Biology 2018 Jamb Examination

Haemophilia is an X-linked recessive disorder. If a heterozygous woman (X^HX^h) marries a man with normal allele (X^HY), 50% of male offspring (XY) will inherit the affected X chromosome and express the disease, while female offspring may be carriers but not affected. Thus, 50% of their children would have haemophilia.

Cytokinesis is the process during cell division that physically separates the cytoplasm of a parent cell into two daughter cells. This ensures that each daughter cell receives the necessary organelles and cytoplasmic components to function properly, complementing mitosis which ensures genetic material is divided.

Diurnal animals are active during daylight hours and rest at night. This behavioral adaptation is linked to their feeding habits, predator avoidance, and ecological niche, distinguishing them from nocturnal animals, which are active primarily at night.

While fossil records, comparative anatomy, and geographical distribution provide evidence of evolutionary processes, mutations of genes are a mechanism that drives evolution rather than direct evidence of past evolutionary events. Thus, gene mutations alone are not considered evidence.

The diagram depicts organisms laying eggs externally, which is characteristic of oviparous species. Oviparous animals develop embryos within eggs outside the mother's body, relying on external incubation until hatching occurs.

The diagram shows a male and female amphibian in close contact with the male clasping the female, which is characteristic of amplexus. This posture ensures external fertilization in amphibians, where eggs and sperm are released simultaneously into water.

DNA analysis is the most accurate forensic tool for identifying a perpetrator because it examines unique genetic sequences. It can be obtained from hair, skin, or bodily fluids, providing conclusive evidence that links a suspect to a crime scene.

Schistosomiasis is a parasitic disease caused by Schistosoma worms, often contracted when swimming in contaminated freshwater. The parasites penetrate the skin and affect the urinary bladder or intestines, resulting in haematuria or blood in urine.

The flippers of whales and fins of fish are analogous structures that evolved independently to perform similar functions in aquatic environments. This is an example of convergent evolution, where unrelated species develop similar adaptations due to comparable selective pressures.