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


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


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)


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)


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


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.


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


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)

http://en.wikipedia.org/wiki/Image:Earlobes_free_attached.jpg

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


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?


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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

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

Observing Patterns in Inherited Traits

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