Bonobos, gorillas, and gibbons form the most closely related grouping.

There seems to be no relationship between these species.

The least closely related to humans seem to be gorillas and orangutans.

Humans are more closely related to chimps than to bonobos.

Hydrostatic skeleton = 1, exoskeleton = 2, endoskeleton = 3.

Hydrostatic skeleton = 2, exoskeleton = 3, endoskeleton = 1.

Hydrostatic skeleton = 1, exoskeleton = 3, endoskeleton = 2.

Hydrostatic skeleton = 3, exoskeleton = 1, endoskeleton = 2.

The gonad is bipotential so it can form either ovaries or testes.

Gonads that differentiate into testes secrete testosterone and drive male sex organ development.

Female-specific sexual organs arise from Mullerian ducts.

Sex steroid synthesis cascade modifies cholesterol into testosterone or estrogens.

modify testosterone so it cannot efficiently bind to its receptor.

block or alter the structure of the androgen receptors.

alter the activity of enzymes that synthesize sex steroids.

block the uptake of cholesterol so sex steroids can’t be produced.

It allows for high and different pressures in the systemic and pulmonary circuits.

It allows for complete separation of oxygenated and deoxygenated blood.

It allows the blood to flow directly from the lungs to the organs and extremities.

It allows for complete separation of systemic and pulmonary circulation.

Hagfish and lungfish.

Lampreys and lungfish.

Caecilians and coelacanths.

Sharks and rays.

When the ratio of X chromosomes to autosomes is 2:2.

When the ratio of X chromosomes to autosomes is 1:2.

Due to the presence of sex determining genes on the Y chromosome.

As a result of spontaneous loss of the Y chromosome.