One of them is definitely hun
A extra genetic material at 21st chromosome i believe
No they do not have defined nucleus
Marine mammals , with few exception are viviparous.
Explanation:
- Mammals are those animals which are characterized by the presence of mammary gland and body hair.
- They feed milk to their young ones.
- The vertebrates are classified as viviparous, oviparous and ovoviviparous depending on the way their young ones develop and are nourished during their embryonic and foetal development.
- Viviparous animals are those which directly give birth to their young ones and have a distinct gestation period during which their babues develop inside their womb. These are placental mammals.
- Oviparous animals are those which lay egg and the embryo develops outside mothers body.
- Ovoviviparous animals are those who do not lay their eggs but their eggs hatch inside their body .These are aplacental animals.
- Most mammals are viviparous.
