A) Determine the probability that their first born will have the sickle cell trait.

1. a) Determine the probability that their first born will have the sickle cell trait. Let $\text{Hb}^\text{S}$ be the allele for sickle cell and $\text{Hb}^\text{A}$ be the normal allele. A female with sickle cell trait has the genotype $\text{Hb}^\text{A}\text{Hb}^\text{S}$. A normal man has the genotype $\text{Hb}^\text{A}\text{Hb}^\text{A}$.

Parental genotypes: $\text{Hb}^\text{A}\text{Hb}^\text{S} \times \text{Hb}^\text{A}\text{Hb}^\text{A}$
Gametes from female: $\text{Hb}^\text{A}$, $\text{Hb}^\text{S}$
Gametes from male: $\text{Hb}^\text{A}$, $\text{Hb}^\text{A}$

Punnett Square:

$$\begin{array}{|c|c|c|} \hline & \text{Hb}^\text{A} & \text{Hb}^\text{A} \\ \hline \text{Hb}^\text{A} & \text{Hb}^\text{A}\text{Hb}^\text{A} & \text{Hb}^\text{A}\text{Hb}^\text{A} \\ \hline \text{Hb}^\text{S} & \text{Hb}^\text{A}\text{Hb}^\text{S} & \text{Hb}^\text{A}\text{Hb}^\text{S} \\ \hline \end{array}$$

Offspring genotypes:
$\text{Hb}^\text{A}\text{Hb}^\text{A}$ (normal) = 2/4
$\text{Hb}^\text{A}\text{Hb}^\text{S}$ (sickle cell trait) = 2/4

The probability that their first born will have the sickle cell trait is $2/4$ or $1/2$.

\boxed{\text{1/2 or 50%}}

b) State how inbreeding leads to reduced hybrid vigour.
Inbreeding is the mating of closely related individuals, which increases the chances of offspring being homozygous for recessive alleles. This can lead to the expression of deleterious recessive alleles, resulting in a reduction in fitness, growth, and fertility, known as inbreeding depression or reduced hybrid vigour.

c) Explain how the sex of a male child is determined in human beings.
Human females have two X chromosomes (XX), producing only X gametes. Males have one X and one Y chromosome (XY), producing both X and Y gametes in equal proportions. If a sperm carrying a Y chromosome fertilizes an egg (which always carries an X chromosome), the resulting zygote will be XY, developing into a male child.

2. a) i) Identify the class to which the plant belongs. The plant shown with cones and needle-like leaves belongs to the class Gymnospermae.

ii) Give two observable characteristics that support your answer in 2(a)(i) above.

• The plant bears cones as reproductive structures instead of flowers.
• It has needle-like leaves.
• Its seeds are naked (not enclosed within a fruit).

b) State three differences between members of Kingdom Monera and members of Kingdom Plantae. | Kingdom Monera | Kingdom Plantae | | 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