User:Agarwalm2018/Sandbar shark

Reproduction
Sandbar sharks are viviparous. The embryos are supported in placental yolk sac inside the mother. Females have been found to exhibit both biennial and triennial reproductive cycles. They ovulate in early summer, and give birth to an average of eight pups, which they carry for 1 year before giving birth. The longevity of the sandbar shark is typically 35–41 years.

Sandbar sharks exhibit polyandry, where female sharks mate with multiple males. This sometimes leads to single broods of sharks having multiple fathers, also known as multiple paternity. To confirm this, 6 microsatellite genes were amplified from several litters (with known mothers) using pcr and then sequenced. All the different alleles were counted excluding the maternal alleles, and the number was used to estimate the number of fathers. This was confirmed using Bayesian analysis to estimate frequency of multiple paternity.

Ongoing research
Immune system genes, specifically MHC genes, are under study to understand the adaptive immune system in sharks such as the sandbar. Sandbars contain MHC class I, MHC class IIα, and class IIβ genes. Shark MHC genes are known to be similar to tetrapod rather than fish. Similarities include the lack of cysteines in class IIα1 domains in tetrapods and carcharhinids. Also, there are a fewer number of classical loci in sharks and tetrapods, when compared to other animals. Studies on the inheritance of MHC genes in litters with multiple paternity are being conducted to find out more about the inheritance and the evolution of the genes. It is indicated that due to the highly polymorphic nature of the MHC complex, it is highly under sexual selection in these animals.