Sex Linked Traits Sex chromsomes: 1 pair female = XXmale = XY X chromosome: Y chromosome: larger,...
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Transcript of Sex Linked Traits Sex chromsomes: 1 pair female = XXmale = XY X chromosome: Y chromosome: larger,...
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Sex Linked Traits
Sex chromsomes: 1 pair
female = XX male = XY
X chromosome: Y chromosome:larger, more genes male traitsfemale traits distribution of body fatColor vision height genesBlood-clotting hair on earsHair on head
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Genotypes Phenotypes
XN XN
XN Xn
Xn Xn
XN Y
Xn Y
Color Blindness: X- linked
normal
carrier
colorblind
normal
colorblind
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Are You Color Blind?
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Hemophilia: X- linked
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X- linked Traits
• Males need only 1 bad allele, females need 2 bad alleles to be expressed
• Males have a greater chance of expressing X-linked traits
Xn Y
XN YXN Xn
Xn YXN Xn
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Sex-Chromosomes Switched:
some organisms have female = XY male = XX
birds, moths, butterflies, some reptiles, some fish
Some may use different letters besides X and YChickens: female = WZ male = WW
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Other sex-linked disordersOther sex-linked disorders
• Duchenne’s muscular dystrophyDuchenne’s muscular dystrophy
• Some forms of baldnessSome forms of baldness
• Retinitis pigmentosaRetinitis pigmentosa
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Predict the phenotype (sex) Predict the phenotype (sex) of the following genotypes:of the following genotypes:
• XXXX
• XYXY
• XXXXXX
• XYYXYY
• XXYXXY
• XOXO
• YOYO
(O = no other sex chrm present)(O = no other sex chrm present)
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The X chrm encodes The X chrm encodes proteins we all needproteins we all need
• In females, one of the two X’s is randomly In females, one of the two X’s is randomly inactivated in all somatic cellsinactivated in all somatic cells
• Females are genetic Females are genetic mosaicsmosaics for X-linked for X-linked genesgenes
• Barr body = inactive X chromosomeBarr body = inactive X chromosome
• ––>> Dosage Compensation Dosage Compensation
Do women have more of those proteins?
Why?-because too much of that good stuff would be bad
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Calico CatCalico Cat
Is there a human calico cat?
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X-linked conditions that show a X-linked conditions that show a partial phenotype in femalespartial phenotype in females
• Calico catCalico cat– Hemizygous males: brown or orange or whiteHemizygous males: brown or orange or white– Het females: alternating patches of colorHet females: alternating patches of color
• Absence of sweat glands Absence of sweat glands – hemizygous males : with few sweat glandshemizygous males : with few sweat glands– het females : alternating patcheshet females : alternating patches
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Human somatic cells are Human somatic cells are diploid:diploid:• 46 chromosomes46 chromosomes
– 22 pairs of autosomes (1, 2, … 22)22 pairs of autosomes (1, 2, … 22)– 1 pair of sex chromosomes (XX or XY).1 pair of sex chromosomes (XX or XY).
Human gametes are haploid:Human gametes are haploid: • 23 chromosomes 23 chromosomes
– 1 each of the 22 autosomes1 each of the 22 autosomes– X or YX or Y
• = “haploid set” or “monoploid set”= “haploid set” or “monoploid set”
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Euploid, aneuploidEuploid, aneuploid
• A cell that contains a multiple of the A cell that contains a multiple of the haploid set of chromosomes is called haploid set of chromosomes is called euploideuploid..
• Cells that do not contain a multiple of Cells that do not contain a multiple of the haploid set are called the haploid set are called aneuploidaneuploid..
• Aneuploid cells contain missing or Aneuploid cells contain missing or additional chromosomesadditional chromosomes
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Common types of Common types of aneuploidyaneuploidy
• Monosomy - only 1 copy of a given Monosomy - only 1 copy of a given chrm in an otherwise diploid cell.chrm in an otherwise diploid cell.
• Trisomy - 3 copiesTrisomy - 3 copies
The most frequent cause of The most frequent cause of aneuploidyaneuploidy
… … is chromosomal is chromosomal nondisjunctionnondisjunction..
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Meiosis Error: Meiosis Error: NondisjunctionNondisjunction
• Chrms or chromatids fail to Chrms or chromatids fail to “disjoin” during meiosis“disjoin” during meiosis
• Fertilization produces a zygote Fertilization produces a zygote with monsomy or trisomy.with monsomy or trisomy.
• Risk of nondisjunction increases Risk of nondisjunction increases dramatically with maternal age.dramatically with maternal age.
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PolyploidyPolyploidy• Has entire extra sets of chromosomes (3n, 4n, Has entire extra sets of chromosomes (3n, 4n,
etc.)etc.)
• 35% of flowering plants are polyploid, as well 35% of flowering plants are polyploid, as well as several of agricultural value.as several of agricultural value.
• Triploid plants often infertile Triploid plants often infertile – pairing and segregation is disrupted in meiosispairing and segregation is disrupted in meiosis– commercially beneficial (e.g. seedless fruit)commercially beneficial (e.g. seedless fruit)
• In humans, polyploidy is lethal before or In humans, polyploidy is lethal before or shortly after birthshortly after birth
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Sex Chromosome Sex Chromosome AneuploidiesAneuploidies• trisomy-X = 47, XXX (female) trisomy-X = 47, XXX (female)
– 0.1% female births0.1% female births
• double-Y = 47, XYY (male) double-Y = 47, XYY (male) 0.1% male 0.1% male birthsbirths
• Klinefelter Syndrome = 47, XXY (male, sterile) Klinefelter Syndrome = 47, XXY (male, sterile) 0.1% male births0.1% male births
• Turner Syndrome = 45, X Turner Syndrome = 45, X (female, sterile) (female, sterile) 0.5% female births0.5% female births
• (45, Y = embryonic lethal)(45, Y = embryonic lethal)
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Klinefelter Syndrome = 47, XXY (male, sterile) 0.1% male births
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Turner Syndrome = 45, X (female, sterile,do not developSecondary sex characteristics)0.5% female births
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•Trisomy of chromosome 21 = most Trisomy of chromosome 21 = most common autosomal (non-sex chrm) common autosomal (non-sex chrm) aneuploidy (1/800 live births).aneuploidy (1/800 live births).
•Approx. 75% of trisomy 21 Approx. 75% of trisomy 21 conceptions are spontaneously conceptions are spontaneously aborted (miscarriages).aborted (miscarriages).
• Down Syndrome = genetic disorder Down Syndrome = genetic disorder due to trisomy 21.due to trisomy 21.
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Down syndromeDown syndrome• Mental retardationMental retardation
• Gastrointestinal tract Gastrointestinal tract obstructionobstruction
• Congenital heart defectsCongenital heart defects
• Respiratory infectionsRespiratory infections
• 15-20 X higher risk of 15-20 X higher risk of leukemialeukemia
• Characteristic appearanceCharacteristic appearance
• Research - determine the Research - determine the critical genes on chrm 21 critical genes on chrm 21 responsibleresponsible
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Other AneuploidiesOther Aneuploidies• Trisomy 13 - Edward SyndromeTrisomy 13 - Edward Syndrome
(1/10,000 live births)(1/10,000 live births)
• Trisomy 18 - Patau SyndromeTrisomy 18 - Patau Syndrome(1/6,000 live births)(1/6,000 live births)
• 95% affected fetuses spontaneously 95% affected fetuses spontaneously aborted.aborted.
• 90% mortality during first year of life.90% mortality during first year of life.
• All other trisomies and monosomies are All other trisomies and monosomies are embyronic lethals, resulting in embyronic lethals, resulting in spontaneously aborted fetuses.spontaneously aborted fetuses.
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Chromosome Chromosome RearrangemeRearrangementsnts
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Chrm Abnormalities and Chrm Abnormalities and Pregnancy LossPregnancy Loss
• About 1/3 of human pregnancies are lost About 1/3 of human pregnancies are lost spontaneously after implantationspontaneously after implantation
• Chrm abnormalities are the leading known Chrm abnormalities are the leading known cause of pregnancy losscause of pregnancy loss
• A minimum 10-15% of conceptions have a A minimum 10-15% of conceptions have a chrm abnormalitychrm abnormality
• At least 95% of these conceptions At least 95% of these conceptions spontaneously abortspontaneously abort
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Birth DefectsBirth Defects
• Most common cause of infant death in U.S.Most common cause of infant death in U.S.
• 2-3% of babies are born with a recognizable 2-3% of babies are born with a recognizable birth defectbirth defect
• Can be caused by genetic defectsCan be caused by genetic defects– Chrm abnormalityChrm abnormality– Mutation in gene involved in developmentMutation in gene involved in development
• Can be caused by environmentCan be caused by environment– Fetal alcohol syndrome Fetal alcohol syndrome - Rubella- Rubella– ThalidomideThalidomide - Low folic acid- Low folic acid
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Chrm RearrangementsChrm Rearrangements
•ReciprocReciprocationation TranslocTranslocalal
•InInrevrevsionsion
•DeltionDeltion
•DuplicDuplicliclicationation
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Chrm Rearrangement:Chrm Rearrangement:TranslocationTranslocation
• Interchange of genetic info Interchange of genetic info between non-homologous between non-homologous chrmschrms
• Present in at least 1/500 Present in at least 1/500 peoplepeople
• Probably result from a mistake Probably result from a mistake by the recombination by the recombination machinerymachinery
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Reciprocal Translocation between p arms of 1 and 9
telomere
telomere
centromere
Chrm 1
Chrm 9
{q arm
{p arm
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This pairing in meiosis I
Chrm 1
Chrm 9
Metaphase plate
Leads to...
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These gametes:
NormalCarrier
NormalAneuploid Aneuploid
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Chrm Chrm Rearrangement:Rearrangement: InversionInversiongenetic rearrangement in which the genetic rearrangement in which the
order of genes is reversed in a order of genes is reversed in a chromosome segment chromosome segment
ABC
DEFGH
ABC
DGFEH
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ChromosomeChromosome InversionsInversions
• As with translocations, genetic As with translocations, genetic information unchanged (except information unchanged (except at/near breakpoints)at/near breakpoints)
• At synapsis (= homologous At synapsis (= homologous pairing), inversion loops formpairing), inversion loops form
• If a crossover (recombination) If a crossover (recombination) occurs in the loop, then two occurs in the loop, then two abnormal chrms resultabnormal chrms result
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Chromosome DeletionsChromosome Deletions• Deletions = missing chrm segmentDeletions = missing chrm segment
• Large deletions often lethal (even in heterozygote)Large deletions often lethal (even in heterozygote)
ABC
DEFGH
ABC
DGH
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Some Deletion Some Deletion SyndromesSyndromes• Cri-du-chat (del 5p)Cri-du-chat (del 5p)• Wolf-Hirschhorn (del 4p)Wolf-Hirschhorn (del 4p)• Prader-Willi/Angelmann (del 15q11-13)Prader-Willi/Angelmann (del 15q11-13)• Langer-Giedion (del 8q24)Langer-Giedion (del 8q24)• Miller-Dieker (del 17p13.3)Miller-Dieker (del 17p13.3)• DiGeorge Anamoly (del 22q11)DiGeorge Anamoly (del 22q11)• Smith-Magenis (del 17p11.2)Smith-Magenis (del 17p11.2)• Williams (del 7q1)Williams (del 7q1)• Wilms Tumor/Aniridia (del 11p13)Wilms Tumor/Aniridia (del 11p13)
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Gene DuplicationsGene Duplications
• Chromosome segment present Chromosome segment present
in multiple copiesin multiple copies
• Provide material for evolutionProvide material for evolution
• Tandem duplications Tandem duplications – repeatedrepeated segments are adjacent segments are adjacent – often result from unequal crossing-overoften result from unequal crossing-over
ABC
DEF
ABC
DEEF
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Genomic ImprintingGenomic Imprinting