Mendel - Genetic

7/18/2019 Mendel - Genetic

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Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures forBiology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 14

Mendel and the Gene Idea


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Overview: Drawing from the Deck of Genes

What genetic principles account for the

transmission of traits from parents to offspring?


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One possible explanation of hereit! is a

"blening# h!pothesis $he iea that genetic material contribute b!

two parents mixes in a manner analogous to

the wa! blue an !ellow paints blen to makegreen


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%n alternative to the blening moel is the

"particulate# h!pothesis of inheritance: thegene iea

Parents pass on iscrete heritable units& genes


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Gregor 'enel

Documente a particulate mechanism ofinheritance through his experiments with

garen peas

Figure 14.1


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(oncept )*+): 'enel use the scientific

approach to ientif! two laws of inheritance 'enel iscovere the basic principles of

hereit!

,! breeing garen peas in carefull! planne

experiments


7/79Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Mendels Experimental, Quantitative Approach

'enel chose to work with peas

,ecause the! are available in man! varieties

,ecause he coul strictl! control which plants

mate with which



(rossing pea plants

Figure 14.2

)

-

*

.

/

0emove stamens

from purple flower

$ransferre sperm1

bearing pollen from

stamens of white

flower to egg1

bearing carpel of

purple flower

Parental

generation(P)

Pollinate carpel

mature into po

(arpel

2female3

4tamens

2male3

Plante sees

from po

5xamine

offspring:

all purple

flowers

First

generation

offspring

(F1)

APPLICATION ,! crossing 2mating3 two true1breeingvarieties of an organism& scientists can stu! patterns of

inheritance+ 6n this example& 'enel crosse pea plants

that varie in flower color+

TECNI!"ETECNI!"E

When pollen from a white f lower fertili7es

eggs of a purple flower& the first1generation h!bris all have purple

flowers+ $he result is the same for the reciprocal cross& the transfer

of pollen from purple flowers to white flowers+

TECNI!"E#E$"LT$



4ome genetic vocabular!

(haracter: a heritable feature& such as flowercolor

$rait: a variant of a character& such as purple

or white flowers



'enel chose to track

Onl! those characters that varie in an "either1or# manner

'enel also mae sure that

8e starte his experiments with varieties that

were "true1breeing#



6n a t!pical breeing experiment

'enel mate two contrasting& true1breeingvarieties& a process calle h!brii7ation

$he true1breeing parents

%re calle the P generation



$he h!bri offspring of the P generation

%re calle the 9)generation

When 9)iniviuals self1pollinate

$he 9/generation is prouce



he La! o" #e$re$ation

When 'enel crosse contrasting& true1

breeing white an purple flowere pea plants %ll of the offspring were purple

When 'enel crosse the 9)plants

'an! of the plants ha purple flowers& but

some ha white flowers



'enel iscovere

% ratio of about three to one& purple to white flowers&in the 9/generation

Figure 14.%

P &eneration

2true1breeing

parents3 Purpleflowers

Whiteflowers

F1 &eneration

2h!bris3

%ll plants ha

purple flowers

F2 &eneration

E'PE#IENT $rue1breeing purple1flowere pea plants an

white1flowere pea plants were crosse 2s!mboli7e b! 3+ $he

resulting 9)h!bris were allowe to self1pollinate or were cross1

pollinate with other 9)h!bris+ 9lower color was then observe

in the 9/

generation+

#E$"LT$ ,oth purple1flowere plants an white1

flowere plants appeare in the 9/generation+ 6n 'enels

experiment& ;


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'enel reasone that

6n the 9)plants& onl! the purple flower factorwas affecting flower color in these h!bris

Purple flower color was ominant& an white

flower color was recessive


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'enel observe the same pattern

6n man! other pea plant characters

Tale 14.1


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Mendels Model

'enel evelope a h!pothesis

$o explain the .:) inheritance pattern that heobserve among the 9/offspring

9our relate concepts make up this moel


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9irst& alternative versions of genes

%ccount for variations in inherite characters&which are now calle alleles

Figure 14.4

Allele for purple flo*ers

Lo+us for flo*er,+olor gene

o-ologous

pair of

+hro-oso-es

Allele for *hite flo*ers


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4econ& for each character

%n organism inherits two alleles& one fromeach parent

% genetic locus is actuall! represente twice


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$hir& if the two alleles at a locus iffer

$hen one& the ominant allele& etermines theorganisms appearance

$he other allele& the recessive allele& has no

noticeable effect on the organismsappearance


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9ourth& the law of segregation

$he two alleles for a heritable characterseparate 2segregate3 uring gamete formation

an en up in ifferent gametes


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Does 'enels segregation moel account for

the .:) ratio he observe in the 9/

generationof his numerous crosses?

We can answer this =uestion using a Punnett

s=uare


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'enels law of segregation& probabilit! an

the Punnett s=uare

Figure 14.

P &eneration

F1&eneration

F2&eneration

P p

P p

P p

P

p

PpPP

ppPp

%ppearance:

Genetic makeup:Purple flowers

PP

White flowers

pp

Purple flowers

Pp

%ppearance:

Genetic makeup:

Gametes:

Gametes:

9)sperm

9)eggs

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5ach true1breeing plant of the

parental generation has ientical

alleles& PPorpp+

Gametes 2circles3 each contain onl!

one allele for the flower1color gene+

6n this case& ever! gamete prouce

b! one parent has the same allele+

nion of the parental gametesprouces 9)h!bris having a Pp

combination+ ,ecause the purple1

flower allele is ominant& all

these h!bris have purple flowers+

When the h!bri plants prouce

gametes& the two alleles segregate&

half the gametes receiving the P

allele an the other half thepallele+

. : )

0anom combination of the gametes

results in the .:) ratio that 'enel

observe in the 9/generation+

$his box& a Punnett s=uare& shows

all possible combinations of allelesin offspring that result from an

9)9)2PpPp3 cross+ 5ach s=uare

represents an e=uall! probable prouctof fertili7ation+ 9or example& the bottom

left box shows the genetic combination

resulting from a p egg fertili7e b!

a P sperm+


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Useful Genetic Vocabulary

%n organism that is homo7!gous for a

particular gene 8as a pair of ientical alleles for that gene

5xhibits true1breeing

%n organism that is hetero7!gous for a

particular gene

8as a pair of alleles that are ifferent for thatgene


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%n organisms phenot!pe

6s its ph!sical appearance

%n organisms genot!pe

6s its genetic makeup


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Phenot!pe versus genot!pe

Figure 14.0

%

1 1

2

1

Phenotpe

Purple

Purple

Purple

White

&enotpe

PP

2homo7!gous3

Pp

2hetero7!gous3

Pp

2hetero7!gous3

pp

2homo7!gous3

0atio .:) 0atio ):/:)


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The Testcross

6n pea plants with purple flowers

$he genot!pe is not immeiatel! obvious


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% testcross

%llows us to etermine the genot!pe of anorganism with the ominant phenot!pe& but

unknown genot!pe

(rosses an iniviual with the ominantphenot!pe with an iniviual that is

homo7!gous recessive for a trait


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$he testcross

Figure 14.

Dominant phenot!pe&

unknown genot!pe:

PP or Pp?

0ecessive phenot!pe&

known genot!pe:

pp

6f PP&

then all offspring

purple:

6f Pp&

then )@/offspring purple

an )@/offspring white:

p p

P

P

Pp Pp

PpPp

pp pp

PpPpP

p

p p

APPLICATION %n organism that exhibits a ominant trait&such as purple flowers in pea plants& can be either homo7!gous for

the ominant allele or hetero7!gous+ $o etermine the organisms

genot!pe& geneticists can perform a testcross+

TECNI!"E 6n a testcross& the iniviual with the

unknown genot!pe is crosse with a homo7!gous iniviual

expressing the recessive trait 2white flowers in this example3+

,! observing the phenot!pes of the offspring resulting from thiscross& we can euce the genot!pe of the purple1flowere

parent+

#E$"LT$


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he La! o" Independent Assortment

'enel erive the law of segregation

,! following a single trait

$he 9)offspring prouce in this cross

Were monoh!bris& hetero7!gous for onecharacter


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'enel ientifie his secon law of inheritance

,! following two characters at the same time

(rossing two& true1breeing parents iffering in

two characters

Prouces ih!bris in the 9)generation&

hetero7!gous for both characters


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8ow are two characters transmitte from

parents to offspring?

%s a package?

6nepenentl!?


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YYRRP &eneration

Gametes YR yr

yyrr

YyRr8!pothesis of

epenent

assortment

8!pothesis of

inepenent

assortment

F2&eneration

2preicte

offspring3

)@/ YR

YR

yr

)@/

)@/

)@/ yr

YYRR YyRr

yyrrYyRr

.@* )@*

4perm

5ggs

Phenot!pic ratio .:)

YR)@*

Yr)@*

yR)@*

yr)@*

A@)B.@)B

.@)B)@)B

YYRRYYRr YyRRYyRr

YyrrYyRrYYrrYYrr

YyRR YyRr yyRR yyRr

yyrryyRrYyrrYyRr

Phenot!pic ratio A:.:.:)

.)- )


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sing the information from a ih!bri cross&

'enel evelope the law of inepenent

assortment

5ach pair of alleles segregates inepenentl!

uring gamete formation


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(oncept )*+/: $he laws of probabilit! govern

'enelian inheritance

'enels laws of segregation an inepenent

assortment

0eflect the rules of probabilit!

h M lti li ti d Additi R l A li d t


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he Multiplication and Addition Rules Applied toMonohybrid Crosses

$he multiplication rule 4tates that the probabilit! that two or more

inepenent events will occur together is the

prouct of their iniviual probabilities


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Probabilit! in a monoh!bri cross

(an be etermine using this rule

Rr

4egregation of

alleles into eggs

Rr

4egregation of

alleles into sperm

R r

rR

RR

R)@/

)@/)@/

)@*)@*

)@*)@*

)@/ r

rR r

r

4perm

5ggs

Figure 14.


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$he rule of aition

4tates that the probabilit! that an! one of twoor more exclusive events will occur is

calculate b! aing together their iniviual

probabilities

# l i C l G ti % bl ith th R l


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#olvin$ Complex Genetics %roblems !ith the Ruleso" %robability

We can appl! the rules of probabilit! $o preict the outcome of crosses involving

multiple characters


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% ih!bri or other multicharacter cross

6s e=uivalent to two or more inepenentmonoh!bri crosses occurring simultaneousl!

6n calculating the chances for various

genot!pes from such crosses

5ach character first is consiere separatel!

an then the iniviual probabilities are

multiplie together


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(oncept )*+.: 6nheritance patterns are often

more complex than preicte b! simple

'enelian genetics

$he relationship between genot!pe an

phenot!pe is rarel! simple

Extendin$ Mendelian Genetics "or a #in$le Gene


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Extendin$ Mendelian Genetics "or a #in$le Gene

$he inheritance of characters b! a single gene

'a! eviate from simple 'enelian patterns

The Spectrum of Dominance


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The Spectrum of Dominance

(omplete ominance

Occurs when the phenot!pes of thehetero7!gote an ominant homo7!gote are

ientical


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6n coominance

$wo ominant alleles affect the phenot!pe inseparate& istinguishable wa!s

$he human bloo group 'E

6s an example of coominance


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6n incomplete ominance

$he phenot!pe of 9)h!bris is somewhere betweenthe phenot!pes of the two parental varieties

Figure 14.15

P Generation

9)Generation

9/Generation

0e

CRCR

Gametes CR CW

White

CWCW

Pink

CRCW

4perm

CR

CR

CR

Cw

CR

CRGametes

162 162

162

162

162

5ggs162

CR CR CR CW

CW CWCR CW


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$he 0elation ,etween Dominance an

Phenot!pe

Dominant an recessive alleles

Do not reall! "interact#

Lea to s!nthesis of ifferent proteins that

prouce a phenot!pe


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9re=uenc! of Dominant %lleles

Dominant alleles

%re not necessaril! more common in

populations than recessive alleles

Multiple lleles


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Multiple lleles

'ost genes exist in populations

6n more than two allelic forms


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$he %,O bloo group in humans

6s etermine b! multiple alleles

Tale 14.2

!leiotropy


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!leiotropy

6n pleiotrop!

% gene has multiple phenot!pic effects

Extendin$ Mendelian Genetics "or !o or More Genes


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Extendin$ Mendelian Genetics "or !o or More Genes

4ome traits

'a! be etermine b! two or more genes

"pistasis


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"pistasis

6n epistasis

% gene at one locus alters the phenot!picexpression of a gene at a secon locus


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%n example of epistasis

Figure 14.11

BC bC Bc bc)@*)@*

)@*)@*

BC

bC

Bc

bc

)@*

)@*

)@*

)@*

BBCc BbCc BBcc Bbcc

Bbcc bbccbbCcBbCc

BbCC bbCC BbCc bbCc

BBCC BbCC BBCc BbCc

A@)B.@)B

*@)B

BbCc BbCc

$per-

Eggs

!oly#enic $nheritance


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!oly#enic $nheritance

'an! human characters

Far! in the population along a continuum anare calle =uantitative characters


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AaBbCc AaBbCc

aabbccAabbccAaBbcc AaBbCc AABbCcAABBCcAABBCC

/


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&ature and &urture' he Environmental Impacton %henotype

%nother eparture from simple 'eneliangenetics arises

When the phenot!pe for a character epens

on environment as well as on genot!pe


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$he norm of reaction

6s the phenot!pic range of a particulargenot!pe that is influence b! the environment

Figure 14.1%


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'ultifactorial characters

%re those that are influence b! both genetican environmental factors

Inte$ratin$ a Mendelian (ie! o" )eredity and (ariation


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$ $ y

%n organisms phenot!pe

6nclues its ph!sical appearance& internalanatom!& ph!siolog!& an behavior

0eflects its overall genot!pe an uni=ue

environmental histor!


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5ven in more complex inheritance patterns

'enels funamental laws of segregation aninepenent assortment still appl!


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(oncept )*+*: 'an! human traits follow

'enelian patterns of inheritance

8umans are not convenient subHects for

genetic research

8owever& the stu! of human geneticscontinues to avance

%edi$ree Analysis


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$ y

% peigree

6s a famil! tree that escribes theinterrelationships of parents an chilren

across generations


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6nheritance patterns of particular traits

(an be trace an escribe using peigrees

Figure 14.14 A7 8

Ww ww ww Ww

wwWwWwwwwwWw

WW

or

Ww

ww

9irst generation

2granparents3

4econ generation

2parents plus aunts

an uncles3

$hir

generation

2two sisters3

Ff Ff ff Ff

ffFfFfffFfFF or Ff

ff FF

or

Ff

Wiows peak Eo Wiows peak %ttache earlobe 9ree earlobe

(a) 9o-inant trait (*i:o*;s pea


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Peigrees

(an also be use to make preictions aboutfuture offspring

Recessively Inherited *isorders


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y

'an! genetic isorers

%re inherite in a recessive manner


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0ecessivel! inherite isorers

4how up onl! in iniviuals homo7!gous forthe allele

(arriers

%re hetero7!gous iniviuals who carr! the

recessive allele but are phenot!picall! normal

Cystic %ibrosis


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y

4!mptoms of c!stic fibrosis inclue

'ucus builup in the some internal organs

%bnormal absorption of nutrients in the small

intestine

Sic&le'Cell Disease


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4ickle1cell isease

%ffects one out of *


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# f

'atings between relatives

(an increase the probabilit! of the appearanceof a genetic isease

%re calle consanguineous matings

*ominantly Inherited *isorders


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y

4ome human isorers

%re ue to ominant alleles


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One example is achonroplasia

% form of warfism that is lethal whenhomo7!gous for the ominant allele

Figure 14.1


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8untingtons isease

6s a egenerative isease of the nervouss!stem

8as no obvious phenot!pic effects until about

.- to *< !ears of age

Figure 14.10

Multi"actorial *isorders


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'an! human iseases

8ave both genetic an environmentcomponents

5xamples inclue

8eart isease an cancer

Genetic estin$ and Counselin$


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Genetic counselors

(an provie information to prospective parentsconcerne about a famil! histor! for a specific

isease

Counselin# )ased on Mendelian Genetics and


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!robability Rules

sing famil! histories

Genetic counselors help couples etermine the

os that their chilren will have genetic

isorers

Tests for $dentifyin# Carriers


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9or a growing number of iseases

$ests are available that ientif! carriers anhelp efine the os more accuratel!

%etal Testin#


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6n amniocentesis

$he li=ui that bathes the fetus is remove anteste

6n chorionic villus sampling 2(F43

% sample of the placenta is remove an

teste


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9etal testing

Figure 14.1 A7 8

(a) A-nio+entesis

%mniotic

fluiwithrawn

9etus

Placenta terus (ervix

(entrifugation

% sample of

amniotic flui canbe taken starting at

the )*th to )Bthweek of pregnanc!+

() Chorioni+ =illus sa-pling (C>$)

9lui

9etal

cells

,iochemical tests can bePerforme immeiatel! on

the amniotic flui or later

on the culture cells+

9etal cells must be culture

for several weeks to obtainsufficient numbers for

kar!ot!ping+

4everal

weeks

8io+he-i+al

tests

4everalhours

9etalcells

Placenta (horionic vi66i

% sample of chorionic villus

tissue can be taken as earl!as the Cth to )


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4ome genetic isorers can be etecte at

birth

,! simple tests that are now routinel!

performe in most hospitals in the nite

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