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Chromosome AnalysisChromosome Analysis
National DNA DayNational DNA Day
April 25, 2005April 25, 2005
Image retrieved from virtualsciencefair.org on 2/26/08
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What are chromosomes?What are chromosomes?
Chromosomes are structures found in theChromosomes are structures found in the
nucleus of cellsnucleus of cells Chromosomes carry all of our genes, andChromosomes carry all of our genes, and
therefore all of our genetic informationtherefore all of our genetic information Humans have 46 chromosomes, or 23Humans have 46 chromosomes, or 23
pairs, to carry our approximately 25,000pairs, to carry our approximately 25,000
genesgenes
The first 22 pairs are calledThe first 22 pairs are called autosomesautosomes
The 23The 23rdrd pair are the sex chromosomes orpair are the sex chromosomes orgonosomesgonosomesthis pair will either be XX or XYthis pair will either be XX or XY
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The KaryotypeThe Karyotype
A karyotype is a pattern or picture of chromosomesA karyotype is a pattern or picture of chromosomes
The chromosomes are paired and arranged accordingThe chromosomes are paired and arranged accordingto sizeto size Each chromosome is paired with itsEach chromosome is paired with its homologoushomologous chromosomechromosome
its exact match in size and structure, though the homologousits exact match in size and structure, though the homologous
chromosomes may carry different alleles of the same genechromosomes may carry different alleles of the same gene Then the chromosome pairs are labeledThen the chromosome pairs are labeled
The autosomes are numbered 1 through 22 according to sizeThe autosomes are numbered 1 through 22 according to size
The sex chromosomes are a different storyThe sex chromosomes are a different story The X and X or the X and Y are paired, then placed at the end,The X and X or the X and Y are paired, then placed at the end,
even though they are not necessarily the smallesteven though they are not necessarily the smallestchromosomeschromosomes
These chromosomes do not receive a numberThese chromosomes do not receive a numberjust XX or XYjust XX or XY
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Using a KaryotypeUsing a Karyotype
A karyotype allows aA karyotype allows a cytogeneticistcytogeneticist or labor lab
technician to examine the chromosomestechnician to examine the chromosomesand see if there is anything extra orand see if there is anything extra or
missing, or if the structure of themissing, or if the structure of the
chromosomes is different than usualchromosomes is different than usual
Sometimes there is an obviousSometimes there is an obvious
abnormality, but other times it takes veryabnormality, but other times it takes verycareful observation to spot somethingcareful observation to spot something
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Karyotype Example
This is an example of a completed karyotype Since both an X and a Y chromosome are present, this is a karyotype of a
male
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Creating a KaryotypeCreating a Karyotype
Open your envelopes and empty the contents onOpen your envelopes and empty the contents on
your deskyour desk Arrange the chromosomes to create a karyotypeArrange the chromosomes to create a karyotype
Chromosomes should all be paired together andChromosomes should all be paired together and
arranged from largest to smallestarranged from largest to smallest The sex chromosomes should go last, after the otherThe sex chromosomes should go last, after the other
22 pairs22 pairs
Go ahead and number your chromosome pairs onceGo ahead and number your chromosome pairs oncethey are paired and arrangedthey are paired and arranged
Be carefulBe carefulyour karyotype might contain anyour karyotype might contain an
abnormality!abnormality!
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What kind of results do youWhat kind of results do you
see?see?
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Trisomy 21Trisomy 21
Trisomy 21 is theTrisomy 21 is the
presence of 3presence of 3chromosome 21chromosome 21s.s.Trisomy 21 causes theTrisomy 21 causes thecondition commonlycondition commonly
known as Downknown as Downsyndromesyndrome
The extra chromosomeThe extra chromosomeleads to the specificleads to the specific
characteristics of Downcharacteristics of Downsyndrome, some of whichsyndrome, some of whichare very familiarare very familiar However, not all individualsHowever, not all individuals
with Down syndrome willwith Down syndrome willshow the exact sameshow the exact samecharacteristicscharacteristicsthere is athere is agreat deal of variabilitygreat deal of variability
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Trisomy 21/Down syndromeTrisomy 21/Down syndrome
Individuals with Down syndrome have a typical facialIndividuals with Down syndrome have a typical facialappearanceappearance
All have some degree of mental retardation, but for mostAll have some degree of mental retardation, but for mostit is mild or moderateit is mild or moderate Can learn to read, write, do some math, and live dayCan learn to read, write, do some math, and live day--toto--day withday with
minimal assistance from othersminimal assistance from others Others require a lot of attention and careOthers require a lot of attention and care
There are several possible health concerns, includingThere are several possible health concerns, including
heart problems, hearing loss, feeding concerns, andheart problems, hearing loss, feeding concerns, andothersothers Individuals with Down syndrome are now living longer than inIndividuals with Down syndrome are now living longer than in
the pastthe pastinto their 50into their 50s and 60s and 60ss
We are now discovering that those individuals who survive toWe are now discovering that those individuals who survive tothis age are at very high risk of developing Alzheimerthis age are at very high risk of developing Alzheimers diseases disease
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Trisomy 13Trisomy 13 Trisomy 13 is the presence of 3Trisomy 13 is the presence of 3
chromosome 13chromosome 13s. Trisomy 13s. Trisomy 13causes the condition sometimescauses the condition sometimesknown asknown as PatauPatau syndromesyndrome
Trisomy 13 is a very seriousTrisomy 13 is a very seriousconditionconditiononly about 5% ofonly about 5% ofbabies with the disorder survivebabies with the disorder survivepast their first yearpast their first year
Most pregnancies involvingMost pregnancies involvingTrisomy 13 end in miscarriageTrisomy 13 end in miscarriage
Children with Trisomy 13 usuallyChildren with Trisomy 13 usuallyhave a lot of trouble breathing,have a lot of trouble breathing,especially when they sleep, andespecially when they sleep, and
many have seizures. Allmany have seizures. Allindividuals with Trisomy 13 haveindividuals with Trisomy 13 havesevere mental retardationsevere mental retardation
There are other characteristicsThere are other characteristicscommonly seen in people withcommonly seen in people withTrisomy 13, including a smallTrisomy 13, including a smallhead, extra fingers and/or toes,head, extra fingers and/or toes,and a cleft lip or cleft palateand a cleft lip or cleft palate
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Trisomy 18Trisomy 18
Trisomy 18 is the presence of 3Trisomy 18 is the presence of 3chromosome 18chromosome 18s. Trisomy 18s. Trisomy 18causes the condition sometimescauses the condition sometimes
known as Edwards syndromeknown as Edwards syndrome Trisomy 18 is another very seriousTrisomy 18 is another very serious
conditionconditiononly about 10% of babiesonly about 10% of babieswith the disorder survive past theirwith the disorder survive past theirfirst year. A majority of babies whofirst year. A majority of babies who
survive are female.survive are female. Most pregnancies involving TrisomyMost pregnancies involving Trisomy
18 end in miscarriage18 end in miscarriage
Children with Trisomy 18 usuallyChildren with Trisomy 18 usuallyhave breathing problems, difficultyhave breathing problems, difficulty
eating, and many have seizures.eating, and many have seizures.Some have serious heart conditions.Some have serious heart conditions.All individuals with Trisomy 18 haveAll individuals with Trisomy 18 havesevere mental retardation.severe mental retardation.
Most babies with Trisomy 18 areMost babies with Trisomy 18 arevery small and have certainvery small and have certainrecognizable facial features. Theyrecognizable facial features. Theyalso tend to overlap their fingers in aalso tend to overlap their fingers in avery distinct patternvery distinct pattern
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47, XXY47, XXY
An individual with theAn individual with thegenotype 47, XXY is malegenotype 47, XXY is male
The person has 47The person has 47chromosomes just likechromosomes just likesomeone with Trisomy 21,someone with Trisomy 21,13, or 18, but does not have13, or 18, but does not havea typicala typical trisomy,trisomy, as he hasas he has
two of one chromosome andtwo of one chromosome andone of anotherone of another
One could say, though, thatOne could say, though, thatsuch an individual has a sexsuch an individual has a sexchromosome trisomychromosome trisomy
The extra X chromosomeThe extra X chromosomeleads to features of theleads to features of thecondition commonly knowncondition commonly known
as Klinefelter syndromeas Klinefelter syndrome
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Klinefelter syndromeKlinefelter syndrome
Affects about 1 in 1000 malesAffects about 1 in 1000 males
Most males are taller than average and may have aMost males are taller than average and may have adifferent distribution of body fat (e.g. more than usual indifferent distribution of body fat (e.g. more than usual inthe hips or chest)the hips or chest) Also tend to have sparse facial and body hairAlso tend to have sparse facial and body hair
Some have a degree of mental retardation, but manySome have a degree of mental retardation, but manyhave normal intelligencehave normal intelligence
The most common feature of Klinefelter syndrome isThe most common feature of Klinefelter syndrome is
infertilityinfertility It is estimated about 2% of infertile men haveIt is estimated about 2% of infertile men have KlinefelterKlinefeltersssyndromesyndrome
Since the characteristics of the syndrome are not alwaysSince the characteristics of the syndrome are not always
obvious, many males with Klinefelter will never beobvious, many males with Klinefelter will never bediagnoseddiagnosed
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45, X45, X An individual with theAn individual with the
genotype 45, X isgenotype 45, X isphenotypicallyphenotypically femalefemale
The person has 45The person has 45chromosomes instead ofchromosomes instead ofthe usual 46the usual 46
Instead of a trisomy, thisInstead of a trisomy, thiswould be called awould be called amonosomymonosomy
One copy of an XOne copy of an Xchromosome =chromosome = monosomymonosomyXX
MonosomyMonosomy X is the onlyX is the onlymonosomymonosomy known to beknown to becompatible with lifecompatible with life
Having only one copy of anHaving only one copy of anX chromosome leads to theX chromosome leads to thefeatures of the conditionfeatures of the conditionknown as Turner syndromeknown as Turner syndrome
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Turner syndromeTurner syndrome
Affects about 1 in 5000 newborn femalesAffects about 1 in 5000 newborn females
Females with Turner syndrome are shorter thanFemales with Turner syndrome are shorter thanaverage and have other noticeable physicalaverage and have other noticeable physicalfeaturesfeatures
Swelling of the hands and feet, webbing of the neck,Swelling of the hands and feet, webbing of the neck,broad chestbroad chest
May also have features which affect their health,May also have features which affect their health,including heart disease and aincluding heart disease and a horseshoehorseshoe--shapedshaped
kidneykidney
Individuals with Turner syndrome will notIndividuals with Turner syndrome will nottypically have mental retardation, but may havetypically have mental retardation, but may have
specific learning disabilitiesspecific learning disabilities
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Questions for DiscussionQuestions for Discussion
Why would the presence (or absence) of aWhy would the presence (or absence) of achromosome lead to certain characteristics in achromosome lead to certain characteristics in aperson?person?
Why wouldnWhy wouldnt the physical, mental, andt the physical, mental, andbehavioral features be exactly the same for twobehavioral features be exactly the same for two
people with the same extra (or missing)people with the same extra (or missing)chromosome?chromosome?
Why are babies with trisomy 21 more likely toWhy are babies with trisomy 21 more likely to
survive than babies with trisomy 13 or 18?survive than babies with trisomy 13 or 18? Why do you thinkWhy do you think monosomymonosomy X (TurnerX (Turner
syndrome) is the onlysyndrome) is the only monosomymonosomy in which thein which theindividual survives?individual survives?