!Objectives!for!Exam !2 !P C B !3 0 6 3 ,!F a ll!20 1 2 !!DR.!BATES!!Chromosome!Abnormalities!(Chapter!6)!!!Q:#Know#the#following#terms#and#their#significance:##Chromosome!mutations!or!chromosome!abnormalities!5#change#in#total###of#chromosomes,#the#deletion#or#duplication#of#genes#or#segments#of#a#chromosome,#and#rearrangements#of#the#genetic#material#either#within#or#among#chromosomes.#PASSED#TO#OFF#SPRING#!Nondisjunction5#leads#to#monosomy#and#trisomy;#where#paired#homologs#fail#to#separate#during#segregation.#ABNORMAL#DISTRIBUTION#OF#CHROMOSOMES##Aneuploidy5#general#condition#where#an#organism#loses#or#gains#one#or#more#chromosomes,#but#not#a#complete#set.#2n#+#or#–#X#chromosome(s)#Monosomy5#loss#of#one#chromosome;#monosomy#for#the#X#chromosome#occurs#in#humans,#monosomy#for#any#of#the#autosomes#is#usually#not#viable.#2n#5#1#ex:#Turner#syndrome#45,#X##Trisomy5#addition#of#an#extra#chromosome#produces#more#viable#individuals#in#animal#and#plant#species#than#does#the#loss#of#a#chromosome.#2n#+#1!!Down!Syndrome,!trisomy!215#the#only#human#trisomy#(autosomal)#in#which#a#significant#number#of#individuals#can#survive#longer#than#a#year.#The#frequency#of#Down#syndrome#is#related#to#the#mothers#age##!Amniocentesis5#(chorionic#villus#sampling)#fetal#cells#are#obtained#from#the#amniotic#fluid#or#the#chorion#of#the#placenta;#after#the#cells#are#obtained,#the#karyotype#can#be#determined.##!Triploid5#three#sets#of#chromosomes#are#present#(3n)#Tetraploid5#four#sets#of#chromosomes#present#(4n)#Polyploid5#multiple#chromosome#sets.#Rare#in#humans,#but#occurs#in#amphibians#and#lower#animals.!!Chromosome!deletion5#chromosome#or#sequence#of#DNA#is#missing.#Duplication5#when#any#part#of#the#genetic#material#(a#single#locus#or#a#large#piece#of#a#chromosome)#is#present#more#than#once#in#the#genome##Inversions5#rearrangement#in#where#a#segment#of#a#chromosome#is#reversed#end#to#end#(180#degrees).##Results#in#a#loss#of#genetic#material,#but#simply#rearranges#the#linear#gene#sequence##Translocations!5#Rearrangement#of#parts#between#non5homologous#chromosomes.##!Q:#Important#Concepts:#Understand#how#nondisjunction#in#meiosis#leads#to#monosomy#and#trisomy,#and#be#able#to#explain#why#essentially#the#only#monosomies#and#trisomies#observed#in#humans#involve#chromosomes#X,#Y,#and#21.!Know!that!Klinefelter!syndrome!is!more!frequent!than!Turner!syndrome!and!why.###5#Nondisjunction#during#the#first#and#second#meiotic#divisions,#some#of#the#gametes#that#are#formed#either#contain#two#members#of#a#specific#chromosome#or#lack#that#chromosome.#After#fertilization#by#a#gamete#with#a#normal#haploid#content,#monosomic,#disomic#(normal),#or#trisomic#zygotes#are#produced.###- The#only#monosomies#observed#in#humans#involve#X#and#Y#chromosomes#because#any#monosomies#involving#autosomes#are#lethal.#The#other#trisomies#and#monosomies#are#usually#not#viable#in#humans.#!Q:#Know#that#changes#in#chromosome#structure#can#arise#due#to#abnormal#pairing#and#crossing#over#in#meiosis#or#to#errors#during#DNA#replication.#These#structural#changes#include#insertions,#duplications,#deletions,#and#translocations.###5Changes#in#chromosome#structure#can#occur#through#unequal#crossing#during#meiosis###Q:#Be#able#to#explain#the#role#of#polyploidy#in#the#formation#of#new#species.#### Polyploidy#originates#in#2#ways:##1) Addition#of#one#or#more#extra#sets#of#chromosomes5#identical#to#normal#haploid#complement#of#the#same#species#resulting#in#autopolyploidy##2) Or#the#combination#of#chromosome#sets#from#different#species#occurring#as#a#consequence#of#hybridization55formation#of#new#species##5Distinction#is#based#on#the#genetic#origin#of#the#extra#chromosome#sets###Q:#Understand#the#inheritance#of#Familial#Downs#Syndrome#and#understand#why#the#presence#of#a#translocation#can#result#in#increased#frequencies#of#miscarriages.###Familial!Downs!SyndromeQ!due#to#a#human#translocation;#most#downʼs#syndrome#is#due#to#trisomy#21#(due#to#nondisjunction),#but#this#is#an#inherited#translocation.#5#carrier#has#45#chromosomes#and#exhibits#the#normal#phenotypes#doesnʼt#contain#the#complete#diploid#amount#of#genetic#material.#Quantitative!Genetics/Polygenic!Inheritance!(Chapter!22)!!#Q:#Important#Terms/concepts#to#know:##Polygenic!inheritanceQ!also#known#as#quantitative#inheritance,#refers#to#inheritance#of#a#phenotypic#characteristic#(trait)#that#is#attributable#to#two#or#more#genes,#or#the#interaction#with#the#environment,#or#both.#Unlike#monogenic#traits,#polygenic#traits#do#not#follow#patterns#of#Medelʼs#inheritance#(separated#traits).#Instead,#their#phenotypes#typically#vary#along#a#continuous#gradient#depicted#by#a#bell#curve.##- Trait#is#determined#by#3+#gene#pairs#which#contribute#additively#to#the#phenotype#- each#pair#has#an#additive#and#a#non5additive#allele##- phenotype#reflects#the#total#number#of#additive#alleles#Discontinuous!TraitsQ!individuals#can#be#grouped#into#distinct#phenotypes##Continuous!traitsQ!individuals#display#a#continuous#range#of#phenotypes### ex:#height,#eye#color,#skin#color,#blood#pressure,#IQ,#behavioral#traits;#bell5shaped#distribution!!!##Multifactorial!traits5#polygenic#traits#that#are#influenced#by#the#environment.#Quantitative!traits5##Additive!and!nonadditive!alleles5#Complicated#of#simple##Twin!studies:!!Concordance5#When#a#pair#of#twins#display#the#same#phenotype##Monozygotic5#twins#should#be#100%#concordant##Dizygotic!twins5#less#than#100%#concordant##***You#should#understand#the#genetic#basis#for#traits#that#display#continuous#variation#(polygenic#inheritance#involving#additive#or#nonadditive#alleles)#and#have#a#general#understanding#of#the#types#of#traits#that#have#this#genetic#basis.###***You#should#be#able#to#do#simple#problems#that#require#determining#the#number#of#genes#that#control#a#polygenic#trait#and#the#amount#each#allele#contributes#to#the#phenotype,#similar#to#those#in#homework#3.####Q:#You#should#also#be#able#to#analyze#human#twin5study#data#and#identify#traits#that#are#determined#primarily#by#the#environment,#primarily#by#genes,#or#by#a#mixture#of#both#genes#and#environment.###- Many#polygenic#traits#are#also#influenced#by#the#environment#(multifactorial#traits)!!- Polygenic#traits#may#be#more#complicated#that#simple#additive#and#non5additive#alleles#!- When#a#pair#of#twins#display#the#same#phenotype55Concordant#!- If#the#trait#is#controlled#completely#by#genes,#monozygotic#twins#should#be#100%#concordant#and#Dizygotic#twins#should#be#<100%#concordant#!-
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