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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