S A N C L E M E N T E H I G H S C H O O L.docx

8/22/2019 S A N C L E M E N T E H I G H S C H O O L.docx

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S A N C L E M E N T E H I G H S C H O O L

Punnett Squares

Punnett Squares Made Easy!Download "cheat sheet"

Below is a sampling of Punnett Square problems that you will be

expected to solve. In order to do this, you will have to understand themeaning of the terms below.

Genotype: The letters that make up the individual. E.g. TT or TtPhenotype: The physical characteristics of the particular trait. E.g. Tall orshor tDominant trait: Signified by capital letter-E.g. T. If the traits you are using aredominant or recessive, this trait will "overpower" the recessive trait and will beexpressed. E.g. TtRecessive trait: Signified by small case letter-e.g. t. An organism with arecessive allele for a particular form of a trait will have that form only when thedominant allele for the trait is not presentHomozygous: Has same letters. E.g. TTort t (same alleles for trait)Heterozygous: Has different letters. E.g. Tt (different alleles for trait)Purebred trait: Also known as true breeding. Individuals genotype is

homozygous and will only make one type of gamete. E.g TT will alwaysproduces T, and T. tt will always produce t, and t.

Gamete: sex cells. Represented by letter N (meaning they are haploid-contain half the chromosomesP generation: The parental generation (Usually the first one in a genetic cross)
http://docushare.capousd.org/docushare/dsweb/Get/Document-3933/PUNNETT+SQUARE+CHEAT+SHEET.pdfhttp://docushare.capousd.org/docushare/dsweb/Get/Document-3933/PUNNETT+SQUARE+CHEAT+SHEET.pdfhttp://sctritons.schoolloop.com/http://sctritonscience.com/Wilson/fun_stuff.htmhttp://sctritonscience.com/Wilson/summer%20school.htmhttp://sctritonscience.com/Wilson/biology.htmhttp://sctritonscience.com/Wilson/physics.htmhttp://sctritonscience.com/Wilson/indexwilson.htmhttp://sctritons.schoolloop.com/http://sctritonscience.com/Wilson/fun_stuff.htmhttp://sctritonscience.com/Wilson/summer%20school.htmhttp://sctritonscience.com/Wilson/biology.htmhttp://sctritonscience.com/Wilson/physics.htmhttp://sctritonscience.com/Wilson/indexwilson.htmhttp://sctritons.schoolloop.com/http://sctritonscience.com/Wilson/fun_stuff.htmhttp://sctritonscience.com/Wilson/summer%20school.htmhttp://sctritonscience.com/Wilson/biology.htmhttp://sctritonscience.com/Wilson/physics.htmhttp://sctritonscience.com/Wilson/indexwilson.htmhttp://sctritons.schoolloop.com/http://sctritonscience.com/Wilson/fun_stuff.htmhttp://sctritonscience.com/Wilson/summer%20school.htmhttp://sctritonscience.com/Wilson/biology.htmhttp://sctritonscience.com/Wilson/physics.htmhttp://sctritonscience.com/Wilson/indexwilson.htmhttp://sctritons.schoolloop.com/http://sctritonscience.com/Wilson/fun_stuff.htmhttp://sctritonscience.com/Wilson/summer%20school.htmhttp://sctritonscience.com/Wilson/biology.htmhttp://sctritonscience.com/Wilson/physics.htmhttp://sctritonscience.com/Wilson/indexwilson.htmhttp://sctritons.schoolloop.com/http://sctritonscience.com/Wilson/fun_stuff.htmhttp://sctritonscience.com/Wilson/summer%20school.htmhttp://sctritonscience.com/Wilson/biology.htmhttp://sctritonscience.com/Wilson/physics.htmhttp://sctritonscience.com/Wilson/indexwilson.htmhttp://docushare.capousd.org/docushare/dsweb/Get/Document-3933/PUNNETT+SQUARE+CHEAT+SHEET.pdf


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F1 generation: The f i rs tgeneration of offspring from P generation (means firstfilial: Latin for "son")F2 generation: The secondgeneration of offspring from P generation (meansfirst filial: Latin for "son")Monohybrid Cross: Also known as a Single-Factor Cross. Only one trait isused in the genetic cross. E.g. T=Tall, t=short. Example: Tt x TtDihybrid Cross: Also known as a Two-factor Cross. Two trait are used in thegenetic cross. E.g. T=Tall, t=short & B=Black fur, b=white fur. Example TtBbx TTBBIncomplete Dominance: One allele is not completely dominant over theother. There is a blending with the heterozygous offspring. E.g. RR=Red,Rr=Pink, and rr=whiteCo-dominance: Both alleles contribute to the phenotype. Offspring will havecombination of two alleles. E.g. RR=Red hair, Rr=Roan (mix of red and whitehairs-almost looks pink), and rr=whiteSex-linked trait: Genes located on the sex-chromosomes called sex-l inkedgenes. Usually found on the X chromosome. X-linked alleles are alwaysexpressed in males because males have only one X chromosome.Multiple Alleles: There are more than two-choices for the allele. Example is

human blood group genes. There are three possible alleles for this gene. I

A

, I

B

,and i. IA and IBare co-dominant. There are four possible phenotypes: A, B,

AB, and O.

Genotypic ratios: The ratio of different genotype in the offspring from a geneticcross. E.g 1:2:1Phenotypic ratios: The ratio of different phenotypes in the offspring from agenetic cross. E.g 3:1

Sample Problems


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Monohybrid(Dominant andRecessive)PROBLEM: Cro

ss twoheterozygousTall peaplants. Givegenotypic andphenotypicratios.STEP1: Determinewhat kind of

problem you aretrying to solve.

Does itinvolvesimpledominantandrecessivetraits, Incomplete

dominance, or Co-dominance?

Is it amonohybrid ordihyrid?

In thiscase thereis only one

trait..........this isa monohybr id cross

involv ing

dominant

an d

recessive


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trai ts.STEP2: Determineletters you will

use to specifytraits.

In thiscase it isdominantandrecessive,so you canuse Tandt.

STEP3: Determineparentsgenotypes.

In thiscase youwere toldtheparents

wereheterozygous. Youthereforeknow thattheparentsmustbe TtandTt

The Cross

is: Tt X Tt

STEP 4: Makeyour punnetsquare and makegametes (thesego on the top andside of your


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punnett square. Ttwould

makea Tand a t

STEP5: Completecross anddeterminepossibleoffspring.STEP6: Determinegenotypic and

phenotypic ratios. Genotypic

ratio: Make a list ofall thedifferentgenotypes(the lettercombinations) and

determinehow manyof eachyou have.

o Inyourproblemthis

wouldbe:TT

=

1,

Tt =

2, a


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nd tt -

1.Thegen

otypicratiowouldthereforebe1 :

2 :1

Phenotypicratio: Make a list ofall thedifferentphenotypes (physicalcharacteris

tics.o In

youproblemthiswouldbe:Ta l

l =3,

and

sho

rt =

1.Thephe


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notypicratiowou

ldthereforebe3 :

1


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Monohybrid(IncompleteDominance)PROBLEM: Cr

oss twoheterozygousplants. Givegenotypic andphenotypicratios. The tallgene is thisplant isincompletelydominant overthe short

gene. TT=Tall,Tt=medium,and tt=short.STEP1: Determinewhat kind ofproblem youare trying tosolve.

Does itinvolvesimpledominantandrecessivetraits, Incompletedominance, or

Co-dominance?


In this


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casethere isonly onetrait..........this is

a monohybr id

cross

involv in

g

incompl

et e

domina

nt trai ts .STEP

2: Determineletters you willuse to specifytraits.

In thiscase it isaincompletedominant

problem. TT=tall,Tt=medi

um , and

tt=shortSTEP3: Determineparentsgenotypes.

In thiscase youwere toldtheparentswereheterozygous. Y


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outhereforeknowthat theparents

mustbe Ttand Tt

TheCrossis: Tt XTt

STEP 4: Makeyour punnetsquare and

make gametes(these go onthe top and sideof your punnettsquare.

Ttwouldmakea Tanda t

STEP5: Completecross anddeterminepossibleoffspring.STEP6: Determinegenotypic andphenotypic

ratios.

Genotypicratio: Make a listof all thedifferent


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genotypes (thelettercombinations) and

determine howmany ofeach youhave.

o Inyourproble

mthiswouldbe:T

T

=

1,

Tt

=

2,

andtt

-

1.

Thegenotypicra


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tiowouldth

ereforebe1:

2

:

1

Phenoty

picratio: Make a listof all thedifferentphenotypes(physicalcharacteristics.

o In

youproblemthiswould

be:T

all

=

1,

m

e


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d i

u

m

=

2,

an

d

s

h

or

t

=

1.

T

hephenotypicratiowould

thereforebe1:

2

:

1


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Monohybrid(Co-dominant)PROBLEM: Cr

oss twoheterozygoustan cows. Givegenotypic andphenotypicratios. BB=Black, BW=tan,and WW=whiteSTEP1: Determine

what kind ofproblem you aretrying to solve.

Does itinvolvesimpledominantandrecessivetraits, Inc

ompletedominance, or Co-dominance?


In thiscase

there isonly onetrait..........this isa monohybr id

cross

involv in


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g co-

dominan

t traits.STEP

2: Determineletters you willuse to specifytraits.

In thiscase it isaincompletedominant

problem.TT=tall,

Tt=medi

um , and

tt=shortSTEP3: Determineparentsgenotypes.

In thiscase youwere toldtheparentswereheterozygous. Youthereforeknow that

theparentsmustbe BWand BW

TheCrossis: BW x


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BWSTEP 4: Makeyour punnetsquare and

make gametes(these go on thetop and side ofyour punnettsquare.

BWwould makea Banda Wforboth

parentsSTEP5: Completecross anddeterminepossibleoffspring.STEP6: Determine

genotypic andphenotypicratios.

Genotypicratio: Make a listof all thedifferentgenotype

s (thelettercombinations) anddetermine howmany ofeach you


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have.o In

yourpr

oblemthiswouldbe:B

B

=1,

B

W

=

2,

andW

W

=1.

Thegenotypicratio

wouldthereforebe


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1: 2

:

1

Phenoty

picratio: Make a listof all thedifferentphenotypes(physicalcharacteristics.

o In

youproblemthiswouldbe

:B lac

k

=

1,

Ta

n

=

2,

an

dW

hit

e

=

1.

Th


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ephenotypic

ratiowouldthereforebe1

: 2: 1


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Monohybrid(sex-linked)PROBLEM: Crossa female carrier for

hemophilia with amale withhemophilia. H=normal, andh=hemophiliaSTEP 1: Determinewhat kind ofproblem you aretrying to solve.

Does itinvolvesimpledominant andrecessivetraits, Incompletedominance,or Co-dominance?

Is it a

monohybridor dihyrid?

In this casethere is onlyonetrait..........thisisa monohybr id cross

involv ing

sex l inked

traits.STEP 2: Determineletters you will useto specify traits.

In this case itis a sex-


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linkedproblem. Rememberthat XXisfemale,

and XYismale. H=normal andh=hemophilia. Normallyyou wouldnot write thecapital letterson thegenotypes,only the

small case(therecessivegeneresponsiblefor thedisorder)

STEP 3: Determineparents genotypes.

In this caseyou were toldthe parentswere: Female carr ier =

XhX, and

a male withhemophi l ia

= XhY.

The Crossis: XhXx Xh

Y

STEP 4: Make yourpunnet square andmake gametes(these go on the topand side of your


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punnett square. X

hXwould

makea Xhand X

Xh

Ywouldmakea Xhand Y

NOTE: Thefemalesgametesalways go ontop of thepunnettsquare andthe males on

the side.

STEP 5: Completecross and determinepossible offspring.STEP 6: Determinegenotypic andphenotypic ratios.

Genotypic

ratio: Makea list of allthe differentgenotypes(the lettercombinations) anddeterminehow many ofeach youhave.

o

In yourproblem thiswouldbe: Xh

X =

1, Xh

Xh=


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1, andXY= 1,

and XhY =

1The

genotypicratiowouldthereforebe 1 :1 : 1 :

1

Phenotypicratio: Make

a list of allthe differentphenotypes(physicalcharacteristics.

o In youproblem thiswouldbe: F

emaleCarrier= 1,Female w/hemophilia =1,Normal male= 1,

andMalew/hemophilia =1.

The


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phenotypicratiowouldbe 1 :

1 : 1 :1


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Monohybrid(Multiple Alleles)PROBLEM: Cross aperson with type AB

blood with a personwho is heterozygousfor type A blood.STEP 1: Determinewhat kind of problemyou are trying tosolve.

Does it involvesimple dominant

and recessivetraits, Incomplete dominance,or Co-dominance, ormultiple alleles?


In this casethere is only

onetrait..........this isa monohybr idcross

involv ing mul t i

ple allelesSTEP 2: Determineletters you will use tospecify traits.

There are morethan two-choices for theallele. Exampleis human bloodgroupgenes. Thereare three


26/39

possible allelesfor thisgene. IA , IB,an d

i. IA and IBare

co-dominant . There are fourpossiblephenotypes: A,B, AB, and O.

STEP 3: Determineparents genotypes.

In this case you

were told onehas type ABblood

= IAIB. The

otherisheterozygousfor type A = I

Ai

STEP 4: Make yourpunnet square andmake gametes (these

go on the top and sideof your punnett square. I

AIBwould make

a IA and IB I

Aiwould make

a IAand i

STEP 5: Completecross and determinepossible offspring.STEP 6: Determinegenotypic andphenotypic ratios.

Genotypicratio: Make alist of all the


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differentgenotypes (thelettercombinations)and determine

how many ofeach you have.

o In yourproblemthiswouldbe: IA IA =1, I

AIB=

1, and IA i

= 1,

andIBi

= 1 Thegenotypicratiowouldthereforebe 1 : 1 :1 : 1

Phenotypicratio: Make alist of all the

differentphenotypes(physicalcharacteristics.

o In youproblemthiswouldbe: TypeA = 2,

Type AB

= 1, andType B =

1

o Therefore thephenotypic ratiois: 2 : 1


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: 1

Dihybrid

(Dominant andRecessive)PROBLEM: Cross twoheterozygousTall Blackcows. Tall isdominant overshort, and Blackis dominant over

white. Givegenotypic andphenotypic ratiosof offspring.STEP1: Determinewhat kind ofproblem you aretrying to solve.

Does itinvolvesimpledominantandrecessivetraits, Incompletedominance,or Co-dominance

? Is it a

monohybridor dihyrid?

In this casethere aretwotraits.........t


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his isa dihybr idcross

involv ing

dominant

an drecessive

traits.STEP2: Determineletters you will useto specify traits.

In this casethere are

two traitsyou willneed lettersfor. Use T= Tall, and

t = shortforone trait,and B =Black, and

b =

whi tefor

the secondtrait. Theseare bothdominant/recessivegenes

STEP3: Determineparentsgenotypes.

In this caseyou weretold theparentswereheterozygous for both


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traits. Youthereforeknow thatthe parentsmust

be TtBband TtBb

The Crossis: TtBb XTtBb

STEP 4: Makeyour punnetsquare and makegametes (these goon the top and

side of yourpunnett square.

Makinggametes fora dihybridcrossrequiresyouuse FOIL (first-outside-

inside-last)

TtBbwouldmake fourdifferentgametes= TB, Tb,tB, tb

STEP5: Complete crossand determine

possible offspring.

STEP6: Determinegenotypic andphenotypic ratios.

Genotypic


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ratio: Make a list of allthe differentgenotypes(the letter

combinations) anddeterminehow manyof each youhave.

o Thegenotypicratiowoul

dthereforebe 1:2:2:1

:4:1:

2:3:1 Phenotypic

ratio: Make a list of allthe different

phenotypes(physicalcharacteristics.

o Inyouproblemthiswould

be:Tall/Blac

k =

9,

and

Tall/

whi t


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e =

3,

shor

t/Bla

ck =

3,and

shor

t/whi

te =

1.o The

phenotypicratio

wouldthereforebe 9:3:3:1


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Dihybrid(DominantandRecessiveand Sex-linked)PROBLEM: Crossa homozygousTall femalecarrier forhemophilia witha short normalmale. Givegenotypic andphenotypicratios ofoffspring.STEP1: Determinewhat kind ofproblem you aretrying to solve.

Does itinvolvesimpledominantandrecessivetraits, Incompletedominance, or Co-dominance, or sex-linked?


In thiscase


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there aretwotraits.........this isa dihybr i

d crossinvolv ing

dominant

an d

recessive

traits and

sex-

l inked

trait for

hemophi l

ia. STEP2: Determineletters you willuse to specifytraits.

In thiscasethere aretwo traits

you willneedlettersfor. UseT = Tall,

and t =

shor tforone trait,and H=normal ,

and h =

hemophi liafor thesecondsex-linkedtrait. These arebothdominant/


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recessivegenes

STEP3: Determine

parentsgenotypes.

In thiscase youwere toldtheparentswereheterozygous for

bothtraits. Youthereforeknow thattheparentsmustbe XhXTTand XYtt

The Cross

is: Xh

XTTX XYtt

STEP 4: Makeyour punnetsquare andmake gametes(these go on thetop and side ofyour punnettsquare.

Makinggametesfor adihybridcrossrequiresyou


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use FOIL (first-outside-inside-last)

Xh

XTTwould makefourdifferentgametes= XhT,XhT, XT,

and XT XYttwoul

d makefour

differentgametes= Xt, Xt,Yt, and Yt

STEP5: Completecross anddeterminepossibleoffspring. When

you have a sex-linked trait, makesure you put thefemales gameteson top of thepunnett squareand the male'son the side.STEP6: Determine

genotypic andphenotypicratios.

Genotypicratio: Make a list of


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all thedifferentgenotypes(the lettercombinati

ons) anddeterminehow manyof eachyou have.

o Thegenotypic

ratiowouldthereforebe4:4

:4:

4

or1:1

:1:

1 Phenotyp

icratio: Make a list ofall thedifferentphenotyp

es(physicalcharacteristics.

o Inyouproble


38/39

mthiswouldbe:

Tall/

fe

ma

le

car

rier

=

4,

Ta l

l/n

orma

l

fe

ma

le

=

4,

Ta l

l/m

ale

w /he

mo

ph i

l ia

=

4,

an

d

Ta l

l/n

orma

l

ma

le

=

4.o Th


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ephenotypic

ratiowouldthereforebe4:4

:4:

4

or1:1

:1:

1

H E Y ! M R . W I L S O N

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