Final answer:
Bird genomes differ from mammalian genomes primarily in size and non-coding DNA content, where birds have more compact genomes. Despite differences, birds and mammals share significant genetic similarities due to their vertebrate ancestry. Whales and horses, being mammals, share more DNA sequences than whales and sharks.
Step-by-step explanation:
When comparing bird genomes to those of mammals, we find that there are both similarities and substantial differences. Both birds and mammals are part of the vertebrates and thus share a significant number of genes and DNA sequences. This commonality reflects their shared ancient ancestry. However, the overall structure and size of bird genomes can be quite different from those of mammals. Birds tend to have more compact genomes with less non-coding DNA and fewer repetitive elements. An example of these differences is evidenced through comparative analysis, where certain structural domains may be shared between proteins across species, despite having different functions.
Addressing which animals would have more DNA sequences in common, between a whale and a horse, or a whale and a shark, it's important to note that the whale and the horse are both mammals and therefore share a more recent common ancestor as opposed to the whale and the shark, which diverged earlier in evolutionary history. Hence, a whale and a horse would share more DNA sequences in common. Moreover, when we look at different species, such as a mammal and a bird, or a mammal and a fish, we can predict a mammal will have more molecular differences with a bird than with a fish due to the different times of divergence from a common ancestor.