Inheritance Principles and Human Genetics BioH - Chapter 11.
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Transcript of Inheritance Principles and Human Genetics BioH - Chapter 11.
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Inheritance PrinciplesInheritance Principlesand and
Human GeneticsHuman Genetics
BioH - Chapter 11BioH - Chapter 11
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Genetics Vocabulary ReviewGenetics Vocabulary Review
Genes – units of information about heritable traits
Homologous chromosomes – similar chromosomes received from male and female that line up next to each during MetaphaseI in meiosis
Alleles – different forms of a gene
Locus – location on a chromosome where specific genes are found
Linkage – when genes on a chromosome “stay together” even during crossing-over
Genetic recombination – the “recombining” of genes as a result of crossing-over
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ChromosomesChromosomes
Thomas Hunt MorganThomas Hunt Morgan– Studied fruit fliesStudied fruit flies– Found X and Y chromosomesFound X and Y chromosomes
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KaryotypesKaryotypes
Karyotyping is a process that allows chromosomes to be presented in an orderly, easily compared manner
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Sex chromosomes (X, Y)Sex chromosomes (X, Y)– Contain genes that Contain genes that
determine the sex (gender) determine the sex (gender) of an individualof an individual
AutosomesAutosomes– Not directly involved in Not directly involved in
determining the sex of an determining the sex of an individualindividual
– Different organisms, Different organisms, different number different number
X Y
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Sex determinationSex determination– Sperm has equal chance of receiving X or YSperm has equal chance of receiving X or Y– Egg only receives XEgg only receives X
XX – femaleXX – female XY - maleXY - male
– Totally RANDOMTotally RANDOMprocessprocess
SSex-determination ex-determination RRegion egion YY (SRY) (SRY)– Found in mammalian Y chromosomeFound in mammalian Y chromosome– Gene codes protein to cause Gene codes protein to cause gonads to develop testesgonads to develop testes
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Gene locationGene location
Sex-linkedSex-linked– Traits coded for by an allele on a sex Traits coded for by an allele on a sex
chromosomechromosome– Could be on X or Y chromosomeCould be on X or Y chromosome– More X-linked genes because X is much More X-linked genes because X is much
largerlarger– If male carries a recessive allele on the If male carries a recessive allele on the
X chromosome, it will exhibit the traitX chromosome, it will exhibit the traitEx. Hemophilia (blood disorder)Ex. Hemophilia (blood disorder)
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Linked genesLinked genes
– Traits that are inherited togetherTraits that are inherited together– Makes a linkage groupMakes a linkage group– This happens because they are found This happens because they are found
close to each other in the same close to each other in the same chromosome and not as easily chromosome and not as easily genetically recombined by “crossing-genetically recombined by “crossing-over”over”
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Chromosome MapChromosome Map
A diagram that A diagram that shows the linear shows the linear order of genes on a order of genes on a chromosomechromosome
Map unit – Map unit – frequency of frequency of crossing over of 1%.crossing over of 1%.
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MutationsMutations Germ-cell mutationsGerm-cell mutations
– Occur in gametes Occur in gametes (may not be expressed until (may not be expressed until offspring)offspring)
Somatic-cell mutationsSomatic-cell mutations– Occur in body cellsOccur in body cells– May affect organsMay affect organs
Skin cancer and leukemiaSkin cancer and leukemia
– Lethal mutationsLethal mutationsCause death, often before birthCause death, often before birth
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Inheritance of TraitsInheritance of Traits PedigreesPedigrees
– A diagram showing how a trait is A diagram showing how a trait is inherited over several generationsinherited over several generations
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Russian Royal Family & Russian Royal Family & hemophiliahemophilia
Genetic abnormality – rare, uncommon trait versionGenetic disorder – inherited condition causing medical disordersSyndrome – recognized set of disorders that characterize a disorder
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Patterns of InheritancePatterns of Inheritance If a trait isIf a trait is
– AutosomalAutosomalAppears in both sexes equallyAppears in both sexes equallyDominantDominant
– Every individual with the trait will have parents Every individual with the trait will have parents with the traitwith the trait
BB or Bb (dominant trait will show)BB or Bb (dominant trait will show) bb (recessive trait will show)bb (recessive trait will show)
RecessiveRecessive– 1, 2, or no parent with the trait1, 2, or no parent with the trait– Bb X Bb will not show mutation but can produce Bb X Bb will not show mutation but can produce
children for the recessive allele (bb)children for the recessive allele (bb)– Bb (carrier) Bb (carrier)
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Genetic Trait and DisordersGenetic Trait and Disorders
Single-Allele traitsSingle-Allele traits– Controlled by a single allele of a geneControlled by a single allele of a gene– More 200 human traitsMore 200 human traits– Huntington’s diseaseHuntington’s disease
Forgetfulness and irritabilityForgetfulness and irritability
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Gene Inheritance & DisordersGene Inheritance & Disorders
Polygenic InheritancePolygenic Inheritance– Traits are influence by more than one Traits are influence by more than one
genegeneSkin color Skin color
– 3 to 6 genes3 to 6 genes– Genes control amount of melaninGenes control amount of melanin
Eye color, height, hair colorEye color, height, hair color
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Complex charactersComplex characters– Influenced both by Influenced both by environmentenvironment and and
genesgenes– Skin color, breast cancer, heightSkin color, breast cancer, height
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Multiple AllelesMultiple Alleles– Genes with 3 or more allelesGenes with 3 or more alleles– ABO blood groupsABO blood groups– IIAA, , IIBB, and , and II– IIA A andand I IBB are codominantare codominant
CodominanceCodominance– Both alleles are expressedBoth alleles are expressed– IIAAIIBB is type ABis type AB
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Incomplete dominanceIncomplete dominance– Trait that is displayed is intermediate Trait that is displayed is intermediate
between the two parents.between the two parents.– Hair typeHair type
Curly (CC) X Straight (cc)= Wavy hair (Cc)Curly (CC) X Straight (cc)= Wavy hair (Cc)
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X-linkedX-linked– Genes are linked to x-chromosomeGenes are linked to x-chromosome– ColorblindnessColorblindness
RecessiveRecessiveUnable to distinguish certain colors, eg. Unable to distinguish certain colors, eg.
green or redgreen or red
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Sex-influence traitsSex-influence traits– Males and females can show different Males and females can show different
phenotypes even with same genotypesphenotypes even with same genotypes– AutosomalAutosomal– Type of BaldnessType of Baldness
Dominant in malesDominant in malesRecessive in femalesRecessive in females
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Chromosomal disordersChromosomal disordersChromosome problems, not genes
Duplication – a repeat of several gene sequences on the same chromosome
Deletion – loss of a chromosome segment
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Inversion – gene sequence separated from chromosome, reinserted into same place, but in reverse
Translocation – transfer of one chromosome part to a non-homologous chromosome
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Chromosome number disordersChromosome number disordersNondisjunction – one or more pairs of chromosomes fail to separate during mitosis or meiosis (produces condition known as aneuploidy – more or less chromosomes than the parental number)
Down Syndrome – one extra chromosome at #21
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Sex Chromosome number Sex Chromosome number changeschanges
Turner syndrome – inheriting only one X chromosome with no additional X or Y chromosomeMost X0 zygotes spontaneously abort 0.01–0.04% of femalesNon-functional ovaries(infertile)Short heightNormal intelligence
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Kleinfelter Syndrome – one extra X chromosome with normal XY (XXY)
0.05-0.2% of males Conditions develop after
puberty Smaller testes - usually
sterile (not always) Taller than normal Normal intelligence Very subtle phenotype
characteristics
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XYY Condition – extra Y chromosome as result of non-disjunction
0.1% of males Taller than average Mild retardation
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DetectionDetection
AmnioncentesisAmnioncentesis– Removal of amniotic Removal of amniotic
fluid from the fluid from the amnion, the sac amnion, the sac surrounding the surrounding the fetusfetus
– Between 14 – 16 Between 14 – 16 week of pregnancyweek of pregnancy
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Chorionic villi Chorionic villi samplingsampling– Cells derived from Cells derived from
the zygote that the zygote that grow between grow between uterus and placentauterus and placenta
– Between 8Between 8thth and and 1010thth week week
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Genetic counselingGenetic counseling– Informing a person or couple about their Informing a person or couple about their
genetic makeupgenetic makeup– Form of medical guidance about Form of medical guidance about
problems that might affect their problems that might affect their offspringoffspring
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TreatmentTreatment
Usually treat symptomsUsually treat symptoms Gene therapyGene therapy
– Replacement of defective genes with a Replacement of defective genes with a healthy onehealthy one
– Somatic cell gene therapy (body cells)Somatic cell gene therapy (body cells)– Germ cell gene therapy (eggs or Germ cell gene therapy (eggs or
sperms)sperms)Poses risks and ethical issuesPoses risks and ethical issues