Heredity and Punnett Squares

Cystic Fibrosis is a recessive genetic disorder caused by a recessive allele. Cystic fibrosis is a progressive disorder characterized by excessive mucus production along the respiratory and digestive tracts in addition to other symptoms.

Elizabeth and Tony found out that they both are both carriers but do not display symptoms of the disorder. Which shows the correct probability of Elizabeth and Tony’s child having cystic fibrosis?

• 100%

• 75%

• 50%

• 25%

Answer explanation

The cross would be two heterozygous parents. So, the offspring would have a 25% chance of having the disorder.

Tags

NGSS.HS-LS3-3

Guinea pigs have a gene that codes for black or brown fur. Two Guinea pigs are bred and the result is six black offspring and two brown offspring.                                                     

In order for both black and brown offspring to be present, which of the genotypes below would yield these results?

• BB x BB

• Bb x Bb

• BB x bb

• bb xb

Answer explanation

If both phenotypes are present, neither homozygous dominant (BB) nor homozygous recessive (bb) can be present.

Tags

NGSS.MS-LS3-2

In rabbits, fur can be brown (B) or white (b). 

Cross a brown (Bb) rabbit and a white rabbit. Which of these could be true of the offspring?

• 50/50

• no chance of white fur

• 100% chance of white fur

• 100% brown babies

In chickens, rose (multiple rows/parts) is dominant over single comb. 

If a homozygous rose comb (RR) is crossed with a heterozygous female (Rr), what percentage of the offspring would have a rose comb?

• 100%

• 75%

• 50%

• 25%

Fruit flies can have normal wings (Nn or NN) or small wings (nn). 

A biologist performs a cross with two fruit flies and observes a 50/50 split of offspring with normal versus small wings. What are the likely genotypes of the parents?

• nn x nn

• Nn x Nn

• Nn x nn

• NN x NN

Tags

NGSS.MS-LS3-2

NGSS.MS-LS4-4

If HH and hh are crossed, what is the percentage of offspring that will inherit the dominant gene?

• 100%

• 80%

• 50%

• 25%

Cross AA and aa. What genotypes will the offspring have?

• Aa

• AA

• aa

• AA and aa

Tags

NGSS.HS-LS3-1

In the swallowtail butterfly, the allele for black wings (B) is dominant over the allele for yellow wings (b). A cross between two black-wing butterflies produces a yellow-wing butterfly.

What are the correct genotype and phenotype of the offspring?

• Bb, yellow wings

• bb, yellow wings

• BB, black wings

• none of these

Short tails (T) are dominant to long tails (t). 

What is the probability of a long-tailed mouse in the cross Tt x tt?

• 25%

• 50%

• 75%

• 100%

Tags

NGSS.MS-LS4-6

Which of these is the best description of an allele?

• Forms of a gene represented by letters.

• Two of the same letter, shows a recessive trait

• The trait that shows (Rr or RR)

• The chances a trait will show over another trait.