1 Analyze the pedigree chart and determine the phenotype and genotype of Senzo and Thuli, and explain the inheritance of colour-blindness.

Senzo is represented by a filled square.

A filled square indicates a colour-blind male.
The phenotype of Senzo is:

• Colour-blind male

Thuli is a normal female.

Thuli has a colour-blind daughter, Linda ($\text{X}^{\text{d}}\text{X}^{\text{d}}$), and a colour-blind son, Senzo ($\text{X}^{\text{d}}\text{Y}$).

The genotype of Thuli is:

• $\boxed{\text{X}^{\text{D}}\text{X}^{\text{d}}}$

Molly is a normal female. Her mother is Thuli ($\text{X}^{\text{D}}\text{X}^{\text{d}}$) and her father is a colour-blind male ($\text{X}^{\text{d}}\text{Y}$). Molly must have inherited $\text{X}^{\text{D}}$ from her mother and $\text{X}^{\text{d}}$ from her father. So, Molly's genotype is $\text{X}^{\text{D}}\text{X}^{\text{d}}$.

A normal male has the genotype $\text{X}^{\text{D}}\text{Y}$.

Parents: $\text{X}^{\text{D}}\text{X}^{\text{d}}$ (Molly) $\times$ $\text{X}^{\text{D}}\text{Y}$ (Normal male)

Gametes from Molly: $\text{X}^{\text{D}}$, $\text{X}^{\text{d}}$
Gametes from Normal Male: $\text{X}^{\text{D}}$, $\text{Y}$

Possible Genotypes and Phenotypes of their children:

• Genotypes:

  • $1/4$ $\text{X}^{\text{D}}\text{X}^{\text{D}}$
  • $1/4$ $\text{X}^{\text{D}}\text{X}^{\text{d}}$
  • $1/4$ $\text{X}^{\text{D}}\text{Y}$
  • $1/4$ $\text{X}^{\text{d}}\text{Y}$

• Phenotypes:

  • $1/2$ Normal females ($1/4$ homozygous normal, $1/4$ carrier)
  • $1/4$ Normal males
  • $1/4$ Colour-blind males