Question

Why do a chicken embryo and a cow embryo look very similar even though the adults do not?
They are not related, but still have similar development.
They are distantly related, so their development is similar.
The embryos mutate in utero to form different structures.
The genetic makeup of the two species changes during development.

Answer 1

Correct answer: 2. They are distantly related, so their development is similar.

Explanation in brief:
- Chickens and cows are both vertebrates and share a common ancestor, so early developmental programs are conserved.
- Many embryos go through a similar “phylotypic” stage governed by conserved genes (e.g., Hox genes), producing similar features like a head, segmented body, limb buds and pharyngeal arches.
- Those similar embryonic structures are later modified by different gene expression patterns to produce very different adult forms.

Why the other options are wrong:
- 1: They are related (distantly), not unrelated.
- 3: Embryos don’t “mutate in utero” to make whole structures; mutations are rare and not the cause of normal species differences.
- 4: The DNA sequence (genetic makeup) doesn’t change during development. What changes is which genes are turned on or off (gene expression).