Inheritance PrinciplesInheritance Principlesand and

Human GeneticsHuman Genetics

BioH - Chapter 11BioH - Chapter 11

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

ChromosomesChromosomes

Thomas Hunt MorganThomas Hunt Morgan– Studied fruit fliesStudied fruit flies– Found X and Y chromosomesFound X and Y chromosomes

KaryotypesKaryotypes

Karyotyping is a process that allows chromosomes to be presented in an orderly, easily compared manner

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

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

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)

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”

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%.

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

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

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

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)

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

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

Complex charactersComplex characters– Influenced both by Influenced both by environmentenvironment and and

genesgenes– Skin color, breast cancer, heightSkin color, breast cancer, height

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

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)

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

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

Chromosomal disordersChromosomal disordersChromosome problems, not genes

Duplication – a repeat of several gene sequences on the same chromosome

Deletion – loss of a chromosome segment

Inversion – gene sequence separated from chromosome, reinserted into same place, but in reverse

Translocation – transfer of one chromosome part to a non-homologous chromosome

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

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

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

XYY Condition – extra Y chromosome as result of non-disjunction

0.1% of males Taller than average Mild retardation

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

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

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

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