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 ratio of offspring with the described trait to the total number of offspring: unattached earlobes and cleft chin : unattached earlobes and no cleft : attached earlobes and cleft chin : attached earlobes and no cleft :

Explanation:

Step1: Fill in the missing genotypes

For the cell labeled \(1\): The parents' gametes are \(EA\) (from one parent) and \(eA\) (from the other). Using the rules of Mendelian genetics (\(E\times e = Ee\) and \(A\times A=AA\)), the genotype is \(EeAA\).
For the cell labeled \(2\): The gametes are \(Ea\) (from one parent) and \(EA\) (from the other). So, \(E\times E = EE\) and \(a\times A = Aa\), the genotype is \(EEAa\).
For the cell labeled \(3\): The gametes are \(Ea\times Ea\). \(E\times E = EE\) and \(a\times a=aa\), the genotype is \(EEaa\).
For the cell labeled \(4\): The gametes are \(eA\times eA\). \(e\times e = ee\) and \(A\times A = AA\), the genotype is \(eeAA\).
For the cell labeled \(5\): The gametes are \(ea\times ea\). \(e\times e = ee\) and \(a\times a = aa\), the genotype is \(eeaa\).

Step2: Count the genotypes for each phenotype

• Unattached earlobes (\(E-\)) and cleft chin (\(A-\)):

Count all genotypes with at least one \(E\) and one \(A\). There are \(9\) such genotypes (\(EEAA\), \(EEAa\), \(EeAA\), \(EeAa\) (counted multiple times as per the Punnett - square).

• Unattached earlobes (\(E-\)) and no cleft (\(aa\)):

Count genotypes with \(E-\) and \(aa\). There are \(3\) such genotypes (\(EEaa\), \(Eeaa\)).

• Attached earlobes (\(ee\)) and cleft chin (\(A-\)):

Count genotypes with \(ee\) and \(A-\). There are \(3\) such genotypes (\(eeAA\), \(eeAa\)).

• Attached earlobes (\(ee\)) and no cleft (\(aa\)):

Count the genotype \(eeaa\), which is \(1\) genotype.

Answer:

Unattached earlobes and cleft chin: \(9\)
Unattached earlobes and no cleft: \(3\)
Attached earlobes and cleft chin: \(3\)
Attached earlobes and no cleft: \(1\)