Human Genetics

Human GeneticsHuman Genetics

• Genetic abnormalityGenetic abnormality = a genetic = a genetic condition that is a deviation from condition that is a deviation from the average: the average: notnot life-threatening life-threatening

• Genetic disorderGenetic disorder = describes = describes conditions that conditions that cause medical cause medical problemsproblems

Human Genetic DisordersHuman Genetic Disorders

KaryotypeKaryotype• A A pictorial displaypictorial display of of metaphase metaphase

chromosomeschromosomes from a mitotic cell from a mitotic cell • Chromosomes are identified and arranged Chromosomes are identified and arranged

by their by their characteristic characteristic size, shape, size, shape, centromere centromere location and location and staining patternsstaining patterns

Human KaryotypeHuman Karyotype

Detects some Detects some fetal fetal abnormalities abnormalities through through karyotypingkaryotyping

Amnio-Amnio-centesiscentesis

Human Chromosome Human Chromosome CharacteristicsCharacteristics

• Diploid set for Diploid set for humans humans = = 4646

• AutosomesAutosomes = = 2222

• Female-sex chromosomes = Female-sex chromosomes = homologous homologous (XX)(XX)

• Male-sex chromosomes = Male-sex chromosomes = non-homologous non-homologous (XY)(XY)

• Either parent can Either parent can carry the carry the recessive allele on recessive allele on an autosome.an autosome.– HeterozygotesHeterozygotes

are symptom-are symptom-free.free.– HomozygotesHomozygotes

are are affectedaffected..

Autosomal RecessiveAutosomal Recessive

• One defective or absent One defective or absent gene can result in the gene can result in the inability to make a inability to make a specific enzymespecific enzyme

• Recombinant DNA Recombinant DNA techniquestechniques may someday may someday correct faulty correct faulty chromosomeschromosomes

Genetic Errors of MetabolismGenetic Errors of Metabolism

Obesity gene discovered

• GalactosemiaGalactosemia– Inability to metabolize lactoseInability to metabolize lactose

• Cystic FibrosisCystic Fibrosis– Inability to Inability to

breakdown breakdown mucous in lungs mucous in lungs and other organs and other organs

Genetic Errors of MetabolismGenetic Errors of Metabolism

• Missing an enzyme Missing an enzyme to break down lipids, to break down lipids, leading to destruction leading to destruction of central nervous sys. of central nervous sys.

• Mainly found in Mainly found in Eastern European Eastern European JewishJewish decendents decendents 1:27 is a carrier1:27 is a carrier– Judaism is trying to eliminate gene Judaism is trying to eliminate gene

through non-breeding between through non-breeding between couples couples who are carrierswho are carriers

Tay-Sachs DiseaseTay-Sachs Disease

• RecessiveRecessive, changes the shape of , changes the shape of the hemoglobin moleculethe hemoglobin molecule– ExtremelyExtremely painful, debilitating painful, debilitating

– Only distorts when Only distorts when deoxygenateddeoxygenated

Sickle-cell AnemiaSickle-cell Anemia

• High frequency in High frequency in black populationsblack populations

• SS= no sickle-cellSS= no sickle-cell

• Ss = mild symptomSs = mild symptom

• ssss = full blown disease = full blown disease

Sickle-cell AnemiaSickle-cell Anemia

Heterozygote SuperiorityHeterozygote Superiority• HeterozygotesHeterozygotes receive protection from receive protection from

symptoms of sickle-cell AND malaria - symptoms of sickle-cell AND malaria - advantage in malarial countriesadvantage in malarial countries

• SS + malaria = SS + malaria = malariamalaria only only

• Ss + malaria = Ss + malaria = no symptoms of eitherno symptoms of either

• ss + malaria = ss + malaria = mildmild sickle cell sickle cell

• Sickle cells become trapped and destroyed Sickle cells become trapped and destroyed in the spleen causing in the spleen causing SplenicSplenic SequestionSequestion

• AnemiaAnemia

• Pain episodesPain episodes

• Stroke or Brain DamageStroke or Brain Damage

• Kidney failureKidney failure

• PneumoniaPneumonia

• Increased InfectionsIncreased Infections

ComplicationsComplications

• Lack one enzyme to break Lack one enzyme to break down down phenylalaninephenylalanine– Products Products

accumulate, cause accumulate, cause mental retardation, mental retardation, other severe other severe symptomssymptoms– Treated through Treated through

dietary restrictionsdietary restrictions

PKUPKU

• A dominant allele is A dominant allele is always always expressedexpressed and if it reduces the and if it reduces the chance of surviving or chance of surviving or reproducing, its frequency reproducing, its frequency should should decreasedecrease

• MutationsMutations and conditions that set and conditions that set in in late in lifelate in life work against this work against this

Autosomal DominantAutosomal Dominant

• AchondroplasiaAchondroplasia ( (DwarfismDwarfism))–Lacks functional gene for somatropic Lacks functional gene for somatropic

hormone in the pituitaryhormone in the pituitary

Autosomal Autosomal DominantDominant

• Acromegaly (Acromegaly (Gigantism)Gigantism)– Pituitary produces Pituitary produces

excess growth excess growth hormoneshormones

Errors in MetabolismErrors in Metabolism

• A serious degeneration of the A serious degeneration of the nervous system with an onset from nervous system with an onset from age 40 onwardage 40 onward - Fatal, - Fatal, no cureno cure

• Gene has Gene has been been found found

Huntington’s DisorderHuntington’s Disorder

Woody Guthrie

Would Would you want you want to know?to know?

WHY???WHY???

• Mutated gene Mutated gene occurs only on occurs only on the the XX chromosomechromosome

X-Linked RecessiveX-Linked Recessive

• Heterozygous females are Heterozygous females are phenotypically normalphenotypically normal

• MalesMales are affected because are affected because they have only one they have only one allele for the trait (on the allele for the trait (on the X chromosome) and it X chromosome) and it can be recessive. can be recessive.

X-Linked RecessiveX-Linked Recessive

• Color-blindnessColor-blindness

• BaldnessBaldness

X-Linked RecessiveX-Linked Recessive

• Inability of blood to Inability of blood to clotclot because genes because genes do not code for clotting agent(s)do not code for clotting agent(s)

Hemophilia AHemophilia A

Queen Victoria: a CarrierQueen Victoria: a Carrier

• Afflicted persons need frequent Afflicted persons need frequent transfusionstransfusions and infusions of and infusions of artificial artificial clotting agentsclotting agents

• Internal bleedingInternal bleeding from falls or bruising from falls or bruising the most seriousthe most serious

• Cummulative scarring may Cummulative scarring may restrict movementrestrict movement

Hemophilia AHemophilia A

• Similar to X-linked recessive alleles, Similar to X-linked recessive alleles, except the allele is also expressed in except the allele is also expressed in heterozygous femalesheterozygous females

• Examples: faulty Examples: faulty enamel (of the teeth) traitenamel (of the teeth) trait

X-Linked DominanceX-Linked Dominance

• AneuploidyAneuploidy = one extra or one less = one extra or one less chromosome, may affect one of every chromosome, may affect one of every two newly fertilized eggstwo newly fertilized eggs

• PolyploidyPolyploidy = three or more of each = three or more of each chromosome, is common in plants but chromosome, is common in plants but is lethal to the zygote if it occurs in is lethal to the zygote if it occurs in humanshumans

Patterns of InheritancePatterns of Inheritance

Meiotic ErrorsMeiotic Errors• NondisjunctionNondisjunction- - homologues don't homologues don't

separate in meiosis 1separate in meiosis 1

• Homologues Homologues don't separate don't separate in meiosis 1in meiosis 1

Non-Non-disjunction disjunction

in Sex in Sex ChromosomesChromosomes

Trisomy 21/Down SyndromeTrisomy 21/Down Syndrome

• Occurs more frequently Occurs more frequently in children born to in children born to older women older women andand men men

– 1 in 801 in 80 births after 40 yrs births after 40 yrs

– 1in 401in 40 births after 45 yrs births after 45 yrs

• Most children show mental deficienciesMost children show mental deficiencies– Many lead productive livesMany lead productive lives

– 40% have heart defects40% have heart defects

– many have diabetes and many have diabetes and

have weight issueshave weight issues

Down SyndromeDown Syndrome

• XOXO– Females with only one X chromosome, Females with only one X chromosome,

mostly due to nondisjunction in mostly due to nondisjunction in fatherfather– Most are spontaneously abortedMost are spontaneously aborted– Sterile, short stature, Sterile, short stature,

heart defects, premature heart defects, premature aging, shorter livesaging, shorter lives

• YOYO = = LETHALLETHAL

Turner SyndromeTurner Syndrome

• XXY XXY conditioncondition– Most from non-disjunction in mother Most from non-disjunction in mother

– Tall, some mental slownessTall, some mental slowness

– Poor male sex organ development; Poor male sex organ development; breast development; breast development;

usually sterileusually sterile

Klinefelter SyndromeKlinefelter Syndrome

• XYYXYY condition condition• Fertile, tall, slight retardation, Fertile, tall, slight retardation,

increased strength & aggressionincreased strength & aggression • NOT predisposed to crime - a fallacyNOT predisposed to crime - a fallacy

Jacob SyndromeJacob Syndrome

• TranslocationTranslocation– TransferTransfer of of

a a piece of piece of one one

chromosome chromosome

to anotherto another

Changes in Changes in Chromosome StructureChromosome Structure

• DeletionsDeletions– Loss of a Loss of a

chromosome region chromosome region by by viral attack, viral attack, chemicals, chemicals, irradiation, or irradiation, or other other environmental environmental factorsfactors

Changes in Changes in Chromosome StructureChromosome Structure

• DeletionDeletion or or translocationtranslocation of of material from 5th chromosomematerial from 5th chromosome–““Cry of the Cat”Cry of the Cat” (French) - sound (French) - sound

many children make many children make when cryingwhen crying

– Severe mental Severe mental retardation; internal retardation; internal problemsproblems

Cri-du-ChatCri-du-Chat

• InversionInversion – Alters the position and sequence of Alters the position and sequence of

the genes so that gene order is the genes so that gene order is reversedreversed

Changes in Changes in Chromosome StructureChromosome Structure

• DuplicationsDuplications– Occurs when a gene Occurs when a gene

sequence is sequence is in in excess excess of the normal of the normal amount.amount.

Changes in Changes in Chromosome StructureChromosome Structure

• Fragile X syndromeFragile X syndrome

– Mental retardationMental retardation

– Repeats that may block Repeats that may block expression of gene on expression of gene on X chromosomeX chromosome

DuplicationsDuplications

Mistake SummaryMistake Summary

DesignedDesignedbyby

Anne F. MabenAnne F. Maben

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