Punnett Squares

BELL RINGER

What do these pictures show?What is unusual about this hand and foot? Look closely!!

BELL RINGER CONT.

•The hand and foot have six fingers and toes instead of five.

•This is the result of a genetic disorder referred to as Polydactyly – having more than five digits.

BELL RINGER CONT.

What religious group do these people

belong to?

They are Amish - lead a simple life centered on

family and religion. Large population resides in Lancaster County, PA.

BELL RINGER CONT.The Amish live separately from the

rest of society.

They typically marry only other Amish

people. What if I told you Polydactyly is more

common among the Amish than in the

general population. Why do you think that

is true?Why might it someday be important for you to know if you are a carrier for a genetic disease?

A Model used to show the possible ways genes can combine during fertilization.

Helps you keep track of traits.

Punnett Squares

.

Dominant and recessive alleles

are represented by letters.

Punnett Squares

A capital letter (T) is used for dominant alleles.

Punnett Squares

A lowercase letter (t) is used for recessive alleles.

Punnett Squares

If you wanted to know the type of offspring a cross between two parents would produce, you can use a punnett square.

Tt x Tt

TT,Tt for tall

Tt for short

Punnett Squares

The letters representing the alleles from one parent are placed along the top of the square.

T t

Punnett Squares

The letters representing the two alleles from the second

Parent are places along the side of the square.

T

t

Punnett Squares

T t x T t

T t

T

t

Punnett Squares

Punnett Squares

Squares are filled by writing the letter at the top beside the letter on the side.

TT Tt

Tt t t

T t

T

t

Punnett Squares

The letters in each of the squares represents the Genotypes of the offspring that the parents could produce.

TT Tt

Tt t t

T t

T

t

TT

Tt

Tt

t t

The genotype (genetic makeup) can be used to predict the phenotype (physical appearance) of the offspring.

Punnett Squares

Necessary Definitions

Homozygous: same two alleles Heterozygous: One of each allele

Genotype PhenotypeTT: Homozygous dominant tall

Tt : Heterozygous tall

Tt : Heterozygous tall

t t : Homozygous recessive short

Punnett Sqaures

Punnett Squares

Probability: the ratio that a particular event could occur.

You can give genotypic ratios and phenotypic ratios

out of 4 offspring

3 would be tall

1 would be short

Punnett Squares

TT Tt

Tt t t

T t

T

t

TT

Tt

Tt

t t

Give the phenotypic and genotypic ratio of this cross

Look at the F1 generation and count each type Genotypic: 1(TT): 2 (Tt): 1 (tt) Phenotypic: 3 (Tall): 1(short)

Punnett Squares:

•Help you keep track of traits.

•Predict genotype and phenotype.

•Calculate probability.

WHAT IS PROBABILITY?Probability is the likelihood that a particular event will

occur

Example: A coin flip

What are the possible outcomes when you flip a

coin?

Answer: There are two – it could land heads up or tails up

WHAT IS PROBABILITY? CONT.Probability is the likelihood that a particular event will

occur

Example: A coin flip

What are the chances a coin will land heads up?

Answer: 50% or ½

What are the chances a coin will land tails up?

Answer: 50% or ½

WHAT IS PROBABILITY? CONT.

If you flip a coin 3 times in a row, what is the probability it will land heads up

every time?Each coin flip is an independent event – each

time the coin is flipped, the probability of it landing heads up is ½ .

The probability of flipping 3 heads in a row is:½ x ½ x ½ = 1/8

Remember: Past outcomes do not effect future outcomes!

HOW DOES PROBABILITY RELATE TO GENETICS?

The principles of probability can be used to predict the outcomes of genetic crosses!

Coin Toss Lab• Click here to practice your probability skills