BIOL 3301 - Genetics Ch3C - Sex-linked St

8/18/2019 BIOL 3301 - Genetics Ch3C - Sex-linked St

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Sex Determination and Genes

Located On Sex Chromosomes• Thomas Morgan, 1910, Drosophila

melanogaster, white eye mtation


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!hite eyes in Drosophila

"#$ %

"#$

"#

&' (emales "!$"!$ red eyes x

males "!% #hite eyes

)1' "!$"!* "!$%, all red

&' (emales "!"! #hite eyes x

males "!$% red eyes

)1' "!$"! red* "!%, #hite

"# %

"#$

"#


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Chromosomal Theory O(

+nheritance• istorical signi(icance -direct e.idence that

genes are located

//////////////////////////////////

• Correlation et#een Mendels #or2 and the

eha.ior o( chromosomes //////////////

• http'33###4dna(t4org3dna(t3103animation3

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Sex Determination• T#o #ays in #hich sex can e determined'

- Environment'• Trtles 5 //////////////////////////

• Some (ish 5 Social strctre

- Chromosomes 5 Three methods'

• "O 5 ///////////////////////// ie ees, haploid males diploid(emales

• 6! 5 ////////////////// 76!8 (emales, homogametic 7668 males, ie

irds

• "% 5 eterogametic 7"%8 males, //////////// 7""8 (emales, ie

hmans and Drosophila


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Sex Determination +n Drosophila

• +n (lies, sex determination is de to an "5chromosome5atosome alance system4

• +( the "5chromosome to atosome ratio is //////////,the (ly is (emale4

• +( the "5chromosome to atosome ratio is ////////,the (ly is male4

• "" (emale (lies 7"':8

• "% male (lies 71"':8

• ""% (emale (lies 7"':8

• "O male (lies 71"':8


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Sex Lin2age in mans

• n ;


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Sex Lin2age in mans

• Sex5lin2ed disorders'

- emophilia

- Color lindness

- )ragile " syndrome, atism

- hereditary nearsightedness

- night lindness

- ichthyosis 7a s2in disease8


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man "5lin2ed @ecessi.e

Genes• Aro#n enamel -

- Tooth enamel appears ro#n rather than #hite

• emophilia 5 T#o types'

- : 5 Classic hemophilia, de(iciency o( lood clotting

(actor B+++

- A 5 Christmas disease, de(iciency o( lood clotting

(actor +"


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"5lin2ed @ecessi.e Genes

@elated to sight

• Colooma iridis 5 : (issre in the eyes iris

• Color Alindness 5 T#o types'

- Detan 5 Decreased sensiti.ity to green light - &rotan 5 Decreased sensiti.ity to red light

• Congenital night lindness 5 ot de to a de(iciency o(

.itamin :

• Microphthalmia 5 yes (ail to de.elop

• Optic atrophy 5 Degeneration o( the optic ner.es


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• +( a sex5lin2ed trait is de to a recessi.e allele, a

(emale ha.e this phenotype only i(

////////////////////////////////// - etero>ygos (emales #ill e /////////////////

• Aecase males ha.e only one " chromosome

7hemizygous8, any male recei.ing the recessi.eallele (rom his mother #ill

//////////////////////////////////////

• Males are (ar more li2ely to inherit sex5lin2edrecessi.e disorders than are (emales4

Copyright© 2002 Pearson Education, Inc., publishing as Benjamin Cummings


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emophilia

• emophilia is a grop o( diseases #hen

lood do not //////////////////

• )actors in lood are in.ol.ed in clotting4

emophiliacs lac2ing the normal (actor

B+++ are said to ha.e hemophilia :, the

most common (orm


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• Duchenne muscular dystrophy a((ects one in

E,F00 males orn in the nited States4 - :((ected indi.idals rarely li.e past their early 0s4

- This disorder is de to the loss o( (nction o( an "5

lin2ed gene (or a 2ey mscle protein, called /////////////////////////////////////

- The disease is characteri>ed y a progressi.e

#ea2ening o( the mscles and loss o( coordination4



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Fragile X Syndrome

: oy #ith (ragile " syndrome4 ote the prominent and elongated

ears and long (ace4 Children (rom di((erent ethnic grops ha.e

similar characteristics4 This occrs in aot 1 in 1F00 males4

:((ected (emale carriers are typically normal4 Most o( the a((ected

males ha.e mental retardation4


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Chromosome X

Contains o.er 1


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Chromosome Y

•Contains o.er 00 genes•Contains o.er F0 million ase pairs, o( #hich approximately F0H

ha.e een determined


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%5lin2ed +nheritance

• S@%

• airy ears


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The @atio o( Males to )emales

in mans" %

"

"


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Dosage Compensation &re.entsxcessi.e xpression o( "5Lin2ed

Genes in Mammals

Aarr Aodies


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• :lthogh (emale mammals inherit t#o "

chromosomes, only

/////////////////////////////////// • There(ore, males and (emales ha.e the same

e((ecti.e dose 7one copy 8 o( genes on the "

chromosome4 - Dring (emale de.elopment, one " chromosome per

cell condenses into a compact oIect,

////////////////////////////////////

- This inacti.ates most o( its genes4



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• " inacti.ation in.ol.es the attachment o( methyl

7CE8 grops to cytosine ncleotides on the "

chromosome that #ill ecome the Aarr ody4• One o( the t#o " chromosomes has

////////////// XIST gene 7"5inacti.e speci(ic

transcript84


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• The orange and lac2 pattern on tortoiseshell

cats is de to patches o( cells expressing an

orange allele #hile others ha.e a non5orangeallele4


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• xpression o( genes that are not necessarily on the

" chromosome may e in(lenced /////////////////////// o( the indi.idal

• One maIor reason (or this is the impact that steroid

sex hormones ha.e on the expression o( genes• //////////////////////////

Sex5+n(lenced Or Limited Genes

Genotype Phenotype

Female Male

BB Bald Bald

Bb Flocculent Bald

bb Flocculent Flocculent


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&rolems

• http'33###42s4ed3iology3po3genetics3xl

in2ed4htm

BIOL 3301 - Genetics Ch3C - Sex-linked St

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