Monday, June 27, 2011

Physiology secrets



PHYSIOLOGY SECRETS
Beyond Mendel’s law (variation in Mendelian genetics)
There are 2 common variations.
1. Blood types-Mendel studied, each character is determined by a gene with 2 alleles, i.e 2 alternate forms. But in blood types ,unlike the genes Mendel studied, which had only 2 alleles, the blood type gene I exists in 3 distinct forms. The 3 alleles are IA, IB, IO.The A and B alleles are co-dominant, and both are completely dominant to O.However, even though 3 possible alleles in human, an individual can have only 2 of the alleles in his or her genes. And 4 possible blood types exist.
2.Maternal inheritance and Mitochondrial genes- The basis of the law of segregation is that both parents contribute genes equally to offspring. But in the case of mitochondria, it is interesting to note that the genes in the mitochondria are inherited only from mother. Why not from father? Because mitochondria are located in the middle of the sperm not in the head region that enter the egg. In rare instances, when mitochondria from sperm enter an oocyte they are destroyed selectively early in embryonic development.

Friday, June 24, 2011

physiology secrets



PHYSIOLOGY SECRETS
Reasoning out: Single gene traits obey All or None Law-comment
Yes. Single gene traits are discrete or qualitative and providing All or None phenotype (normal vs. affected) instead multiple genes that regulate height, skin colour-result in continuously varying phenotype. (Skin colour is controlled by 8 genes)Both single gene and polygenic traits can also be multifactorial i.e. they are influenced by environement.pure polygenic not influenced by environment are rare. (Eye colour-polygenic not environmental)