Question

In humans, earlobes are either "free" or "attached". The free earlobe traits is dominant over attached earlobes. The ability to taste certain substances is also genetically controlled. Some people can taste Phenylthiocarbamate (PCT), a dominant trait, while others cannot (the recessive trait).

A man heterozygous for both free earlobes and ability to taste PCT has children with a woman with attached earlobes who is heterozygous for the ability to tate PCT. Show all work including a Punnet square below. E= free earlobes; e= attached earlobes; P= PCT taster; p= non-PCT taster.

a. What are the genotypes of the parents?

Male's genotype:
Female's genotype:

What are the possible gametes for each parent?

b. Complete the Punnet Square to determine the genotypes and phenotypes of their children.

c. What is the phenotypic ratio for this cross? Be sure to write out phenotypes.

Answer 1

A heterozygous man with free earlobes and the ability to taste PCT mates with a heterozygous woman with attached earlobes. The Punnett square yields a phenotypic ratio of 9:3:3:1 for free earlobes, PCT taster; free earlobes, non-PCT taster; attached earlobes, PCT taster; and attached earlobes, non-PCT taster, respectively.

a. Genotypes of the parents:

Male's genotype: EePp

Female's genotype: EePp

Possible gametes:

Male: EP, Ep, eP, ep

Female: EP, Ep, eP, ep

b. Punnett Square:

| EP | Ep | eP | ep |

--------|----|----|----|----|

EP | EEPP | EEPp | EePP | EePp |

Ep | EEPp | EEpp | EePp | Eepp |

eP | EePP | EePp | eePP | eePp |

ep | EePp | Eepp | eePp | eepp |

c. Phenotypic ratio:

Free earlobes, PCT taster: 9

Free earlobes, non-PCT taster: 3

Attached earlobes, PCT taster: 3

Attached earlobes, non-PCT taster: 1