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Today's X and Y chromosomes weren't sex chromosomes in our ancestor--they were structural and

genetic homologs. Now the Y chromosome contains very few genes, why?Females do not have Y-linked genes, which mean they would be at a disadvantage since they

wouldn't have accessed to some of the phenotypes/ traits that the males have.

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ExtensionstoMendel

Todaysquestion:

Mendel

was

not

aware

of

linkage.

Whatotherpatternsofinheritanceoccurthathe

didntdescribe?

I. Geneticrecombination

II. Linkagemapping

III. Codominance

IV. Genexgeneandgenexenvironment

interactions

V. Pleiotropy,multipleallelism,etc.

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I.Thediscoveryofgeneticrecombination

organ s rs crossw n e genes

XY =normal

body

color;

Xy =

yellow

body

color

Parentalgenotypes: XwY XwY x XWyY

F1 females: F1 males:

LetF1s

mate.

W at

are

t e

genotypes

an

p enotypes

o

F2 MALEoffspring?

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Whatarethegenotypesoftheweirdmales?

Crossingoverasaphysicalmechanismforgenetic

recombination.

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.

Sturtevantsinsight:Thepercentageofrecombinantsis

ro ortionaltothe h sicaldistancebetween enes.

Yellowisat0

e owan w teeye: . recom nants

Yellowand

sable

body:

43%

recombinants

a ean w eeye .

Crossveinless wings and sable: 29.3% recombinants.

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.

AlloftheallelesthatMendelanalyzedwerecompletely

dominantorcom letel recessivewithres ecttoeach

other.

oo ypes n umans

IA allele:GlycoproteinAonredbloodcellsB

iallele:nogeneproductonredbloodcells

IAIA andIAi A

blood

type

IBIB andIBi Bbloodtype

I I ABbloodtype

ii Oblood

type

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III.Genexgeneandgenexenvironmentinteractions

Implicationsfor

inheritance:

When

studying

the

effects

ofagene,youneedtocontrolforgeneticbackground

(othergenespresent)andthephysicalenvironment.

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Case1:InuitresidentsofBarrow,Alaska,wherepeople

over35hadnotattendedAmericanstyleschools.

Age %diagnosedmyopic(samplesize)

3688

Statewhetherthesedataareevidenceofagenexgene

oragenexenvironmentinteraction.Explainyourlogic.

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:

y,

x

sw USAareindistinguishable.

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Assumethatiftheblacklinesondifferentbarsdonot

overlap,itindicatesstatisticallysignificantdifferences.

1.Explain

what

the

data

in

the

left

graph

mean.

2.Explainwhatthedataintherightgraphmean.

3.Someresearcherssuggestthatthereisaconnection

betweenthetwographs.Statethisasahypothesis.

4.Statewhetherthesedataindicateagenexgeneora

, . .