Punnett Squares

Punnett Squares

Punnett Squares are used to predict the genotype of offspring from different crosses.

​Dominant

Recessive

Heterozygous

Homozygous

B

b

B

b

bb

BB

Bb

Bb

An Allele is a variant form of a gene that is shown by a capital or lowercase letter.

​Ex: In a dog, black is dominant (B) to brown which is recessive (b)

Heterozygous = different alleles (Bb)

Homozygous = same allele (BB, bb)

Multiple Choice

What is the purpose of Punnett Squares?

• To see how many offspring there will be

• To see which alleles are dominant

• To predict the potential genotypes of the offspring of a particular cross

• To see alleles

Fill in the Blanks

If 1 out of 4 offspring are homozygous recessive, what percent is this? $\left(1\div4\right)\times100=?$

Multiple Choice

What percent of offspring are heterozygous?

• 25%

• 50%

• 75%

• 100%

Multiple Choice

What percent of offspring are homozygous recessive?

• 0%

• 25%

• 50%

• 75%

Draw

Fill in the missing alleles.

Multiple Choice

B = brown fur

b = white fur

In the Punnett Square, what is the probability for white fur? 

• 50%

• None will have white fur

• 25%

• 100%

Genotype vs. Phenotype

Genotype: the combination of alleles one possesses for a certain gene

Ex: BB, Bb, bb

Phenotype: the observable characteristics or traits that are influenced by the genotype

Ex: Brown Eyes vs Blue Eyes

​Ex: If B is dominant for brown eyes, and b is recessive for blue eyes, anyone with the genotype BB OR Bb would have brown eyes whereas the genotype bb would result in blue eyes

Multiple Choice

_____ is the genetic makeup of an organism.

• Genotype

• Phenotype

Multiple Choice

_____ is the physical appearance of an organism.

• Genotype

• Phenotype

Multiple Choice

In a heterozygous genotype, the ___________ allele takes over in the phenotype.

• Both the recessive and dominant alleles

• Recessive

• The lowercase letter

• Dominant

Multiple Choice

In a flowering plant species, red flower color (R) is dominant over white flower color (r). What is the genotype of any red-flowering plant resulting from this species?

• Rr

• RR

• RR or Rr

• rr

Draw

Fill out the Punnett Square, given that one parent has a homozygous recessive genotype and the other has a homozygous dominant genotype. Complete to find fur color of the offspring, where B is brown hair and b is white hair.