GENETIC DIVERSITY AND MEIOSIS I

GENETIC DIVERSITY AND MEIOSIS I - Introduction to genetics - Mendel rules - Meiosis We are talking about the change of generation and how genetic elements are behaving when they move from one generation to the next. We can think about this how our chromosomes as carries of genetic material and are moving from one generation to ne next, we have somatic cells, generative cells, we are changing between different ploidies and any polyploid organism would have the genetic set prior to the fertilization, which regenerates the original set (in this diploidy). MEIOSIS We have ancestral genomes, from mom and dad, that completes the genetic set of every one of us; the chromosomes in humans reside in the shown configuration; during meiosis there is a reduction of the set and chimeric chromosomes are form with recombination. In order to meiosis to occur, dna is duplicated, there is homolog recombination that mutually exchanges genetic elements. In the first meiotic division you separate the homologs, and in the second division the sisters chromatids are separated generating haploid cells being genetically distinct.  Inheritance The base for inheritance is the transmission of genes and their alleles (gene variants) from one generation (parents) to the next (offspring). New combinations of alleles are brought together during the meiotic divisions at the onset of the formation of generative cells. Gregor Mendel looked at single gene traits that gave a specific phenotype, like seed shape, color, and so on. He looked at these pure breads, realized that in F1 there is one dominant trait appearing and that in the segregating population was established numerically  something like a close to 3:1 ratio. If you cross two pure breads that have normally and mutant alleles, taken the first filial generation F1 all affspring have B/b genotype and normal phenotype. F2 has instead  B/b X B/b = 75% normal and 25% mutant phenotype. So, was deduced the first law of dominance and uniformity. With the plants, sometimes there is an intermediate phenotype (with co-dominance, pink roses -white x red). The last law is the law of independent assortment: genes/alleles when they segregate they do not influence each other. This is only true under certain pre-conditions, provided that they are different chromosomes -if they are the same chromosome they sort of influence each other-.    Sister chromatid cohesion and separation during meiosis We have chromosomes that come from parents, the maternal and paternal chromosomes, and once they have duplicated consist of sister chromatids and the two duplicated chromosome pairs are called homologous pair of chromosomes. We must consider that miosis I and meiosis II are two consecutive divisions during meiosis and there is not intermediate S phase; we go from a one time replication through two divisions dividing the chromosomes set by half. The first division is called reductional division, reduces the genomic content from diploid to haploid, and the second division is called equational division that is similar to mitosis. Sister chromatids are held together by cohesion molecules, there are specific subunits in miosis, and it is the force of cohesion and the force of at least one chiasma, that holds the holologs together, to counteract the spindle forces. To go through this two divisions, it is needed to keep the sisters connected where the kinetic energy is transmitted, and normally this happens at the centromeres where the kinetochore is situated, and in this reason the sister chromatine coehesin is protected. It is protected because it must undergo through a second division; nevertheless it needs to be deprotected at the arms to allow cream of the region where the chiasma has occurred. Sister chromatin cohesion is maintained around the centromeres in a specific manner that phosphorylation are specifically locally removed and that phosphorylation on the glycines sub-unit Rec8, is a prerequisite for the separase (an enzymes that cleaves this protein) to work.   MEIOSIS In telophase depending on the organism this can be longer resting state or shorter resting phase, and the nuclear membrane can reform or not, depending on the organism. These cells can have the equal right to move forward, and some some cases can lead to citolinesis or not. Then we have miosis II of the new cells from miosis I, they go through an equational divisio, forming a genetically distinct haploid cells.   The initiation of miosis recombination is the core to recombine genetic elements along the chromosomes and occurs in prophase after dna replication.