Question

Select ALL the correct answers.
Which of the following could be evidence that an organism's growth is influenced by the organism's genes?

(Hint: Identical twins have identical genes. Non-identical twins have about half the same genes.)

Children are likely to have friends who are about the same height.
Identical twins are more likely to be about the same height than non-identical twins.
A dog breed can be made smaller by breeding together only the smallest dogs.
Identical twins often have slightly different weights at birth.

Answer 1

Correct answers:
- Identical twins are more likely to be about the same height than non-identical twins.
- A dog breed can be made smaller by breeding together only the smallest dogs.

Why:
- If identical (monozygotic) twins, who share the same genes, are more similar in height than non-identical (dizygotic) twins, that pattern supports a genetic influence on height.
- Selective breeding (choosing the smallest dogs to breed) changing the average size of a breed shows that size is heritable — controlled at least partly by genes.

Why the others are not good evidence:
- Children having friends of about the same height can be explained by social/environmental factors (same age, same school), not genes.
- Identical twins having slightly different birth weights shows environmental effects (e.g., placental differences) despite identical genes, so it does not support a genetic-only explanation.