!is!rare!and!has!a!simple!(1!gene)!basis.!
Unfortunately,!her!family!refuses!to!give!her!any!other!information.!!
!
!# Draw!a!pedigree!for!Rosalind’s!family.!
%# What!is!likely!the!genetic!basis!of!this!disorder?!
'# What!is!the!probability!that:!
a. Rosalind!will!have!the!disorder?!
b. Their!baby!will!have!this!disorder?!
(# What!neurogenerative!disorder!could!this!be?!(you!don’t!have!to!know!this)!
!
!
'&!You!are!in!charge!of!the!breeding!program!of!an!endangered!species.!Below!is!the!
family!tree!of!a!group!of!individuals!in!the!population.!Some!offspring!are!affected!
by!a!fatal!genetic!disorder.!
!
"#!How!is!this!genetic!disorder!inherited?!
$#!Which!individuals!from!this!entire!tree!should!be!removed!from!the!breeding!
pool!to!prevent!this!disorder!from!being!passed!on?!

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!
!
!
(&)You!are!a!graduate!student!working!in!TH!Morgan’s!lab.!After!two!years!of!
breeding!flies,!you!identify!a!spontaneous!new!mutant!with!a!red!symbol!on!its!
chest.You!are!currently!living!in!a!time!frame!where!it!has!been!recently!discovered!
that!males!and!females!each!donate!a!haploid!genome!composed!of!chromosomes!to!
the!developing!embryo.!It!has!also!been!recently!posited!that!these!chromosomes!
contain!the!phenotypic!units!that!Mendel!had!discovered!and!their!segregation!
explains!the!various!ratios!that!had!been!previously!observed.!The!nature!of!sex!
chromosomes!was!also!known.!If!you!took!this!mutant!fly!in!1914!and!performed!
controlled!crosses!with!it,!how!would!you!have!explained!each!of!the!following!
observations?!
)
"#!A!cross!between!a!male!symbol!fly!and!a!true!breeding!WT!female!fly!results!in!an!
F1!that!is!50%!symbol!and!50%!wild!type!(both!sexes).!The!F2!cross!between!two!
symbol!flies!(male!and!female)!results!in!25%!embryonic!death,!50%!symbol!and!
25%!wild!type.!
!
$#!A!cross!between!a!symbol!female!and!a!true!breeding!normal!male!result!in!an!F1!
that!is!100%!normal!offspring.!The!F1!cross!results!in!a!3:1!ratio!of!normal!:!symbol!
(both!sexes)!in!the!F2.!!
!
*#!A!cross!between!a!symboled!male!and!a!randomly!picked!normal!female!whose!
background!is!unknown!produces!offspring!that!are!50%!symbol!and!50%!wild!type!
(both!sexes).!There!is!no!time!to!perform!an!F2!cross.!
!
+#!A!cross!between!a!symbol!male!and!pure!breeding!wild!type!female!results!in!an!
all!normal!F1.!The!F2!cross!between!a!wild!type!male!and!a!wild!type!female!result!
in!an!F2!that!is!50%!symbol!male,!and!all!normal!females.!
!
,#!A!cross!between!a!WT!male!and!the!originally!discovered!spontaneous!mutant!fly!
(a!symboled!female)!result!in!an!F1!that!is!100%!symbol!,!however!with!a!symbol!
that!is!smaller!than!the!original!female!from!the!F0!generation!and!is!not!as!brightly!
coloured!red.!The!F1!symboled!flies!are!then!crossed!to!true!breeding!WT!flies!to!
produce!an!F2!that!again!all!have!symbols,!however!they!are!now!barely!visible!
compared!to!even!the!F1!generation.!!
!

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-./0,1/)2341)5-)+6/716$8764.#)
1a)!Answer!is!C.!
b)!Wild!type!(normal)!phenylketonuria!allele!=!P!and!mutant!allele!=!p!
Wild!type!(normal)!red;green!allele!=!C!and!mutant!allele!=!c!
Female’s!genotype=!PpCc!
Since!one!gene!is!located!on!autosome!&!other!on!X!chromosome,!they!will!assort!
independently.!
Gametes;!PC,!Pc,!pC!and!pc!(all!with!equal!probability!of!1/4th!or!25%)!
The!answer!is!3/4th!(or!75%)!
!
2.!!
1)!!
!
!
!
2)!Autosomal!dominant!
3)!a)!½!b)!¼!(½!x!½)!
4)!Huntington’s!disease!(could!be!others!too!that!I!don’t!know!about)!
!
3a)!Autosomal!recessive!
b)!Circled!individuals!are!carriers!and!should!be!removed,!afflicted!are!aa.!
!
!
!
!
!
4a)!Symbol!is!dominant,!homozygous!dominant!results!in!embryonic!lethality.!
b)!Symbol!is!recessive.!
c)!More!crosses!required!to!determine!this!with!absolute!certainty!given!that!we!don’t!
know!the!genetic!background!of!the!female.!Symbol!could!be!dominant!and!the!female!could!
homozygous!WT!while!the!male!is!heterozygous.!Symbol!could!be!recessive!and!the!female!
could!be!a!carrier.!
d)!Symbol!is!sex!linked!recessive.!
e)!This!result!would!have!turned!the!chromosome!theory!of!inheritance!upside!down.!It!
would!look!like!blending!inheritance!(a!debunked!theory!that!existed!at!the!time).!This!
couldn’t!really!be!explained!by!quantitative!or!polygenic!inheritance!as!the!large!bright!red!
original!mutant!appeared!spontaneously!after!years!of!mating.!This!result!was!never!
observed!with!spontaneous!mutants!because!it!isn’t!consistent!with!genetic!transmission.!
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