Punnett SquaresPunnett Squares

Be ready to answer!Be ready to answer!

Which is an example of heterozygous Which is an example of heterozygous alleles?alleles? TtTt MMMM mmmm

Be ready to answer!Be ready to answer!

Which is an example of heterozygous Which is an example of heterozygous alleles?alleles? TtTt MMMM mmmm

ReviewReview

Which is an example of homozygous Which is an example of homozygous dominant alleles?dominant alleles? TtTt MMMM mmmm

ReviewReview

Which is an example of homozygous Which is an example of homozygous dominant alleles?dominant alleles? TtTt MMMM mmmm

ReviewReview

Which is an example of a Which is an example of a purebred?purebred? TtTt MMMM mmmm

ReviewReview

Which is an example of a Which is an example of a purebred?purebred? TtTt MMMM mmmm

ReviewReviewWhich is an example of a Which is an example of a phenotype?phenotype? TtTt tttt Can roll tongueCan roll tongue None of these are examples of None of these are examples of

phenotypesphenotypes

ReviewReviewWhich is an example of a Which is an example of a phenotype?phenotype? TtTt tttt Can roll tongueCan roll tongue None of these are examples of None of these are examples of

phenotypesphenotypes

{{

Probability and Probability and Punnett SquaresPunnett Squares

The likelihood that a specific event The likelihood that a specific event will occurwill occur If you flip a coin 100 times, you should If you flip a coin 100 times, you should

get about 50 heads, 50 tails get about 50 heads, 50 tails

http://www.betweenwaters.com/probab/flip/coinmainD.html

ProbabilityProbability

Fertilization: endless Fertilization: endless possibilities depending possibilities depending on which sperm on which sperm fertilizes the eggfertilizes the egg

Figuring out the Figuring out the probability of specific probability of specific traits can be HARD! traits can be HARD! But one tool makes it But one tool makes it easier…easier…

Probability in GeneticsProbability in Genetics

The value of studying genetics is in The value of studying genetics is in understanding how we can predict the understanding how we can predict the likelihood of inheriting particular traits.  likelihood of inheriting particular traits.  This can help plant and animal breeders in This can help plant and animal breeders in developing varieties that have more developing varieties that have more desirable qualities.  It can also help people desirable qualities.  It can also help people explain and predict patterns of inheritance explain and predict patterns of inheritance in family lines.in family lines.

One of the easiest ways to calculate the One of the easiest ways to calculate the mathematical probability of inheriting a mathematical probability of inheriting a specific trait was invented by an early specific trait was invented by an early 20th century English geneticist named 20th century English geneticist named Reginald PunnettReginald Punnett

Read OnlyRead Only

PUNNETT SQUARESPUNNETT SQUAREScharts showing the possible charts showing the possible combinations of alleles in a combinations of alleles in a crosscrossshow the probability of getting show the probability of getting a certain type of offspringa certain type of offspring

Example with flies:Example with flies:

Monohybrid CrossMonohybrid Cross: a cross that : a cross that involves only one traitinvolves only one trait

Phenotypes: Genotypes:

Each square shows the chance of getting a baby with that genotype

If there are 4 squares, what percent is each square worth?

THE PARENTSTHE PARENTSGENOTYPESGENOTYPESDAD = Tt (heterozygous)DAD = Tt (heterozygous)MOM = Tt (heterozygous)MOM = Tt (heterozygous)

PHENOTYPESPHENOTYPESDAD = TallDAD = TallMOM = TallMOM = Tall

One parent’s genes go across the top(one per box)

The other parent’s genes go down the side (one per box)

Each letter goes into each box below it

Each letter goes into each box next to it

Now we can predict the possibility that the parents will have a baby with that kind of phenotype

What is the possibility (%) that the parents will have a tall baby?

TT = tall 25%Tt = tall50%

So 75% chance

What is the possibility that the parents will have a short baby?

tt = short 25%

So 25% chance

THE OFFSPRINGTHE OFFSPRING

TT (homozygous dominant)TT (homozygous dominant) Tt (heterozygous)Tt (heterozygous) Tt (heterozygous)Tt (heterozygous) tt (homozygous recessive)tt (homozygous recessive)

GENOTYPES1TT:2Tt:1tt (1:2:1)—ratio 25% TT, 50% Tt, 25% tt

THE OFFSPRINGTHE OFFSPRING

TT (tall)TT (tall)Tt (tall)Tt (tall)Tt (tall)Tt (tall)tt (short)tt (short)

PHENOTYPES3 Tall :1 Short (3:1)75% Tall, 25% Short

Cross a homozygous Cross a homozygous dominant with a dominant with a recessive (for height recessive (for height where T is dominant where T is dominant and tall).and tall).

What are my What are my genotypes?genotypes?

Cross a homozygous Cross a homozygous dominant with a dominant with a recessive (for height recessive (for height where T is dominant where T is dominant and tall).and tall).

What are my What are my genotypes?genotypes?

TT TT and and tttt

Cross a homozygous Cross a homozygous dominant with a dominant with a recessive (for height recessive (for height where T is dominant where T is dominant and tall).and tall).

Create a Punnett Create a Punnett square.square.

Cross a homozygous Cross a homozygous dominant with a recessive dominant with a recessive (for height where T is (for height where T is dominant and tall).dominant and tall).

Create a Punnett square.Create a Punnett square.

Cross a homozygous Cross a homozygous dominant with a recessive dominant with a recessive (for height where T is (for height where T is dominant and tall).dominant and tall).

Create a Punnett square.Create a Punnett square.

Cross a homozygous Cross a homozygous dominant with a recessive dominant with a recessive (for height where T is (for height where T is dominant and tall).dominant and tall).

Create a Punnett square.Create a Punnett square.

Find the percent Find the percent chance of each chance of each genotype and each genotype and each phenotypephenotype

Find the percent Find the percent chance of each chance of each genotype and each genotype and each phenotypephenotype -Tt: 100%-Tt: 100%-Tall: -Tall: 100%100%

Cross a heterozygote Cross a heterozygote with a homozygous with a homozygous recessive (for height recessive (for height where T is dominant where T is dominant and tall).and tall).

What are the What are the genotypes to cross?genotypes to cross?

Cross a Cross a heterozygoteheterozygote with a with a homozygous homozygous recessive recessive (for height (for height where T is dominant where T is dominant and tall).and tall).

What are the What are the genotypes to cross?genotypes to cross? - -Tt Tt and and tttt

Find the percent Find the percent chance of each chance of each genotype and each genotype and each phenotypephenotype

Find the percent chance of Find the percent chance of each genotype and each each genotype and each phenotypephenotype -Tt:-Tt: 50%50%-tt:-tt: 50%50%-tall:-tall: 50%50%-short:-short: 50%50%

What is the ratio of dominant: What is the ratio of dominant: recessive?recessive?

Find the percent chance of Find the percent chance of each genotype and each each genotype and each phenotypephenotype -Tt:-Tt: 50%50%-tt:-tt: 50%50%-tall:-tall: 50%50%-short:-short: 50%50%

What is the ratio of dominant: What is the ratio of dominant: recessive?recessive?2:22:2

Red is dominant to white. Using the Red is dominant to white. Using the letter R to represent red flower color, letter R to represent red flower color, make a cross between: make a cross between: homozygous dominant x homozygous dominant x

heterozygousheterozygous Find the percent chance of each Find the percent chance of each

genotype and each phenotypegenotype and each phenotype Write the ratio of Write the ratio of

dominant:recessive genotypesdominant:recessive genotypesPunnett Squares: Punnett Squares: PracticePractice

Red is dominant to white. Using the letter Red is dominant to white. Using the letter R to represent red flower color, make a R to represent red flower color, make a cross between: cross between: homozygous dominant x heterozygoushomozygous dominant x heterozygous

——RR and RrRR and Rr Find the percent chance of each Find the percent chance of each

genotype and each phenotype—genotype and each phenotype—RR: RR: 50%, Rr: 50%, Red: 100%50%, Rr: 50%, Red: 100%

Write the ratio of dominant:recessive Write the ratio of dominant:recessive genotypes—genotypes—4:04:0Punnett Squares: Punnett Squares:

PracticePractice

Brown is dominant to blue eyes. Brown is dominant to blue eyes. Using B to represent brown, Using B to represent brown, make a cross between: make a cross between: Heterozygous x heterozygousHeterozygous x heterozygous Find the percent chance of each Find the percent chance of each

genotype and each phenotypegenotype and each phenotype Write the ratio of Write the ratio of

dominant:recessive genotypesdominant:recessive genotypes

Punnett Squares: Punnett Squares: PracticePractice

Brown is dominant to blue eyes. Brown is dominant to blue eyes. Using B to represent brown, make a Using B to represent brown, make a cross between: cross between: Heterozygous x heterozygous—Heterozygous x heterozygous—Bb and Bb and

BbBb Find the percent chance of each genotype Find the percent chance of each genotype

and each phenotype—and each phenotype—BB: 25%, Bb: BB: 25%, Bb: 50%, bb: 25%, brown: 75%, blue: 25%50%, bb: 25%, brown: 75%, blue: 25%

Write the ratio of dominant:recessive Write the ratio of dominant:recessive genotypes—genotypes—3:13:1

Punnett Squares: Punnett Squares: PracticePractice

http://anthro.palomar.edu/mendel/http://anthro.palomar.edu/mendel/mendel_2.htmmendel_2.htm

Additional ResourcesAdditional Resources