Genetics & InheritanceGenetics & Inheritance

Gregor MendelGregor Mendel• Father of GeneticsFather of Genetics

• worked in a monasteryworked in a monastery

• Studied how traits were Studied how traits were passed from parents to passed from parents to offspringoffspring

Experimental ApproachExperimental Approach• Chose Chose garden garden

peas peas becausebecause::

– Self-fertilizingSelf-fertilizing

– True-breedingTrue-breeding

Experimental Experimental ApproachApproach

• self-pollinatedself-pollinated • cross-pollinatedcross-pollinated

by human by human manipulation manipulation btwn two diff. btwn two diff. plantsplants

• Mendel cross-fertilized Mendel cross-fertilized true-true-breeding garden pea plantsbreeding garden pea plants having having clearly contrasting traitsclearly contrasting traits

Mendel’s ExperimentMendel’s Experiment

1. P Generation1. P Generation• Self-pollinatedSelf-pollinated for several generations for several generations

to get “true-breeding”to get “true-breeding”• Always produce offspring w/ the Always produce offspring w/ the

desired traitdesired trait2. F2. F11 Generation Generation

• Cross-pollinated P individuals with Cross-pollinated P individuals with contrasting traitscontrasting traits

• purple X whitepurple X white

3. F3. F22 Generation Generation

• Self-pollinated an Self-pollinated an F1 individualF1 individual

• purple X purplepurple X purple

Mendel Wondered:Mendel Wondered:

Why does one form of the trait Why does one form of the trait disappeardisappear in the in the

first generation (first generation (FF11 ), ),

only to only to show upshow up in the in the second generation (second generation (FF2 2 )??)??

Some Terms Used In GeneticsSome Terms Used In Genetics

• Dominant (G)Dominant (G): When present, : When present, “masks” the other trait“masks” the other trait

• Recessive (g):Recessive (g): Has no effect on the Has no effect on the organism when the dominant allele organism when the dominant allele is presentis present

Genetic Genetic TermsTerms

Basic GeneticsBasic Genetics• Observable characters are the result of Observable characters are the result of

genesgenes that come in slightly different that come in slightly different molecular forms called molecular forms called allelesalleles..

Genetic ConceptsGenetic Concepts• GenotypeGenotype is the is the alleles presentalleles present

(I.e. Aa, or aa) (this individuals “genetic (I.e. Aa, or aa) (this individuals “genetic makeup”makeup”

• PhenotypePhenotype is is

what you seewhat you see

(I.e. brown, tall) (I.e. brown, tall)

Some Terms Used In GeneticsSome Terms Used In Genetics• HomozygousHomozygous = alleles are the same = alleles are the same– dominant =“AA” dominant =“AA”

–recessive = “aa”recessive = “aa”

• HeterozygousHeterozygous = alleles differ (“Aa”). = alleles differ (“Aa”).– One allele is One allele is dominantdominant ( (AA))

–Second allele is Second allele is recessiverecessive ( (aa))

º Dominant allele Dominant allele blocks expressionblocks expression of recessive productof recessive product

ProbabilityProbability• Likelihood that a specific event will Likelihood that a specific event will

occuroccur• May be expressed at fraction, decimal, May be expressed at fraction, decimal,

percent or ratiopercent or ratio• Every time an event happens it has Every time an event happens it has

equal probability of happening - equal probability of happening - regardless of # of times it has regardless of # of times it has happened beforehappened before

Predicting results of Predicting results of monohybrid crossmonohybrid cross

• Use a punnett Use a punnett squaresquare

• Tracks only Tracks only one traitone trait

Phenotypic/Genotypic Phenotypic/Genotypic RatiosRatios

• Phenotypic: Dominant:recessive (3:1)Phenotypic: Dominant:recessive (3:1)

• Genotypic: HH:Hh:hh (1:2:1) or Genotypic: HH:Hh:hh (1:2:1) or (1HH:2Hh:1hh)(1HH:2Hh:1hh)

• Totals must equal # of boxes in Totals must equal # of boxes in punnett squarepunnett square

Punnett SquaresPunnett Squares

• Dihybrid cross: examines 2 traits Dihybrid cross: examines 2 traits togethertogether

TestcrossTestcross• Cross an individual w/ an unknown genotype Cross an individual w/ an unknown genotype

(dominant pheno) w/ a homozygous (dominant pheno) w/ a homozygous recessive - if any offspring are recessive, the recessive - if any offspring are recessive, the unknown must be heterozygousunknown must be heterozygous

• Plant produces all purple flowers, what is its Plant produces all purple flowers, what is its genotype? PP or Pp?genotype? PP or Pp?

P P P pP P P p

p Pp Pp p Pp pp p Pp Pp p Pp pp

p Pp Pp p Pp ppp Pp Pp p Pp pp

Complete DominanceComplete Dominance

• Dominant allele Dominant allele completely maskscompletely masks the expression of anotherthe expression of another

–Heterozygous and homozygous Heterozygous and homozygous dominant individuals show same dominant individuals show same phenotype phenotype

XX

Incomplete DominanceIncomplete Dominance• Dominant allele Dominant allele

cannot completely cannot completely maskmask the expression the expression of anotherof another

• Have intermediate Have intermediate phenotypephenotype–Example: Example: redred

snapdragons snapdragons crossed with crossed with whitewhite ones yield ones yield pinkpink..

CodominanceCodominance

– A A whitewhite horse and a horse and a blackblack horse horse produce horses with black produce horses with black andand white white hairs – both alleles are expressedhairs – both alleles are expressed

–Roan horse:Roan horse:

• Controlled by 3 + alleles of a geneControlled by 3 + alleles of a gene

• Ex: Blood TypesEx: Blood Types

• PhenotypePhenotype GenotypeGenotype

AA IIAAIIAA or I or IAAii BB IIBBIIBB or I or IBBii

ABAB I IAAIIBB

OO iiii

Multiple AllelesMultiple Alleles

Single Allele TraitsSingle Allele Traits• Cystic fibrosisCystic fibrosis

• Hair on third Hair on third knuckleknuckle

• Earlobe Earlobe attachmentattachment

• Tongue rollingTongue rolling

Polygenic TraitsPolygenic Traits• Characteristic controlled by several Characteristic controlled by several

genesgenes– skin, hair, eye colorskin, hair, eye color

Complex CharactersComplex Characters• Influenced by genes & environmentInfluenced by genes & environment–Polygenic traitsPolygenic traits

–Height, heart disease cancerHeight, heart disease cancer

Effect of Gene LocationEffect of Gene Location• Sex-linked genes & traitsSex-linked genes & traits–X LinkedX Linked• Traits found only on the X Traits found only on the X

chromosomechromosome• Males get only 1 allele because they Males get only 1 allele because they

have only 1 Xhave only 1 X• HemophiliaHemophilia• Colorblindness (recessive)Colorblindness (recessive)• ALD (Lorenzo’s oil)ALD (Lorenzo’s oil)

Sex-linked traitsSex-linked traits

Dihybrid CrossDihybrid Cross

• Predict results of 2 traitsPredict results of 2 traits

Dihybrid CrossDihybrid Cross

Sex Chromosomes & AutosomesSex Chromosomes & Autosomes• Sex C’some determine gender Sex C’some determine gender – Male = XY, Female = XXMale = XY, Female = XX

• Autosomes: all other c’somesAutosomes: all other c’somes

Male & Female KaryotypesMale & Female Karyotypes

Mendel's Mendel's Law of SegregationLaw of Segregation

• Diploid organisms inherit two genes Diploid organisms inherit two genes per traitper trait• A pair of factors (alleles) is segregated A pair of factors (alleles) is segregated

or separated during the formation of or separated during the formation of gametes (meiosis – anaphase II) so gametes (meiosis – anaphase II) so sperm or egg only carry one allele for sperm or egg only carry one allele for each traiteach trait• If mom is Aa..you either get A or a If mom is Aa..you either get A or a

Law of Independent Law of Independent AssortmentAssortment

• Factors for different characteristics are Factors for different characteristics are distributed to gametes independently of distributed to gametes independently of one anotherone another

• Only true for genes on separate c’somes or Only true for genes on separate c’somes or far apart on same c’somefar apart on same c’some

• Ex: white flowers and smooth pods are Ex: white flowers and smooth pods are independent of each other OR dimples and independent of each other OR dimples and skin color are independent of each otherskin color are independent of each other

Mutations= Ch 12Mutations= Ch 12• Change in a geneChange in a gene–may be due to copying incorrectly or may be due to copying incorrectly or

damageddamaged

• Most are recessiveMost are recessive• Can be good, bad, or have no effectCan be good, bad, or have no effect• Somatic ones (body cells) affect only Somatic ones (body cells) affect only

the organismthe organism• If occurs in germ cell (If occurs in germ cell (gametesgametes), may ), may

be passed to offspringbe passed to offspring

Chromosome MutationsChromosome Mutations• DeletionDeletion - lose a piece of c’some - lose a piece of c’some• InversionInversion - a piece flips around - a piece flips around• TranslocationTranslocation - piece of c’some attaches - piece of c’some attaches

itself to a different c’someitself to a different c’some• non-disjunctionnon-disjunction - homologues don’t - homologues don’t

separate during meiosisseparate during meiosis– Trisomy 21 = Trisomy 21 = Down SyndromeDown Syndrome …..47X …..47X–XXY = XXY = Klinefelters SyndromeKlinefelters Syndrome in males in males

(feminine, infertile)…..47X(feminine, infertile)…..47X–X = X = TurnersTurners (female but infertile) (female but infertile)

….monosomy….45X….monosomy….45X

Chromosome MutationsChromosome Mutations

• Klinefelters Klinefelters

• Turner SyndromeTurner Syndrome

Gene MutationsGene Mutations

Gene MutationsGene Mutations• Involve Involve one or more nucleotidesone or more nucleotides in a strand in a strand

of DNA (not whole chromosome)of DNA (not whole chromosome)

• Point mutations-ONE errorPoint mutations-ONE error– SubstitutionSubstitution

• THE DOG BIT THE CATTHE DOG BIT THE CAT• THE DOG BIT THE CARTHE DOG BIT THE CAR

• Sickle Cell anemiaSickle Cell anemia: subs A for T : subs A for T defective hemoglobindefective hemoglobin

– Deletion-deletes a nucleotideDeletion-deletes a nucleotide• THE CAT ATE THE FAT RATTHE CAT ATE THE FAT RAT

• THE ATA TET HEF ATR ATTTHE ATA TET HEF ATR ATT

– Insertion-inserts a nucleotideInsertion-inserts a nucleotide• THE CAT ATE THE FAT RATTHE CAT ATE THE FAT RAT

• THE CAT ATE THE FAT RATS THE CAT ATE THE FAT RATS

• Both cause frameshift mutationsBoth cause frameshift mutations!!

Gene MutationsGene Mutations

• Frameshift - Frameshift - throws off throws off entire entire sequence…sequence…

caused by caused by deletions or deletions or additionsadditions

Detecting Genetic DisordersDetecting Genetic Disorders• Genetic screeningGenetic screening: examines your genetic : examines your genetic

makeup & potential risk of passing makeup & potential risk of passing disorders to offspring followed by disorders to offspring followed by genetic genetic counselingcounseling to discuss results to discuss results

• Before Birth on fetusBefore Birth on fetus– AmniocentesisAmniocentesis: analyze amniotic fluid looks : analyze amniotic fluid looks

at fetal cells, proteins, do karyotypeat fetal cells, proteins, do karyotype– Chorionic Villi SamplingChorionic Villi Sampling (CVS): from tissue (CVS): from tissue

between placenta & fetus, do karyotypebetween placenta & fetus, do karyotype

Treating Genetic DisordersTreating Genetic Disorders• Symptom-relievingSymptom-relieving– Ex: insulin injections for diabeticEx: insulin injections for diabetic

• Gene TherapyGene Therapy– Replace defective gene w/ copy of a healthy Replace defective gene w/ copy of a healthy

oneone• Somatic cell therapy alters only body cellsSomatic cell therapy alters only body cells• Germ cell therapy alters sperm or eggGerm cell therapy alters sperm or egg

Linkage groupsLinkage groups

• Genes located on the same Genes located on the same c’some are linked c’some are linked

• You inherit them together - unless You inherit them together - unless crossing over separates them= crossing over separates them= chromosome mapschromosome maps

CrossingCrossing Over Over

• The further The further apart two genes apart two genes are from each are from each other on the other on the c’some the c’some the likelier they are likelier they are to be separated to be separated by crossoversby crossovers

Genetic Genetic DisordersDisorders

Male - has trait Male- doesn’t have trait

Female - has trait Female - doesn’t have traitFemale - carrier

Male - carrier

PedigreesPedigrees• Way of tracing traits through a familyWay of tracing traits through a family

• Carrier: doesn’t express trait, but Carrier: doesn’t express trait, but can pass it on to offspringcan pass it on to offspring

Pedigree for Cystic FibrosisPedigree for Cystic Fibrosis