The pedigree chart shows a family with a history of deafness. Analyze the inheritance pattern of deafness and answer the following questions: a) How many generations are represented in the pedigree? b

Based on the analysis in Step 1, the phenotype that is dominant is hearing.

• Bob and Ann are both hearing individuals.
• They have an offspring who is deaf.
• For two parents with a dominant phenotype (hearing) to produce an offspring with a recessive phenotype (deafness), both parents must be heterozygous carriers of the recessive allele. If deafness were dominant, at least one parent would have to be deaf to pass on the dominant allele. Since both Bob and Ann are hearing but have a deaf child, deafness must be recessive, and therefore hearing is the dominant phenotype.

Let 'A' represent the dominant allele for hearing.
Let 'a' represent the recessive allele for deafness.
A hearing individual possesses at least one dominant allele 'A'.
The possible genotypes for a hearing individual are:

• AA (homozygous dominant)
• Aa (heterozygous)

Parents: Male (XY) $\times$ Female (XX)
Gametes:
Male produces X and Y sperm.
Female produces only X eggs.

Genetic Cross (Punnett Square):

Offspring Genotypes:

• 50% XX (female)
• 50% XY (male)

This cross shows that there is an equal probability (50%) of producing a female (XX) or a male (XY) offspring, determined by the sex chromosome contributed by the sperm.

Final Answers:
2.4.1 (a): The number of generations represented in this pedigree diagram is $\boxed{\text{3}}$.
2.4.1 (b): The number of children of Paul and Lizzy who are able to hear is $\boxed{\text{1}}$.
2.4.2: The dominant phenotype is $\boxed{\text{hearing}}$.
2.4.3: Bob and Ann are both hearing, but they have a deaf son. This indicates that deafness is a recessive trait, as two individuals expressing the dominant phenotype (hearing) can produce an offspring with the recessive phenotype (deafness) if both parents are heterozygous carriers. Therefore, hearing is the dominant phenotype.
2.4.4: Using 'A' for the dominant allele and 'a' for the recessive allele, the possible genotypes for a hearing individual are $\boxed{\text{AA, Aa}}$.

Genetic cross for gender determination:
Parents: Male (XY) $\times$ Female (XX)
Gametes: Male (X, Y), Female (X)
Offspring:

Resulting genotypes: 50% XX (female), 50% XY (male).