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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?