The Effect of Crossing Over on Chromosomes

Chromosomes are very careful about crossing over. If they notice that the genes aren't in the right order, from A to Z, they will not cross over. In these sparrows, a huge chunk of chromosome two had been inverted. The white-stripe mutation and the more aggression mutation therefore stayed together. And here's the payoff. Can you guess which animals do not cross over? That's right. The sex chromosomes.