mendel’s genetics. where did that blonde hair come from? law of segregation and random assortment...

Mendel’s GeneticsMendel’s Genetics

Where did that blonde hair come from?Where did that blonde hair come from?law of segregation and random assortmentlaw of segregation and random assortment

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GENETICS and EVOLUTIONGENETICS and EVOLUTION

The purpose of this chapter is to show The purpose of this chapter is to show how genetic traits are passed from one how genetic traits are passed from one generation to another. This is called generation to another. This is called HEREDITYHEREDITY

If there was no genetic variation through If there was no genetic variation through mutation or crossing over of genes there mutation or crossing over of genes there would be no evolutionwould be no evolution

Gregor Mendel The MonasteryGregor Mendel The Monastery

I. Gregor Mendel- the father I. Gregor Mendel- the father of genetics theory (1822-of genetics theory (1822-

1884)1884)A. BackgroundA. Background

1. entered monastery at 211. entered monastery at 21

2. studied math and science2. studied math and science

at University of Viennaat University of Vienna

3. 1857-1865 – investigated3. 1857-1865 – investigated

inheritance in pea plantsinheritance in pea plants

B. Peas – A Fortunate ChoiceB. Peas – A Fortunate Choice (Pisum sagivum)(Pisum sagivum)

1. seven distinct characteristics1. seven distinct characteristics (flower color, flower position,(flower color, flower position, seed color, seed shape, pod seed color, seed shape, pod

shape, pod color, height) shape, pod color, height) 2. easy to grow2. easy to grow 3. mature quickly3. mature quickly 4. easy to pollinate4. easy to pollinate

D. Mendel’s Experiments-D. Mendel’s Experiments- monohybrid monohybrid crosses (one purple & one white parent)crosses (one purple & one white parent)

1. 1. PP11 Generation Generation (Parental) (Parental)

a. crossed plants pure for a trait – a. crossed plants pure for a trait – TRUE- BREEDINGTRUE- BREEDING

2. 2. FF11 Generation Generation (Offsprng of P (Offsprng of P11) a. ) a. all plants show one form of the trait all plants show one form of the trait

3. 3. FF22 Generation Generation (Offsprng of F(Offsprng of F11))

a. show forms of trait in 3:1 a. show forms of trait in 3:1

ratioratio

Mendel’s P, FMendel’s P, F11and Fand F22 Generations Generations

Examples of PExamples of P11 Cross Cross

Tall X ShortTall X Short (both are pure)(both are pure)T T X t tT T X t t

All offspring are tall (T t) FAll offspring are tall (T t) F11 Generation Generation

FF11 Generation (all are hybrids) Generation (all are hybrids)

Purple Flower X Purple Flower X White FlowerWhite Flower (both (both pure)pure) P P X p pP P X p p

All offpsring are purple (Pp) FAll offpsring are purple (Pp) F11 GenerationGeneration

FF11 Generation (all are hybrids) Generation (all are hybrids)

Mendel’s FMendel’s F11 Cross (hybrid x hybrid) Cross (hybrid x hybrid)

Tall X TallTall X Tall (hybrid cross) (hybrid cross)

T t X T tT t X T t

3 tall plants : 1 short plant (F3 tall plants : 1 short plant (F22 Generation) Generation)

Ratio of 3:1Ratio of 3:1

Purple Flowers X Purple FlowersPurple Flowers X Purple Flowers (hybrid) (hybrid) P p X P pP p X P p

3 purple flower plants : 1 white flower (F3 purple flower plants : 1 white flower (F22))

Ratio of 3:1Ratio of 3:1

II. VocabularyII. VocabularyA. DominantA. Dominant (represented by upper (represented by upper

case letter)case letter)

1. allele that masks the recessive1. allele that masks the recessive

allele for the same characteristiallele for the same characteristic c

B. RecessiveB. Recessive (represented by lower (represented by lower

case letter)case letter)

1. allele that is masked by the1. allele that is masked by the

dominant allele for the samedominant allele for the same

characteristic characteristic

II. VocabularyII. Vocabulary

C. C. GenotypeGenotype

1. genetic makeup1. genetic makeup

2. examples 2. examples

a. a. TT, Tt, tt,TT, Tt, tt,

b. b. PP, Pp, ppPP, Pp, pp

D. D. PhenotypePhenotype

1. external appearance1. external appearance

2. examples2. examples

a. tall, shorta. tall, short

b. purple flowers, white flowers b. purple flowers, white flowers

E. E. HomozygousHomozygous (pure) (pure)

1. two alleles code for the same trait 1. two alleles code for the same trait

2. examples 2. examples

a. a. TT, tt, PP, ppTT, tt, PP, pp

F. F. HeterozygousHeterozygous (hybrid)(hybrid)

1. two alleles do not code for the 1. two alleles do not code for the

same traitsame trait

2. examples2. examples

a. a. Tt and PpTt and Pp

III. Complete DominanceIII. Complete Dominance (Monohybrid Cross) (Monohybrid Cross)

A. Both parents are pureA. Both parents are pure 1. homozygous x homozygous1. homozygous x homozygous 2. example 2. example T T x t t T T x t t

B. Both parents are hybridB. Both parents are hybrid 1. heterozygous X heterozygous1. heterozygous X heterozygous 2. example 2. example Tt x TtTt x Tt

III. Complete DominanceIII. Complete Dominance

C. Pure parent X hybrid parentC. Pure parent X hybrid parent1.homozygous dominant X 1.homozygous dominant X

heterozygousheterozygous

a. Example a. Example T T x T t T T x T t 2.homozygous recessive x 2.homozygous recessive x

heterozygousheterozygous

a. Example a. Example tt x Tttt x Tt

PUNNETT SQUARESPUNNETT SQUARES

MENDEL”S THEORYMENDEL”S THEORY

1. Each individual has two copies of an 1. Each individual has two copies of an individual trait -these individual trait -these traits controlled traits controlled by a pair of factorsby a pair of factors

a. today factors are called a. today factors are called allelesalleles 2. There are alternate versions 2. There are alternate versions traitstraits TT = tall tall Tt= tall short tt= short shortTT = tall tall Tt= tall short tt= short short

MENDEL”S THEORYMENDEL”S THEORY

3. One trait may be expressed 3. One trait may be expressed and other may not have an and other may not have an effect.effect.

dominant and recessivedominant and recessive

Analysis of Mendel’s ResultsAnalysis of Mendel’s Results

1. 1. Principle of DominancePrinciple of Dominance

a. one factor (gene) can preventa. one factor (gene) can prevent

expression of another expression of another (dominance)(dominance)

IE: hybrid tall plant – phenotype- tallIE: hybrid tall plant – phenotype- tall

genotype- Ttgenotype- Tt

2. 2. Law of SegregationLaw of Segregation

a. a pair of factors separate a. a pair of factors separate when gametes form when gametes form

3. 3. Law of Independent Law of Independent AssortmentAssortment

a. factors (genes) for differenta. factors (genes) for different

characteristics separatecharacteristics separate

independentlyindependently

WORK ON Inheritance lab WORK ON Inheritance lab

Where did that blonde hair come from?Where did that blonde hair come from?law of segregation and random assortmentlaw of segregation and random assortment

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Incomplete DominanceIncomplete Dominance

The phenotype of an individual is the The phenotype of an individual is the intermediate trait between the two parents:intermediate trait between the two parents:

Or-When two heterozygous genotypes make Or-When two heterozygous genotypes make a third, different phenotype.a third, different phenotype.

EXAMPLES:EXAMPLES: Straight haired mother and curly haired father- the Straight haired mother and curly haired father- the

child will have an intermediate trait such as wavy child will have an intermediate trait such as wavy hairhair

Red snapdragon when crossed with white Red snapdragon when crossed with white snapdragons produce pink snapdragons.snapdragons produce pink snapdragons.

10.5 Do the Mendelian Rules of 10.5 Do the Mendelian Rules of Inheritance Apply to All Traits?Inheritance Apply to All Traits?

In incomplete dominance, the phenotype of In incomplete dominance, the phenotype of the heterozygotes is intermediate between the the heterozygotes is intermediate between the phenotypes of the homozygotesphenotypes of the homozygotes In the genes studied by Mendel, one allele was In the genes studied by Mendel, one allele was

dominant over the other, which was recessivedominant over the other, which was recessive Some alleles, however, are incompletely dominant Some alleles, however, are incompletely dominant

over othersover others When the heterozygous phenotype is intermediate When the heterozygous phenotype is intermediate

between the two homozygous phenotypes, the between the two homozygous phenotypes, the pattern of inheritance is called pattern of inheritance is called incomplete incomplete dominancedominance

10.5 Do the Mendelian Rules of 10.5 Do the Mendelian Rules of Inheritance Apply to All Inheritance Apply to All

Traits?Traits? In incomplete dominance, the phenotype of In incomplete dominance, the phenotype of the heterozygotes is intermediate between the heterozygotes is intermediate between the phenotypes of the homozygotes the phenotypes of the homozygotes (continued)(continued) Human hair texture is influenced by a gene with Human hair texture is influenced by a gene with

two incompletely dominant alleles, two incompletely dominant alleles, HH11 and and HH22

• A person with two copies of the A person with two copies of the HH11 allele has curly hair allele has curly hair

• Someone with two copies of the Someone with two copies of the HH22 allele has straight allele has straight

hairhair

• Heterozygotes (with the Heterozygotes (with the HH11HH22 genotype) have wavy genotype) have wavy

hairhair


In incomplete dominance, the phenotype of In incomplete dominance, the phenotype of the heterozygotes is intermediate between the heterozygotes is intermediate between the phenotypes of the homozygotes the phenotypes of the homozygotes (continued)(continued) If two wavy-haired people marry, their children If two wavy-haired people marry, their children

could have any of the three hair types: curly could have any of the three hair types: curly ((HH11HH11), wavy (), wavy (HH11HH22), or straight (), or straight (HH22HH22))

Figure 10-13 Incomplete dominanceFigure 10-13 Incomplete dominance

H1H2

father

H2

sp

erm

mother

H1 eggs

H1H1 H1H2

H1H2 H2H2

H2

H1

H1H2


A single gene may have multiple allelesA single gene may have multiple alleles An An individualindividual may have at most two different may have at most two different

gene allelesgene alleles A A speciesspecies may have may have multiple allelesmultiple alleles for a given for a given

characteristiccharacteristic• However, each individual still carries two alleles for this However, each individual still carries two alleles for this

characteristiccharacteristic

IV.IV. Incomplete DominanceIncomplete Dominance (both alleles influence the (both alleles influence the

trait)trait)A. Pure X Pure = all hybridsA. Pure X Pure = all hybrids

1.example (red flower and white 1.example (red flower and white flower) a. flower) a. RR x WWRR x WW

B. Hybrid X HybridB. Hybrid X Hybrid

1. e (pink x pink flower)a. 1. e (pink x pink flower)a. RW x RWRW x RW

C. Pure X hybridC. Pure X hybrid

1.ex (red x pink or white x pink)1.ex (red x pink or white x pink)

a. RR x RW or WW x RW a. RR x RW or WW x RW

Incomplete Dominance Four O’clock Incomplete Dominance Four O’clock FlowersFlowers

Pink (RW) White (WW) Pink (RW) White (WW) Red (RR)Red (RR)

Codominant traitsCodominant traits

Both traits are shown – for instance the Both traits are shown – for instance the person with AB blood type is a child with person with AB blood type is a child with one parents that was A blood type and one parents that was A blood type and one parent with B blood type.one parent with B blood type.

Neither trait is dominant. Both are in the Neither trait is dominant. Both are in the genotype and phenotype.genotype and phenotype.

V. Codominance V. Codominance (both alleles are expressed) (both alleles are expressed)

A. Pure X PureA. Pure X Pure

1. example (white horse x red 1. example (white horse x red horse) a. horse) a. WW x RRWW x RR

B. Hybrid x Hybrid B. Hybrid x Hybrid

11.. exampleexample (roan horse x roan (roan horse x roan horse) a. horse) a. RW x RWRW x RW

C. Pure X HybridC. Pure X Hybrid

1. example(redxroan /white xroan)1. example(redxroan /white xroan)

a. a. RR x RW or WW x RWRR x RW or WW x RW

VI. Multiple Allele Problems (Blood VI. Multiple Allele Problems (Blood Types)Types)

A. A. PHENOTYPEPHENOTYPE Type AType A

Type BType B

Type ABType AB

Type OType O

B. B. GENOTYPEGENOTYPE AA, AOAA, AO ( I( IAA I IAA , I , IAA i ) i )

BB, BOBB, BO ( I( IBB I IBB , I , IBB i ) i )

AB AB ( I( IAA I IBB ) )

OOOO ( ii )( ii )

Blood Donors and RecipientsBlood Donors and Recipients

VII. Sex-linked Inheritance VII. Sex-linked Inheritance (X (X linked-carriedlinked-carried

on X chromosome)on X chromosome)

A. Examples of sex-linked traitsA. Examples of sex-linked traits

1. color blindness1. color blindness

2. hemophilia2. hemophilia

3. muscular dystrophy3. muscular dystrophy

4. Icthyosis4. Icthyosis

Individual Individual ChromosomesChromosomes

Normal MaleNormal Male

Male with DiseaseMale with Disease

Normal FemaleNormal Female

Female CarrierFemale Carrier

Female - DiseaseFemale - Disease

X YX Y

X* YX* Y

X XX X

X* XX* X

X* X*X* X*

Problem Solving- Sex Linked DiseasesProblem Solving- Sex Linked Diseases

A. A man is colorblind and his wife is a A. A man is colorblind and his wife is a carrier for colorblindness. What is the carrier for colorblindness. What is the probability that they will have a child who probability that they will have a child who is colorblind? (A son? A daughter?)is colorblind? (A son? A daughter?)

B. A man and woman are both colorblind. B. A man and woman are both colorblind. Can they have a child who is not Can they have a child who is not colorblind?colorblind?

(A son? A daughter?)(A son? A daughter?)

Website –sex linked traitsWebsite –sex linked traits

www.edc./weblabs

http://www.biology.arizona.edu/mendelian_genetics/problem_sets/sex_linked_inheritance/sex_linked_inheritance.html

Pedigree-a genetic family treePedigree-a genetic family treewww.genetics.gsk.com/graphics/autosomal_recessive.gif

htt://

Pedigree chart tells us two thingsPedigree chart tells us two things 1. WHETHER IT IS AN AUTOSOMAL(22 BODY 1. WHETHER IT IS AN AUTOSOMAL(22 BODY

PAIRS) OR SEX-LINKED (1PAIR OF SEX TRAITS PAIRS) OR SEX-LINKED (1PAIR OF SEX TRAITS XX OR XY) If male and female is close to equal it is XX OR XY) If male and female is close to equal it is autosomalautosomal

2. WHETHER IT IS DOM. OR RECESS. TRAIT- IF 2. WHETHER IT IS DOM. OR RECESS. TRAIT- IF THE TRAIT IS PASSED TO NEXT GENERATION – THE TRAIT IS PASSED TO NEXT GENERATION – BUT SKIPPED A GENERATION IT IS RECESSIVE- BUT SKIPPED A GENERATION IT IS RECESSIVE-

IF THE PARENTS WERE NORMAL(WERE IF THE PARENTS WERE NORMAL(WERE CARRIERS) AND HAD A CHILD WITH THE TRAIT IT CARRIERS) AND HAD A CHILD WITH THE TRAIT IT IS RECESSIVEIS RECESSIVE

Autosomal pedigree chartAutosomal pedigree chart

Sex-linked pedigreeSex-linked pedigree

ROYAL FAMILY PEDIGREEROYAL FAMILY PEDIGREE

Dihybrid CrossDihybrid Cross

A cross that involves two traits.A cross that involves two traits.

Example: Example: Predict the results of two pea plants that Predict the results of two pea plants that

are heterozygous for are heterozygous for seed shape – R-round r-wrinkledseed shape – R-round r-wrinkled Seed color- Y- yellow y- greenSeed color- Y- yellow y- green

10.4 How Are Multiple Traits 10.4 How Are Multiple Traits Inherited?Inherited?

Mendel concluded the origination of single traits Mendel concluded the origination of single traits inheritanceinheritance

He then pursued more complex questions relative to He then pursued more complex questions relative to the inheritance of multiple traitsthe inheritance of multiple traits

Initial experiments included crossbreeding plants Initial experiments included crossbreeding plants that differed in two traitsthat differed in two traits• Seed color (yellow or green)Seed color (yellow or green)

• Seed shape (smooth or wrinkled)Seed shape (smooth or wrinkled)

Figure 10-10 Traits of pea plants studied by Gregor MendelFigure 10-10 Traits of pea plants studied by Gregor Mendel

Seedshape

Seedcolor

Podshape

Podcolor

Plantsize

Flowercolor

Flowerlocation

Trait Dominant form Recessive form

smooth wrinkled

yellow green

yellowgreen

inflated constricted

whitepurple

at tips ofbranches

at leafjunctions

dwarf(about 8 to16 inches)

tall(about6 feet)


From the many pea plant phenotypes, he chose From the many pea plant phenotypes, he chose seed color (yellow vs. green peas) and seed shape seed color (yellow vs. green peas) and seed shape (smooth vs. wrinkled peas)(smooth vs. wrinkled peas)• Yellow color is dominant to green colorYellow color is dominant to green color• Smooth shape is dominant to wrinkledSmooth shape is dominant to wrinkled

The allele symbols were assigned, as follows:The allele symbols were assigned, as follows:• YY = yellow (dominant), = yellow (dominant), yy = green (recessive) = green (recessive)• SS = smooth (dominant), = smooth (dominant), ss = wrinkled (recessive) = wrinkled (recessive)


The two-trait cross was between two true-breeding The two-trait cross was between two true-breeding varieties for each characteristic, one dominant for varieties for each characteristic, one dominant for both traits, the other recessive for both traitsboth traits, the other recessive for both traits• P: P: SSYYSSYY (smooth, yellow) (smooth, yellow) ssyyssyy (wrinkled, green) (wrinkled, green)

• The The SSYYSSYY plant produced only plant produced only SYSY gametes, and the gametes, and the ssyyssyy plant produced only plant produced only sysy gametes gametes

• Therefore, the FTherefore, the F11 consisted solely of consisted solely of SsYySsYy individuals, individuals,

with smooth skins and yellow coloringwith smooth skins and yellow coloring


Mendel next allowed the FMendel next allowed the F11 individuals to self- individuals to self-fertilize: fertilize: SsYySsYy SsYySsYy

Crossing the FCrossing the F11 plants yielded 315 plants with plants yielded 315 plants with smooth, yellow seeds; 101 with wrinkled, yellow smooth, yellow seeds; 101 with wrinkled, yellow seeds; 108 with smooth, green seeds; and 32 with seeds; 108 with smooth, green seeds; and 32 with wrinkled, green seedswrinkled, green seeds• This is a ratio of approximately 9:3:3:1This is a ratio of approximately 9:3:3:1

Two-trait crosses of other traits produced similar Two-trait crosses of other traits produced similar proportions of phenotype combinations proportions of phenotype combinations

Figure 10-11 Predicting genotypes and phenotypes for a cross between parents that are heterozygous for two traitsFigure 10-11 Predicting genotypes and phenotypes for a cross between parents that are heterozygous for two traits

sY

self-fertilize

eggs

sySy

Ss Yy

seed shape seed color phenotypic ratio(9:3:3:1)

Using probabilities to determine the offspringof a two-trait cross

wrinkled green

wrinkled yellow

smooth yellow

wrinkled green

smooth green

wrinkled yellow

smooth yellow

smooth green

SY

sY

sy

Sy

SY

SsYY SsYySSYySSYY

SsyY SsyySSyySSyY

ssYY ssYysSYysSYY

ssyY ssyysSyysSyY

Punnett square of a two-trait cross

sp

erm


Mendel hypothesized that traits are inherited Mendel hypothesized that traits are inherited independentlyindependently Mendel predicted that if the two traits were Mendel predicted that if the two traits were

inherited independently, then for each trait, three-inherited independently, then for each trait, three-quarters of the offspring should show the quarters of the offspring should show the dominant phenotype and one-quarter should dominant phenotype and one-quarter should show the recessive phenotype show the recessive phenotype • a 3:1 ratio, as he had found for the single trait flower a 3:1 ratio, as he had found for the single trait flower

colorcolor


Mendel hypothesized that traits are inherited Mendel hypothesized that traits are inherited independently independently (continued)(continued) He found 423 plants with smooth seeds He found 423 plants with smooth seeds

(of either color) and 133 with wrinkled seeds (of either color) and 133 with wrinkled seeds (a ratio of about 3:1)(a ratio of about 3:1)

He found 416 plants produced yellow seeds He found 416 plants produced yellow seeds (of either shape) and 140 produced green seeds (of either shape) and 140 produced green seeds (also about 3:1)(also about 3:1)


Mendel hypothesized that traits are inherited Mendel hypothesized that traits are inherited independently independently (continued)(continued) The independent inheritance of two or more traits The independent inheritance of two or more traits

is called the is called the law of independent assortmentlaw of independent assortment Multiple traits are inherited independently Multiple traits are inherited independently

because the alleles of one gene are distributed to because the alleles of one gene are distributed to gametes independently of the alleles for other gametes independently of the alleles for other genesgenes

Independent assortment will occur when the traits Independent assortment will occur when the traits being studied are controlled by genes on different being studied are controlled by genes on different pairs of homologous chromosomespairs of homologous chromosomes


Mendel hypothesized that traits are inherited Mendel hypothesized that traits are inherited independently independently (continued)(continued) The physical basis of independent assortment The physical basis of independent assortment

has to do with the way homologous pairs line up has to do with the way homologous pairs line up during meiosisduring meiosis

Which of the two homologues is “on top” occurs Which of the two homologues is “on top” occurs randomly for all pairs, so the homologues assort randomly for all pairs, so the homologues assort randomly and independently of one another at randomly and independently of one another at anaphase Ianaphase I

Animation: The Inheritance of Multiple Traits

Figure 10-12 Independent assortment of allelesFigure 10-12 Independent assortment of alleles

Y

S

independent assortment produces four equallylikely allele combinations during meiosis

pairs of alleles on homologouschromosomes in diploid cells

replicated homologouspair during metaphase of

meiosis I, orientinglike this

or like this

chromosomes replicate

meiosis I

meiosis II

y

s

Y

S y

s

YS y s

YS y s

YS

ys

Y

S

y

s

YS ys

YS ys

Y

S

y

s

y

s

Y

S S

y Y

s

Sy sYSY sy

10.4 How Are Multiple Traits 10.4 How Are Multiple Traits Inherited?.Inherited?.

In an unprepared world, genius may go In an unprepared world, genius may go unrecognizedunrecognized Mendel’s work was published in 1865 but went Mendel’s work was published in 1865 but went

unnoticedunnoticed Three biologists—Carl Correns, Hugo de Vries, Three biologists—Carl Correns, Hugo de Vries,

and Erich Tschermak—independently (of Mendel and Erich Tschermak—independently (of Mendel and each other) rediscovered Mendel’s principles and each other) rediscovered Mendel’s principles of inheritance in 1900of inheritance in 1900

Mendel was credited in new papers as laying the Mendel was credited in new papers as laying the groundwork of genetics 30 years previouslygroundwork of genetics 30 years previously

10.5 Do the Mendelian Rules of 10.5 Do the Mendelian Rules of Inheritance Apply to All Inheritance Apply to All

Traits?Traits? Each trait is completely controlled by a single geneEach trait is completely controlled by a single gene Only two possible alleles of each gene existOnly two possible alleles of each gene exist One allele is completely dominant to the other, One allele is completely dominant to the other,

recessive, allelerecessive, allele Most traits are influenced in more varied and subtle Most traits are influenced in more varied and subtle

waysways

Dihybrid crossDihybrid cross

Parent- round and yellowParent- round and yellow

RrYyRrYy

Dihybrid CrossDihybrid Cross

Fill in all the genotypes for the previous Fill in all the genotypes for the previous slide.slide.

mendel’s genetics. where did that blonde hair come from? law of segregation and random assortment...

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