Download - Observing Patterns in Inherited Traits
Observing Patterns Observing Patterns in Inherited Traitsin Inherited Traits
Chapter 13Chapter 13
Terms and ConceptsTerms and Concepts
GeneGene Heritable unit of information about traitsHeritable unit of information about traits One gene generally codes for one proteinOne gene generally codes for one protein In a diploid cell there are pairs of genesIn a diploid cell there are pairs of genes
One of the pair on each of the homologous One of the pair on each of the homologous chromosomeschromosomes
LocusLocus Location of a gene on the chromosomeLocation of a gene on the chromosome
Terms and ConceptsTerms and Concepts
AlleleAllele Different molecular forms or traits of the Different molecular forms or traits of the
same genesame gene Arise by mutationArise by mutation
A permanent change in a gene and in the A permanent change in a gene and in the information it carriesinformation it carries
Diploid cells have two alleles for each Diploid cells have two alleles for each genegene
Terms and ConceptsTerms and Concepts
Types of allelesTypes of alleles DominantDominant
Its trait is always expressedIts trait is always expressed Masks the effect of a recessive allele Masks the effect of a recessive allele Represented with a capital letter in inheritance problems (A)Represented with a capital letter in inheritance problems (A)
RecessiveRecessive Expressed only when paired with another identical recessive Expressed only when paired with another identical recessive
alleleallele Its trait is masked by dominant allelesIts trait is masked by dominant alleles Represented with a lower case letter in inheritance Represented with a lower case letter in inheritance
problems (a)problems (a)
Terms and ConceptsTerms and Concepts
Combinations of allelesCombinations of alleles Homozygous conditionHomozygous condition
Homologs carry the same alleleHomologs carry the same allele A pair of identical alleles belong to a true-breeding A pair of identical alleles belong to a true-breeding
lineagelineage Individuals can be either homozygous recessive (aa) or Individuals can be either homozygous recessive (aa) or
homozygous dominant (AA)homozygous dominant (AA) Heterozygous conditionHeterozygous condition
Homologs carry different allelesHomologs carry different alleles Individuals are referred to as heterozygous (Aa) or Individuals are referred to as heterozygous (Aa) or
hybrids (result of a cross between two different true-hybrids (result of a cross between two different true-breeding individuals)breeding individuals)
Terms and ConceptsTerms and Concepts
Gene expressionGene expression Process by which a gene’s information is Process by which a gene’s information is
converted to a structural or functional converted to a structural or functional part of a cellpart of a cell
Transcription of DNA to mRNATranscription of DNA to mRNA Translation of RNA to proteinTranslation of RNA to protein
Determines traitsDetermines traits
Terms and ConceptsTerms and Concepts
GenotypeGenotype Particular alleles that an individual carriesParticular alleles that an individual carries Examples: AA, Aa, aaExamples: AA, Aa, aa
PhenotypePhenotype Refers to an individual’s traitsRefers to an individual’s traits Examples: color, shape, size, texture, etc.Examples: color, shape, size, texture, etc.
Terms and ConceptsTerms and Concepts
Genetic crossesGenetic crosses Two individuals are crossed and the Two individuals are crossed and the
resulting offspring are examined to resulting offspring are examined to determine inheritance patternsdetermine inheritance patterns
P stands for the parentsP stands for the parents FF11 stands for the first-generation offspring stands for the first-generation offspring
of crossed P individualsof crossed P individuals FF22 stands for the second-generation stands for the second-generation
offspring of intercrossed Foffspring of intercrossed F11 individuals individuals
QuestionsQuestions
GeneGene An individual’s traitsAn individual’s traits LocusLocus HeterozygousHeterozygous Dominant alleleDominant allele Second generation offspringSecond generation offspring True-breedingTrue-breeding HomozygousHomozygous HybridsHybrids An individual’s genesAn individual’s genes GenotypeGenotype A trait that is always A trait that is always
expressedexpressed PhenotypePhenotype Heritable unit of informationHeritable unit of information F2 generationF2 generation Location of a geneLocation of a gene
Genetic CrossesGenetic Crosses
The following slides will present a The following slides will present a genetic cross demonstrating genetic cross demonstrating the use of the above terminologythe use of the above terminology and the use of punnett squaresand the use of punnett squares
Genetic CrossesGenetic Crosses
Whether a person has attached or Whether a person has attached or detached earlobes depends on a detached earlobes depends on a single gene with two alleles single gene with two alleles (We can (We can name the gene with a letter “e”)name the gene with a letter “e”) Dominant allele is detached ear lobesDominant allele is detached ear lobes
Referred to as E (capital for dominant)Referred to as E (capital for dominant) Recessive allele is attached ear lobesRecessive allele is attached ear lobes
Referred to as e (lower case for recessive)Referred to as e (lower case for recessive)
Genetic CrossesGenetic Crosses Each individual inherits one allele from each Each individual inherits one allele from each
parent parent Depending on what combination of alleles are Depending on what combination of alleles are
inherited will determine the genotype and inherited will determine the genotype and phenotype of the individualphenotype of the individual Inherit two dominant allelesInherit two dominant alleles
Genotype = EE or homozygous dominantGenotype = EE or homozygous dominant Phenotype = detached earlobesPhenotype = detached earlobes
Inherit two recessive allelesInherit two recessive alleles Genotype = ee or homozygous recessiveGenotype = ee or homozygous recessive Phenotype = attached earlobesPhenotype = attached earlobes
Inherit one dominant allele and one recessive alleleInherit one dominant allele and one recessive allele Genotoype = Ee or heterozygousGenotoype = Ee or heterozygous Phenotype = detached earlobes Phenotype = detached earlobes
The dominant allele will always mask the recessive allele’s traitThe dominant allele will always mask the recessive allele’s trait
Genetic CrossesGenetic Crosses
Punnett squares can be used to determine Punnett squares can be used to determine the probability of the genotypes and the probability of the genotypes and phenotypes of offspring of any given cross phenotypes of offspring of any given cross such as the followingsuch as the following
If we crossed a homozygous dominant dad If we crossed a homozygous dominant dad with a homozygous recessive mom, what with a homozygous recessive mom, what would the offspring genotype(s) and would the offspring genotype(s) and phenotype(s) be?phenotype(s) be?
Genetic CrossesGenetic Crosses
First you need to determine the First you need to determine the genotype of the parentsgenotype of the parents Dad = homozygous dominant = EEDad = homozygous dominant = EE Mom = homozygous recessive = eeMom = homozygous recessive = ee
Genetic CrossesGenetic Crosses
Second, determine what each parent’s gametes Second, determine what each parent’s gametes will bewill be Based on what we know about meiosis we can Based on what we know about meiosis we can
determine what allele the gametes will carry (see determine what allele the gametes will carry (see figure 10.5)figure 10.5)
Remember that during meiosis homologous pairs are Remember that during meiosis homologous pairs are separated (anaphase I). One of the two alleles is on one of separated (anaphase I). One of the two alleles is on one of the homologs, the other is on the other homolog. Therefore, the homologs, the other is on the other homolog. Therefore, during meiosis one “E” will segregate into one gamete, while during meiosis one “E” will segregate into one gamete, while the other “E” will segregate into the other gametethe other “E” will segregate into the other gamete
Dad’s gametes will be E and EDad’s gametes will be E and E Mom’s gametes will be e and eMom’s gametes will be e and e
Genetic CrossesGenetic Crosses
Third, place the gametes in a Third, place the gametes in a punnett squarepunnett square Dad’s go vertically in the first columnDad’s go vertically in the first column Mom’s go horizontally across the topMom’s go horizontally across the top
ee ee
EE
EE
Genetic CrossesGenetic Crosses
Fourth, determine what the possible Fourth, determine what the possible outcomes are if either of dad’s outcomes are if either of dad’s gametes fuses with either of mom’s gametes fuses with either of mom’s eggseggs
ee ee
EE EeEe EeEe
EE EeEe EeEe
Genetic CrossesGenetic Crosses
Fifth, determine the probability of the Fifth, determine the probability of the genotypes and phenotypesgenotypes and phenotypes Genotype possibilities areGenotype possibilities are
EE, Ee, or eeEE, Ee, or ee Count up how many out of four of each Count up how many out of four of each
combination are in the punnett squarecombination are in the punnett square
EE : Ee : eeEE : Ee : ee
0 : 4 : 00 : 4 : 0
Answer
Genetic CrossesGenetic Crosses
Fifth, determine the probability of the Fifth, determine the probability of the genotypes and phenotypesgenotypes and phenotypes Phenotype possibilities arePhenotype possibilities are
Detached or AttachedDetached or Attached Count up how many out of the four of each Count up how many out of the four of each
trait are in the punnett squaretrait are in the punnett square
Detached : AttachedDetached : Attached
4 : 04 : 0
Answer
Genetic CrossesGenetic Crosses
Punnett Square PracticePunnett Square Practice Cross a heterozygous dad with a homozygous Cross a heterozygous dad with a homozygous
dominant momdominant mom Ee X EEEe X EE
Cross a heterozygous dad with a Cross a heterozygous dad with a heterozygous momheterozygous mom
Ee X EeEe X Ee Cross a homozygous recessive dad with a Cross a homozygous recessive dad with a
heterozygous momheterozygous mom ee x Eeee x Ee
Gregor MendelGregor Mendel
Using pea plants Gregor Mendel Using pea plants Gregor Mendel determined inheritance patternsdetermined inheritance patterns Pea plants are self-fertilizing and so Pea plants are self-fertilizing and so
develop “true-breeding” varieties develop “true-breeding” varieties (homozygous)(homozygous)
Mendel could open a floral bud of a true-Mendel could open a floral bud of a true-breeding plant and snip out its anthers breeding plant and snip out its anthers (contains pollen grains). The buds can (contains pollen grains). The buds can then be brushed with pollen from a then be brushed with pollen from a different true-breeding plant.different true-breeding plant.
Following observable differences Following observable differences between plants Mendel predicted that he between plants Mendel predicted that he would be able to follow certain traits and would be able to follow certain traits and see if there were patterns in its see if there were patterns in its inheritance.inheritance.
Fig. 10-3, p.154
Gregor MendelGregor Mendel
Theory of SegregationTheory of Segregation Diploid cells have pairs of genes, on Diploid cells have pairs of genes, on
pairs of homologous chromosomespairs of homologous chromosomes The two genes of each pair are The two genes of each pair are
separated from each other during separated from each other during meiosis, so they end up in different meiosis, so they end up in different gametesgametes
Mendel used monohybrid crosses to Mendel used monohybrid crosses to demonstrate segregationdemonstrate segregation
Gregor Mendel: Monohybrid Gregor Mendel: Monohybrid CrossCross
Pea flower colorPea flower color Cross 1Cross 1
True-breeding purple flowering plants were crossed True-breeding purple flowering plants were crossed with true-breeding white flowering plants (these are with true-breeding white flowering plants (these are the parental generation, P)the parental generation, P)
The offspring or FThe offspring or F11 generation were all purple generation were all purple floweringflowering
Cross 2Cross 2 The FThe F11 generation were allowed to self-fertilize generation were allowed to self-fertilize The offspring or FThe offspring or F22 generation had a ratio of 3 purple generation had a ratio of 3 purple
flowering plants to 1 white flowering plantflowering plants to 1 white flowering plant
Gregor Mendel: Monohybrid Gregor Mendel: Monohybrid CrossCross
Pea flower colorPea flower color Mendel was able to infer thatMendel was able to infer that
Both parents must have two “units” of Both parents must have two “units” of informationinformation
Each parent transferred one of their “units” Each parent transferred one of their “units” of information to the offspringof information to the offspring
The purple color dominated the white colorThe purple color dominated the white color The recessive white color shows up in ¼ of The recessive white color shows up in ¼ of
the Fthe F22 generation generation
fertilization produces heterozygous offspring
meiosis II
meiosis I
(chromosomes duplicated
before meiosis)
Homozygous dominant
parent
Homozygous recessive
parent
(gametes) (gametes)
Fig. 10-5, p.156
Gregor Mendel: Monohybrid Gregor Mendel: Monohybrid CrossCross
Pea flower colorPea flower color Purple is dominant = APurple is dominant = A White is recessive = aWhite is recessive = a GenotypesGenotypes
True-breeding purple genotype = AATrue-breeding purple genotype = AA True-breeding white genotype = aaTrue-breeding white genotype = aa
Punnett square for cross 1Punnett square for cross 1
aa aa
AA AaAa AaAa
AA AaAa AaAa
Fig. 10-7b, p.157
Gregor Mendel: Monohybrid Gregor Mendel: Monohybrid CrossCross
Pea flower colorPea flower color FF11 are allowed to self-fertilize are allowed to self-fertilize Punnett square for cross 2Punnett square for cross 2
AA aa
AA AAAA AaAa
aa AaAa aaaa
Fig. 10-7c, p.157
Fig. 10-6, p.156
Gregor MendelGregor Mendel
Test crossTest cross A method of determining genotypeA method of determining genotype To determine the genotype of the FTo determine the genotype of the F11 purple-flowering purple-flowering
plants plants (could be AA or Aa)(could be AA or Aa) Mendel could cross them with Mendel could cross them with true-breeding white-flowered plants true-breeding white-flowered plants (aa)(aa)
If the FIf the F11 is AA, then all of the flowers would be purple is AA, then all of the flowers would be purple If the FIf the F11 is Aa, then half of the flowers would be is Aa, then half of the flowers would be
purple and half whitepurple and half white
Try the crosses on a punnett squareTry the crosses on a punnett square
Gregor MendelGregor Mendel
Theory of Independent AssortmentTheory of Independent Assortment As meiosis ends, genes on pairs of As meiosis ends, genes on pairs of
homologous chromosomes have been homologous chromosomes have been sorted out for distribution into one sorted out for distribution into one gamete or another, independently of gamete or another, independently of gene pairs on other chromosomesgene pairs on other chromosomes
This is due to random alignment during This is due to random alignment during meiosismeiosis
Gregor MendelGregor Mendel
Theory of Independent AssortmentTheory of Independent Assortment Mendel used dihybrid crosses to explain Mendel used dihybrid crosses to explain
how two pairs of genes are sorted into how two pairs of genes are sorted into gametes independentlygametes independently
The following slides will demonstrate the The following slides will demonstrate the type of dihybrid crosses usedtype of dihybrid crosses used
Gregor Mendel: Dihybrid Gregor Mendel: Dihybrid CrossCross
Pea flower color AND plant heightPea flower color AND plant height Cross 1Cross 1
True-breeding purple flowering tall plants were crossed True-breeding purple flowering tall plants were crossed with true-breeding white flowering dwarf plants (these with true-breeding white flowering dwarf plants (these are the parental generation, P)are the parental generation, P)
The offspring of FThe offspring of F11 generation were all purple flowering generation were all purple flowering talltall
Mendel’s question was whether purple flowering would Mendel’s question was whether purple flowering would always be linked to tall or whether purple could go with always be linked to tall or whether purple could go with dwarf and white with tall. Looking at the Fdwarf and white with tall. Looking at the F22 generation generation from cross 2 answered his question.from cross 2 answered his question.
Fig. 10-8, p.158
One of two possible alignments
The only other possible alignment
c Possiblecombinationsof alleles ingametes:
b The resultingalignments atmetaphase II:
a Chromosomealignments atmetaphase I:
A
a
AB Abab aB
a
aa
a abb
b b
b
b
A A
AA
b b
A A B B
BB
B B
aa
aa
aa
b
b
bbB
BB
B B
B
AA
AA
Gregor Mendel: Dihybrid Gregor Mendel: Dihybrid CrossCross
Pea flower color AND plant heightPea flower color AND plant height Cross 2Cross 2
The FThe F11 generation were allowed to self-fertilize generation were allowed to self-fertilize The offspring or FThe offspring or F22 generation had a ratio of generation had a ratio of
9 purple flowering tall plants 9 purple flowering tall plants 3 purple flowering dwarf plants3 purple flowering dwarf plants 3 white flowering tall plants3 white flowering tall plants 1 white flowering dwarf plant1 white flowering dwarf plant
Gregor Mendel: Dihybrid Gregor Mendel: Dihybrid CrossCross
Pea flower color AND plant heightPea flower color AND plant height Mendel was able to infer thatMendel was able to infer that
Purple was not linked to tall and white was Purple was not linked to tall and white was not linked to dwarfnot linked to dwarf
The two different genes did in fact sort The two different genes did in fact sort independentlyindependently
Gregor Mendel: Dihybrid Gregor Mendel: Dihybrid CrossCross
Pea flower color AND plant heightPea flower color AND plant height Purple = APurple = A andand white = awhite = a Tall = BTall = B andand dwarf = bdwarf = b GenotypesGenotypes
True-breeding purple tall genotype = AABBTrue-breeding purple tall genotype = AABB True-breeding white dwarf genotype = aabbTrue-breeding white dwarf genotype = aabb
Punnett square for cross 1Punnett square for cross 1
abab abab
ABAB AaBbAaBb AaBbAaBb
ABAB AaBbAaBb AaBbAaBb
Gregor Mendel: Dihybrid Gregor Mendel: Dihybrid CrossCross
Pea flower color AND heightPea flower color AND height FF11 are allowed to self-fertilize are allowed to self-fertilize
Possible gametes for AaBb arePossible gametes for AaBb are AB, Ab, aB, abAB, Ab, aB, ab
Gregor Mendel: Dihybrid Gregor Mendel: Dihybrid CrossCross
Pea flower color AND plant heightPea flower color AND plant height Punnett square for cross 2Punnett square for cross 2
ABAB AbAb aBaB abab
ABAB AABBAABB AABbAABb AaBBAaBB AaBbAaBb
AbAb AABbAABb AAbbAAbb AaBbAaBb AabbAabb
aBaB AaBBAaBB AaBbAaBb aaBBaaBB aaBbaaBb
abab AaBbAaBb AabbAabb aaBbaaBb aabbaabb
Fig. 10-9, p.159
QuestionsQuestions
T or F: The Theory of Segregation states that the two genes T or F: The Theory of Segregation states that the two genes of each pair stay together during meiosisof each pair stay together during meiosis
What type of cross was used to show Mendel’s Theory of What type of cross was used to show Mendel’s Theory of Segregation?Segregation?
What is a Punnett Square?What is a Punnett Square? What genotype and phenotype ratios are seen in the F2 What genotype and phenotype ratios are seen in the F2
generation?generation? T or F: The Theory of Independent Assortment states that T or F: The Theory of Independent Assortment states that
gene pairs sort independentlygene pairs sort independently What type of cross was used to show Mendel’s Theory of What type of cross was used to show Mendel’s Theory of
Independent Assortment?Independent Assortment? What genotype and phenotype ratios are seen in the F2 What genotype and phenotype ratios are seen in the F2
generation?generation?
Beyond Simple DominanceBeyond Simple Dominance
Mendel studied traits that have clear Mendel studied traits that have clear cut dominant and recessive formscut dominant and recessive forms
Some genes can have alleles that are Some genes can have alleles that are codominant or incompletely codominant or incompletely dominantdominant
Beyond Simple DominanceBeyond Simple Dominance
CodominanceCodominance Non-identical alleles are both fully expressed even in Non-identical alleles are both fully expressed even in
heterozygotesheterozygotes Blood typeBlood type
IIAA and I and IBB alleles are both dominant alleles are both dominant They are always expressedThey are always expressed
i is recessivei is recessive GenotypeGenotype PhenotypePhenotype
IIAAIIAA and I and IAAii Type A bloodType A blood
IIBBIIB B and Iand IBBii Type B bloodType B bloodIIAAIIBB Type AB blood Type AB blood (codominant, they (codominant, they are both expressed)are both expressed)
iiii Type O bloodType O blood
Fig. 10-10, p.160
Beyond Simple DominanceBeyond Simple Dominance
Incomplete dominanceIncomplete dominance One allele isn’t fully dominant over the One allele isn’t fully dominant over the
other allele, so the heterozygote’s other allele, so the heterozygote’s phenotype is somewhere between the phenotype is somewhere between the two homozygotestwo homozygotes
Snapdragon flower colorSnapdragon flower color Red flowers = RRRed flowers = RR White flowers = rrWhite flowers = rr Heterozygotes , Rr are pinkHeterozygotes , Rr are pink
Fig. 10-11, p.160
Beyond Simple DominanceBeyond Simple Dominance
EpistasisEpistasis Some traits are the results of interactions of Some traits are the results of interactions of
two or more gene pairstwo or more gene pairs Labrador coat colorLabrador coat color
Gene encoding pigmentGene encoding pigment black is dominant to brownblack is dominant to brown
Gene encoding deposition of pigmentGene encoding deposition of pigment Dominant allele promotes deposition of pigmentDominant allele promotes deposition of pigment Recessive allele reduces depositionRecessive allele reduces deposition
The two genes work together to determine how much The two genes work together to determine how much of what color pigment ends up in the coatof what color pigment ends up in the coat
Fig. 10-13, p.161
EB Eb eB eb
EB
Eb
eB
eb EeBbblack
EeBBblack
EEBbblack
EEBBblack
EEBbblack
EeBBblack
EeBbblack
Eebbchocolate
EeBbblack
EEbbchocolate
EeBbblack
Eebbchocolate
eeBByellow
eeBbyellow
eebbyellow
eeBbyellow
Fig. 10-12, p.161
Beyond Simple DominanceBeyond Simple Dominance
PleiotropyPleiotropy One gene can influence two or more One gene can influence two or more
traitstraits Marfan syndromeMarfan syndrome
A mutated form of the fibrillin gene affects A mutated form of the fibrillin gene affects the formation of connective tissues, thus its the formation of connective tissues, thus its affects are seen in several areas of the bodyaffects are seen in several areas of the body
Linkage GroupsLinkage Groups
Some alleles tend to be inherited as a groupSome alleles tend to be inherited as a group Mendel’s theory of independent assortment only Mendel’s theory of independent assortment only
works for genes located on different works for genes located on different chromosomeschromosomes
If genes are located on the same chromosome, If genes are located on the same chromosome, then they are generally linkedthen they are generally linked
In some cases crossing over during meiosis will In some cases crossing over during meiosis will separate linked genes depending primarily on separate linked genes depending primarily on how close the two genes are on the chromosomehow close the two genes are on the chromosome
p.162b
Fig. 10-15, p.162
Genes and the EnvironmentGenes and the Environment
Some genes and can be influenced Some genes and can be influenced by the environmentby the environment Temperature affects coat color on Temperature affects coat color on
Himalayan rabbitsHimalayan rabbits Cooler body parts are dark while the main Cooler body parts are dark while the main
body mass is warmer and creating a lighter body mass is warmer and creating a lighter coat colorcoat color
Fig. 10-16, p.163
Fig. 10-17, p.163
Complex Variations in TraitsComplex Variations in Traits
Individuals of populations can show Individuals of populations can show continuous variation in a trait if there continuous variation in a trait if there are multiple genes and are multiple genes and environmental factors that influence environmental factors that influence a traita trait HeightHeight Eye colorEye color Skin colorSkin color
p.164
Fig. 10-19a, p.164
Fig. 10-19b, p.164
Fig. 10-19c, p.164
SummarySummary
Terms and ConceptsTerms and Concepts Genetic CrossesGenetic Crosses MendelMendel
SegregationSegregation Independent AssortmentIndependent Assortment
Beyond simple dominance and other Beyond simple dominance and other variations of inheritance patternsvariations of inheritance patterns