Question

Last week you were wondering what Jessica and Tom's babies might look like with respect to their eyebrows and earlobes (both Tom and Jessica have thick eyebrows, controlled by gene E, with thick eyebrows dominant to thin eyebrows and both of them have free earlobes, controlled by gene F, with free earlobes dominant to attached earlobesi You know that Tom's mom has attached earlobes. Additionally. Tom's mom has thin eyebrows, and so does Jessica's dad. No one in Jessica's pedigree going back to her great grandparents are known to have had attached earlobes, so you assume that she must be homozygous for this trait.

Please help me understand. My thoughts are A and F, but that is an incomplete answer.

Answer 1

Representation:

1. Trait 1: Eyebrows thchness

Thick eyebrows= Dominant = EE (homozygous)/ Ee (heterozygous)

Thin eyebrows = Recessive = ee

2. Trait 2: Earlobe type

Free earlobe = Dominant =FF/Ff

Attached earlobe = recessive = ff

In case of Tom:

· Tom has Thick eyebrows and free earlobes

· Tom’s mom has attached earlobes and thin eyebrows

· Thus, Tom is heterozygous for both traits.

· Genotype of Tom = EeFf

In case of Jessica:

· Jessica has Thick eyebrows and free earlobes

· Jessica’s dad has thin eyebrows

· Thus, Jessica is heterozygous for Eyebrows.

· Probable genotype of Jessica= EeFF

· However, the child has thin eyebrows and attached earlobes.

· Thus, genotype of child is eeff

· Hence, Jessica’s genotype is EeFf. This indicates that one of Jessica’s ancestor and her parents are carrier for attached earlobe.

· Thus, Jessica’s genotype = EeFf

Cross: EeFf x EeFf

	EF	Ef	eF	ef
EF	EEFF	EEFf	EeFF	EeFf
Ef	EEFf	EEff	EeFf	Eeff
eF	EeFF	EeFf	eeFF	eeFf
ef	EeFf	Eeff	eeFf	eeff

eeff = 1/16.

Answer: options a and d