Question

Unattached earlobes are dominant to attached earlobes. Cleft chin is dominant to no cleft. Parents that are heterozygous for both traits are crossed.
Determine the ratios of offspring with:
Unattached earlobes and cleft chin :
Unattached earlobes and no cleft :
Attached earlobes and cleft chin :
Attached earlobes and no cleft :

Answer 1

Answer:

Let E and e be the alleles of the genes responsible for earlobes and A and a be the alleles of the gene responsible for a cleft chin.

E is dominant over e and codes for unattached earlobes.

Similarly, A is dominant over a and codes for the cleft chin.

Both the parents are heterozygous for both the traits.

Thus, the genotype of each parent would be EeAa (unattached earlobe and cleft chin).

The gametes produced would be EA, Ea, eA, ea.

The cross would be result in the production of offspring with four possible types of phenotypes; unattached earlobes and cleft chin, unattached earlobes and no cleft, attached earlobes and cleft chin, and attached earlobes and no cleft in the ratio 9:3:3:1.

• unattached earlobes and cleft chin = (EEAA , EEAa , EeAA , EeAa , EEAa , EeAa , EeAa , EeAA , EeAa ) = 9/16
• unattached earlobes and no cleft = (EEaa , Eeaa , Eeaa ) = 3/16
• attached earlobes and cleft chin = (eeAA , eeAa , eeAA ) = 3/16
• attached earlobes and no cleft = (eeaa) = 1/16

Answer 2

Answer;

a)9:16 b)3:16 c)3:16 d)1:16

Explanation;

To complete the table;

1. EeAA
2. EEAa
3. EEaa
4. eeAA
5. eeaa

Unattached earlobes, will either be Ee (heterozygous) or ee (homozygous)

Cleft chin, will either be; AA (homozygous) or Aa (heterozygous)

Attached earlobes will be ee, while no cleft will be aa.

Therefore; the Unattached earlobes and cleft chin = 9/16

Unattached earlobes and no cleft = 3/16

Attached earlobes and no cleft = 3/16

Attached earlobes and no cleft = 1/16