I have 2 questions about biology involving meiosis, and RNA Splicing?

Mitosis ensures that each somatic (or body) cell that has divided contains a full set of chromosomes, termed diploid. In contrast, meiosis ensures that gametes (or sex) cells recieve only half of a full set or chromosomes, or haploid. When sperm and egg meet, they esentially fuse together to form a cell that has a full set of chromosomes: 1/2 + 1/2 = 1 full set. You cannot have more than one set of chromosomes, at least in animals. It leads to certain defects.

Introns are the non-coding regions of DNA, and exons are. When DNA is transcribed to mRNA, the introns are essentially removed from the mRNA copy, and the exons left can be recombined in any number of ways. This explains why sometimes more than one protein can be made from a single gene, and this recombination of exons is called alternative splicing.

meiosis' function is twofold: 1. to provide cells capable of uniting to result in the production of offspring that will demonstrate the continuity of the genome.( two humans each with 46 chromosomes, will undergo meiosis and then fertilization of those cells will result in a new human individual with 46 chromosomes,not 92)
2. to promote genetic diversity of gene expression---contribution of alleles from each parent, subject to Mendels laws, and by the crossing over events of synapsis in prophase I of meiosis.


As you may know the introns and exons are transcribed to the mRNA (pre-mRNA) and this transcript must be made into a functional message for expression of gene. the introns (intervening sequences) need to be spliced out. in many instances splicing involves the assocaition of snRNP's(small nuclear ribonucleoprotein complexes) which catalyze the excision of the introns leaving the significant coding portion of the mRNA, the exon free to express itself. It still has yet to be prepared to venture out into the hostile cytoplasmic environment so a 5' cap and a polyA tail are added before it can be released to the ribosome complex