Lecture
sexchromosomes the chromosomal theoryof inheritance 11 Ma
sexchromosome
chromosome longstringsofDNAwrappedaround histone proteins
sexchromosome a typeofchromosomeinvolved in sex determination
Humans andmostothermammalshave 2sexchromosomes x andy
thatin combinationdetermine anindividual'ssex
Females xx males xy
autosomes
anychromosomethat's not asexchromosome Nettiestevensdiscoveredsexchromosomes
Human chromosomes malemealwormsproduced 2kindsof sperm onew large chromosome
humanshave 23pairs ofchromosomes 46total andonewi smallchromosome
22pairsof autosomes spermwtlarae wouldproducefemaleoffspringwhenfertilizing eggs
23rdpairis a pairo fsex chromosomes ax orxp spermw small wouldproducemale offspringwhenfertilizingeggs
pairlaterknownas xychromosomes
Human x and y chromosomes
x chromosome 150Mb morethan1000genes
y chromosome somb only sogenes
only 3Mb is homologous between xand y chromosomes s crossingoveroccurs inthissmallregion
Howdidsexchromosomes evolve
x and y chromosomesstarteddiverging 300millionyearsago
x and y chromosomes avewdistinctareto suppressed recombination crossingover inthe Ychromosome
wesuppressed recombinationin 4 thereisalmostno sharingofgeneticmaterial between x and ychromosomes
recombination womanomoanize the sexenromosomes ana
biomostoftheychromosome doesnotundergo recombination
mosto fitsgenes
Iiia iii iii
biomostg enes intheychromosome aredeactivated mostgenesinthe xchromosomehavenohomologousgenesinthe4chromosome
thus recessiveallelesin willbeexpressedin the xygenotype
man chromosomesas a male
Iii
unendctivated
in However thelevelofexpression of xlinkedgenes isabout
the neuromosome
inactivation of one chromosome in xxfemalesenables
similarexpression of genes
doallorganismshavesexchromosomes
nomanyspeciesareasexual somespeciesdifferents exesareenvironmentally
isthemalealwaystheheterogameticsex determined extempstress
havingdifferentsexchromosomes
inheritance of xandy chromosomes
ofthesexchromosomes duringmeiosisin themalegermline
mendeliansegregation
1 ratioofx andycarryingsperm
resultsin
randomfertilizationbetweenmaleand femalegametes resultsin a lil ratio
offemale maleembryos
x linkeddiseasessnowupmoreoftenin malesthan infema
ThomasHuntM organ anvarannmorgan
sS antiatin
chromosomaltheoryof inheritance
Genesarestoredinchromosomesinside
ehheipioiit
YEIthavean unusualc hromosomecomposition
cellnuclei crossingover nondisjunction discovereda
fly w 2attached chromosomes
Drosophiliagenetics discoveredthattherecessivewhiteeyedphenotype reappearedinthe generation
but in 2malesonly
whyonlyin males x linked
sexchromosomes the chromosomal theoryof inheritance 11 Ma
sexchromosome
chromosome longstringsofDNAwrappedaround histone proteins
sexchromosome a typeofchromosomeinvolved in sex determination
Humans andmostothermammalshave 2sexchromosomes x andy
thatin combinationdetermine anindividual'ssex
Females xx males xy
autosomes
anychromosomethat's not asexchromosome Nettiestevensdiscoveredsexchromosomes
Human chromosomes malemealwormsproduced 2kindsof sperm onew large chromosome
humanshave 23pairs ofchromosomes 46total andonewi smallchromosome
22pairsof autosomes spermwtlarae wouldproducefemaleoffspringwhenfertilizing eggs
23rdpairis a pairo fsex chromosomes ax orxp spermw small wouldproducemale offspringwhenfertilizingeggs
pairlaterknownas xychromosomes
Human x and y chromosomes
x chromosome 150Mb morethan1000genes
y chromosome somb only sogenes
only 3Mb is homologous between xand y chromosomes s crossingoveroccurs inthissmallregion
Howdidsexchromosomes evolve
x and y chromosomesstarteddiverging 300millionyearsago
x and y chromosomes avewdistinctareto suppressed recombination crossingover inthe Ychromosome
wesuppressed recombinationin 4 thereisalmostno sharingofgeneticmaterial between x and ychromosomes
recombination womanomoanize the sexenromosomes ana
biomostoftheychromosome doesnotundergo recombination
mosto fitsgenes
Iiia iii iii
biomostg enes intheychromosome aredeactivated mostgenesinthe xchromosomehavenohomologousgenesinthe4chromosome
thus recessiveallelesin willbeexpressedin the xygenotype
man chromosomesas a male
Iii
unendctivated
in However thelevelofexpression of xlinkedgenes isabout
the neuromosome
inactivation of one chromosome in xxfemalesenables
similarexpression of genes
doallorganismshavesexchromosomes
nomanyspeciesareasexual somespeciesdifferents exesareenvironmentally
isthemalealwaystheheterogameticsex determined extempstress
havingdifferentsexchromosomes
inheritance of xandy chromosomes
ofthesexchromosomes duringmeiosisin themalegermline
mendeliansegregation
1 ratioofx andycarryingsperm
resultsin
randomfertilizationbetweenmaleand femalegametes resultsin a lil ratio
offemale maleembryos
x linkeddiseasessnowupmoreoftenin malesthan infema
ThomasHuntM organ anvarannmorgan
sS antiatin
chromosomaltheoryof inheritance
Genesarestoredinchromosomesinside
ehheipioiit
YEIthavean unusualc hromosomecomposition
cellnuclei crossingover nondisjunction discovereda
fly w 2attached chromosomes
Drosophiliagenetics discoveredthattherecessivewhiteeyedphenotype reappearedinthe generation
but in 2malesonly
whyonlyin males x linked
