You understand correctly that we are talking about sexual production, which is the mating of genetic matter of the different parents, depending on the reproductive cells, ovals, and spermatozoid. In each contents half of the parental genome of 23 chromosomes, such a production is the basic of evolution and genetic variation. Sexual production is necessary for the survival of all species, such as humans. For us humans, each reproduction sells contents 23 chromosomes, half of the initial complete set. And chromosomes from one parent must pair with the same chromosome of the other parent. Chromosomes use it to brew genetic information before splitting new ones into, then to form four reproductive cells with different genetic background. This process answers various variations in the reproduction cells. It is this process that makes you different from your sister or brother. Every human body contains 23 pairs of chromosome beaming the genes in the nucleus of each cell with genetic baggage. Chromos impart from the mother 23 chromosomes and from father 23 chromosomes with the 23rd pair is different by gender, femal, inherit one X chromosome from each parent, mole have Y chromosome from the father and X chromosome of the mother. So femal are X, X and mole X, Y. And it's the best important thing to remember. In some species like drosophilus example, sex is determined by the number of X. This hypothesis is contradicted by the observation of chromosomal abnormalities affecting in the number of sex chromosomes. Eterozuma abnormalities, we observe a number of abnormalities in the number of sex chromosome presented by some individual which present a mild or femal phenotype which means that the phenotypic sex of the individual does not seem to be related to the number of X's. But rather to the presence or absence of Y. This gives a fundamental role in determining sex, sexual inversions. We observe some rare cases of birth of antiris antirsexual, individual that is presenting a sexual inversion. Their sexual phenotypic does not correspond to the sex chromosomes observable in their triotip, mole X, X, one in 20,000 birth. Femal X, Y, one in 10,000 birth. This phenomena is explained by events of mutation of drosolocation. In fact, the X and Y chromosomes present homologous regions at the ends of their arms. Also do autosomal region par one on the short arm and pair two on the long arm. Sexual inversion does come from in fact the drosolocation of a factor of the level of the pair one region during muzzices cell multiplication by crossing over. Between the X and Y chromosomes, this factor was named a tested determining factor, TDF. Look at it just below pair one or homologous region one. Later it was shown that the TDF was actually a single gene called S, Y, sex determining region. This gene is expressed during the sexual development of the gonads and the more in the case of translocation, it would be disintegrate on the Y chromosome or added on the X chromosome say mutations in the gene S, Y, making it no functional, leading to the obtaining of individual X, Y, but of a formal phenotype. The gonadol determinants therefore depends on the presence of S, Y, Gen, the S, Y protein has a high mobility group as M, M, G, domain that allows it to, but to data. During sperm formation there may be bricks in chromosomal area and DNA fragmentation and may sell elsewhere on another chromosome. The S, Y, Gen is localized on the Y chromosome, sometimes it is found in individual with 46 Y chromosome 2 of which are 6-uel X, X, with the S, Y, grew it at the end of one of the X's. The simplified things so we have X, Y, individual, but formal phenotypic, but formal phenotyp and X, X, individuals, but of mild phenotyp. And most important to remember and beside this you will ask me why this recall, simply it will be useful to you in the next video.