FundamentalFundamentals of Geneticss of Genetics

Patterns of InheritancePatterns of Inheritance

The History of GeneticsThe History of Genetics GeneticsGenetics – scientific study of heredity – scientific study of heredity TraitTrait – characteristic that can be – characteristic that can be

passed from parents to offspringpassed from parents to offspring

Father of GeneticsFather of Genetics Gregor Mendel Gregor Mendel

(born 1822)(born 1822)Austrian Monk Austrian Monk Studied 7 Studied 7

different pea different pea plant traits that plant traits that are are true-true-breedingbreeding Produce offspring Produce offspring identical to identical to themselvesthemselves

Mendel’s 1Mendel’s 1stst ConclusionConclusion

Biological inheritance is Biological inheritance is passed from one passed from one generation to the next- generation to the next- GenesGenes

AllelesAlleles- different forms of - different forms of a gene a gene

Parental CrossParental CrossCross-pollinated flowers with Cross-pollinated flowers with

opposite traits (tall, short) opposite traits (tall, short) P generationP generation

Plants from the first cross Plants from the first cross were all tall- were all tall- hybridshybrids. . FF11 generation generation

FF11 Cross Cross Allowed plants from P cross Allowed plants from P cross

to self-fertilizeto self-fertilize The recessive trait had The recessive trait had

reappeared!!reappeared!! About 25% of the offspring About 25% of the offspring

(F(F22 generation) were short. generation) were short.

Mendel’s 2Mendel’s 2ndnd ConclusionConclusionPrinciple of DominancePrinciple of Dominance

Some alleles are Some alleles are dominantdominantCapital Letter -R,DCapital Letter -R,DThis trait will be always be seenThis trait will be always be seen

Some alleles are Some alleles are recessiverecessiveLower case Letter –r,dLower case Letter –r,dThis trait will only be seen This trait will only be seen when a dominant allele is NOT when a dominant allele is NOT presentpresent

Mendel’s 3Mendel’s 3rdrd ConclusionConclusion

Principle of SegregationPrinciple of SegregationAlleles separate from each Alleles separate from each

other during formation of sex other during formation of sex cells, or cells, or gametesgametes..

PurebredPurebred – organism receives the – organism receives the same genetic traits form both of its same genetic traits form both of its parentsparents HomozygousHomozygous – AA or aa – AA or aa

HybridHybrid – organism receives – organism receives different forms of a genetic traitdifferent forms of a genetic trait HeterozygousHeterozygous - Aa - Aa

Important TermsImportant Terms

GenesGenes – sections of a chromosome that – sections of a chromosome that code for a traitcode for a trait

AlleleAllele – distinct form of a gene – distinct form of a gene Dominant AlleleDominant Allele – expressed when two – expressed when two

different alleles are present; represented different alleles are present; represented with capital letterwith capital letter

Recessive AlleleRecessive Allele – form of gene that is not – form of gene that is not expressed when paired with a dominant expressed when paired with a dominant allele; represented with lower case letterallele; represented with lower case letter

Genes Represent TraitsGenes Represent Traits

GenotypeGenotype – genes that make up an – genes that make up an organismorganism Includes both genes in a homologous pairIncludes both genes in a homologous pair

PhenotypePhenotype – outward expression of the trait – outward expression of the trait

HomozygousHomozygous – two alleles are identical (AA – two alleles are identical (AA or aa)or aa)

HeterozygousHeterozygous – two alleles are different – two alleles are different (Aa)(Aa) Also known as a hybrid organismAlso known as a hybrid organism

Genetics and Genetics and PredictionPrediction

Predictions for One TraitPredictions for One Trait

ProbabilityProbability – predict likelihood of an – predict likelihood of an event or outcomeevent or outcome

Punnett squarePunnett square – grid for organizing – grid for organizing genetic informationgenetic information Can be used to make predictions about Can be used to make predictions about

a cross between two organsimsa cross between two organsims Monohybrid CrossMonohybrid Cross – cross between two – cross between two

parents and one traitparents and one trait

Monohybrid CrossMonohybrid Cross

Predictions for Two Predictions for Two TraitsTraits

Dihybrid CrossDihybrid Cross – cross between two – cross between two parents and two traitsparents and two traits Use a 4 x 4 Punnett squareUse a 4 x 4 Punnett square Sixteen possible outcomesSixteen possible outcomes

Incomplete DominanceIncomplete Dominance

Heterozygous offspring show a Heterozygous offspring show a phenotype that is in-between the phenotype that is in-between the phenotypes of the two homozygous phenotypes of the two homozygous parentsparents Blending of traitsBlending of traits Color in snapdragons; Color in snapdragons;

instead of white or red, instead of white or red,

color is pinkcolor is pink

CodominanceCodominance

Both alleles are expressed Both alleles are expressed Example: Blood typeExample: Blood type

IIAA, I, IBB, i(O), or I, i(O), or IAAIIBB blood type blood type Both A and B are dominant so they are Both A and B are dominant so they are

both expressed in the Iboth expressed in the IAAIIBB blood type blood type

Polygenic TraitPolygenic Trait

Trait controlled by more than Trait controlled by more than one geneone gene Example: eye colorExample: eye color

PleiotropyPleiotropy

Single gene affects Single gene affects more than one traitmore than one trait

Example: sickle cell Example: sickle cell anemiaanemia

Effects include Effects include blood cell shape, blood cell shape, anemia, anemia, weakness, brain weakness, brain damage, spleen damage, spleen damage, and damage, and heart damageheart damage

Environmental EffectsEnvironmental Effects

Phenotype is a combination of Phenotype is a combination of genetic and environmental genetic and environmental influencesinfluences Example: Himalayan rabbit – fur Example: Himalayan rabbit – fur

color depends on body color depends on body temperaturetemperature

Human Human GeneticsGenetics

Difficulties in Studying Difficulties in Studying Human HeredityHuman Heredity

Controlled Controlled experiments are experiments are not possiblenot possible

Small numbers Small numbers of offspring per of offspring per generationgeneration

Long periods Long periods between between generationsgenerations

Sex DeterminationSex Determination

Autosomes – body chromosomes – first Autosomes – body chromosomes – first 22 pair22 pair

Same in both male and femaleSame in both male and female

Sex Chromosomes – 1 pair, last pairSex Chromosomes – 1 pair, last pair

XX – FemaleXX – Female

XY - MaleXY - Male

X X

X XX

Y

XX XX

XY XY

XX = 50%XY = 50%

You always have a 50% chance of having a girl and a 50% chance of having a boy!

Sex Linked TraitsSex Linked Traits

Traits controlled by recessive genes Traits controlled by recessive genes located on sex chromosomes (normally located on sex chromosomes (normally associated with the X chromosome)associated with the X chromosome)

HemophiliaHemophilia – blood clotting enzyme – blood clotting enzyme

is absentis absent Queen Victoria’s family affectedQueen Victoria’s family affected

Sex Linked TraitsSex Linked Traits

Red – Green ColorblindnessRed – Green Colorblindness – individuals – individuals cannot distinguish between these two cannot distinguish between these two colorscolors

Sex Linked TraitsSex Linked Traits

Duchene Duchene Muscular Muscular DystrophyDystrophy – – wasting away wasting away of skeletal of skeletal musclemuscle

XR

Xr

XR

XR XR

XR Xr

Y

XR Y

Xr Y

XR

Xr

Xr

XR Xr

Xr Xr

Y

XR Y

Xr Y

Females•XRXR = normal•XRXr = carrier•XrXr = disease

Males•XRY = normal•XrY = disease

Sex – Limited TraitsSex – Limited Traits

Controlled by genes located in the Controlled by genes located in the autosomesautosomes

Only expressed in the presence of Only expressed in the presence of sex hormonesex hormone

Only expressed in one genderOnly expressed in one gender First seen at puberty (hormones First seen at puberty (hormones

produced in large enough produced in large enough quantitiesquantities

Sex – Limited TraitsSex – Limited Traits

Examples:Examples: Male bird’s Male bird’s

colorful colorful plumageplumage

Beard growth Beard growth in malesin males

Milk Milk production in production in femalesfemales

Sex Influenced TraitsSex Influenced Traits

Traits that are caused by a gene whose Traits that are caused by a gene whose expression differs in males and femalesexpression differs in males and females

Also located on autosomesAlso located on autosomes Expressed in the presence of male or Expressed in the presence of male or

female hormonesfemale hormones Example: male pattern baldnessExample: male pattern baldness

BB = normalBB = normal Bb = males bald, females normalBb = males bald, females normal bb = males and females baldbb = males and females bald

Hereditary DisordersHereditary Disorders

Techniques for detecting genetic Techniques for detecting genetic disordersdisorders AmniocentesisAmniocentesis – technique used that – technique used that

removes and studies amniotic fluid removes and studies amniotic fluid

during pregnancy; during pregnancy; identifies only identifies only

chromosomal disorderschromosomal disorders

Hereditary DisordersHereditary Disorders

KaryotypingKaryotyping – an – an enlarged photo of enlarged photo of the chromosome the chromosome pairs (map) to pairs (map) to identify any identify any abnormalities in abnormalities in the chromosomesthe chromosomes

Chromosomal Chromosomal DisordersDisorders

Chromosomes fail to Chromosomes fail to separate during meiosisseparate during meiosis

Nondisjuction-abnormal Nondisjuction-abnormal numbers of chromosomes numbers of chromosomes enter gametesenter gametes

Pedigree ChartsPedigree Charts

Chart which shows how a trait and the Chart which shows how a trait and the genes that control it are inherited genes that control it are inherited within a familywithin a family

Identifies the presence or absence of Identifies the presence or absence of particular trait in members of each particular trait in members of each generationgeneration

Pedigree ChartsPedigree Charts Males = Males = Females = Females = Generations = Roman NumeralsGenerations = Roman Numerals Individuals = Numbered sequentiallyIndividuals = Numbered sequentially Trait Expressed = Filled inTrait Expressed = Filled in Non Carriers = EmptyNon Carriers = Empty Carrier (not ill) = Half filledCarrier (not ill) = Half filled

Individual who carries a recessive allele Individual who carries a recessive allele that is not expressedthat is not expressed