Chromosomal MutationsChromosomal Mutations

Changes in Chromosome Changes in Chromosome Number or StructureNumber or Structure

PRESENTED BY PRESENTED BY NAVEED UL MUSHTAQNAVEED UL MUSHTAQ

Chromosome MutationsChromosome Mutations

• A chromosome mutation is a change in A chromosome mutation is a change in the structure or arrangement of the the structure or arrangement of the chromosomeschromosomes

• Mutations are caused byMutations are caused by• Physical agents Physical agents e.g. X-rays and e.g. X-rays and

ultraviolet light ultraviolet light • Chemical mutagens Chemical mutagens such as nitrous acid such as nitrous acid

oror• By spontaneous By spontaneous way by unequal crossing way by unequal crossing

over.over.

Alterations in ChromosomeAlterations in ChromosomeStructural changesStructural changes•DELETIONDELETION•DUPLICATIONDUPLICATION•TRANSLOCATIONTRANSLOCATION•INVERSIONSINVERSIONSNUMERICAL CHANGESNUMERICAL CHANGES•AneuploidyExcess or Deficiency in a single chromosome•EUPLOIDY.Excess or Deficiency complete one or more sets of chromosomes

TYPES OF TYPES OF AneuploidyAneuploidy

• Monosomy (2n-1)Monosomy (2n-1)• NullisomyNullisomy• Trisomy(2n+1)Trisomy(2n+1)• Tetrasomy (2n+2)Tetrasomy (2n+2)

Human Chromosomal Human Chromosomal AneuploidsAneuploids

Down SyndromeDown Syndrome Trisomy 21Trisomy 21

Edward SyndromeEdward Syndrome Trisomy 18Trisomy 18

Patau SyndromePatau Syndrome Trisomy 13Trisomy 13

Autosomal AneuploidsAutosomal Aneuploids

Trisomy: three copies of one chromosomeTrisomy: three copies of one chromosome

AneuploidyAneuploidy• Arises by Non-disjunctionArises by Non-disjunction• Non-disjunction = failure of homologues Non-disjunction = failure of homologues

or chromatids to separate during meiosisor chromatids to separate during meiosis

Normal Normal MeiosisMeiosis

Non-disjunction Non-disjunction in Meiosis I in Meiosis I

Non-disjunction Non-disjunction in Meiosis II in Meiosis II

Incidence of Down Syndrome Increases with Maternal Age

1010 2020 3030 4040 505000

100100

200200

300300

400400

Age of Mother (years)Age of Mother (years)

Num

ber p

er 1

000

Birth

sNu

mbe

r per

100

0 Bi

rths

Human Chromosomal Human Chromosomal AneuploidsAneuploids

Sex Chromosome AneuploidsSex Chromosome Aneuploids

Turner SyndromeTurner Syndrome 45, XO45, XO

Triplo-XTriplo-X 47, XXX47, XXX

Klinefelter SyndromeKlinefelter Syndrome 47, XXY47, XXY

XYY SyndromeXYY Syndrome 47, XYY47, XYY

Sterile femaleSterile female

Fertile femaleFertile female

Sterile maleSterile male

Fertile maleFertile male

Applying KnowledgeApplying Knowledge

Lets determine how many Barr bodies would Lets determine how many Barr bodies would be found in each cell of someone withbe found in each cell of someone with::

Turner SyndromeTurner Syndrome 45, XO45, XO

Triplo-XTriplo-X 47, XXX47, XXX

Klinefelter SyndromeKlinefelter Syndrome 47, XXY47, XXY

XYY SyndromeXYY Syndrome 47, XYY47, XYY

00

22

11

00

EuploidyEuploidy

Excess or Deficiency in the Excess or Deficiency in the number of the number of the entire entire chromomosomal complementchromomosomal complement

• MonoploidMonoploid• DiploidDiploid• TriploidTriploid• TetraploidTetraploid

Chromosome Structure Chromosome Structure ChangesChanges

ChangeChange Description Description DeletionDeletion Loss of a chromosomal Loss of a chromosomal

segment segment can occur terminally or internally

DuplicationDuplication Repeat of a chromosomal Repeat of a chromosomal segment segment

TranslocatioTranslocationn

Movement of chromosomal Movement of chromosomal segment to non-homologous segment to non-homologous chromosome or genes from chromosome or genes from one linkage group transferred one linkage group transferred to anotherto another

InversionInversion Reversal of a chromosomal Reversal of a chromosomal segment segment (rotated 180(rotated 180oo))

Chromosome Chromosome DeletionDeletion

in Humans in Humans

Cri-du-chat Cri-du-chat syndromesyndrome

is correlated withis correlated witha deletion at the enda deletion at the endof chromosome 5of chromosome 5 Deleterious effects, Deleterious effects,

pseudosominance, pseudosominance, absence of crossing absence of crossing over etcover etc

Chromosome Chromosome Duplication Duplication in Humansin Humans

Small duplications Small duplications in chromosome 15 in chromosome 15 cause no cause no symptoms and no symptoms and no deleterious effectsdeleterious effects

Large duplication Large duplication (with inversion) (with inversion) causes mental causes mental retardationretardation

Chromosome Chromosome Translocation Translocation

in Humansin Humans

Reciprocal Reciprocal Translocation Translocation involves exchange involves exchange between two non-between two non-homologous homologous chromosomeschromosomes

Reciprocal Reciprocal translocation translocation between between chromosomes chromosomes 2 and 20 causes 2 and 20 causes Alagille SyndromeAlagille Syndrome

Effects heart, liver, Effects heart, liver, kidneys etckidneys etc

Chromosome Translocation in Chromosome Translocation in HumansHumans

Robertsonian Translocation involves a fusion of the Robertsonian Translocation involves a fusion of the long arms of two different chromosomeslong arms of two different chromosomes

Translocation Down Syndrome involves a Robertsonian Translocation Down Syndrome involves a Robertsonian Translocation between chromosomes 14 and 21 Translocation between chromosomes 14 and 21

Chromosome Chromosome Inversions Lead to Inversions Lead to

Unbalanced Meiotic Unbalanced Meiotic ProductsProducts

A paracentric inversion does not include the

centromere

A pericentric inversion includes

the centromere

SIGNIFICANCE OF SIGNIFICANCE OF INVERSIONINVERSION

• ORIGIN OF NEW SPECIESORIGIN OF NEW SPECIES• PROOF FOR THE OCCURANCE PROOF FOR THE OCCURANCE

OF CROSSING OVEROF CROSSING OVER• INVERSION IS CONSIDERED INVERSION IS CONSIDERED

AS CROSSING OVER AS CROSSING OVER REPRESSORSREPRESSORS

THANK THANK YOUYOU

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