Understanding meiosis and its relation to lactose intolerance through genetic variation and lactase gene expression.
Extract
[...] This suggests that the arrival of this type of farming led to a change in diet, notably with the consumption of milk, and that people carrying the -13905T mutation were advantaged, which over time favored their selection. Conclusion People intolerant to lactose do not express the enzyme responsible for its degradation: lactase, which leads to digestive symptoms. Lactase is under the control of a regulatory sequence that induces a low transcription of the gene. However, a mutation of this sequence has led to obtaining people tolerant to lactose by allowing a strong transcription of this enzyme. The appearance of this mutation is linked to the appearance of cattle farming in Europe. [...]
[...] This modification affects the nucleotide 13905. In LP individuals, the nucleotide is a (thymine) whereas in LNP individuals, the nucleotide is a (cytosine). Experimentally, it has been shown that when the regulatory sequence contains a T at position 13905, the associated gene is strongly transcribed, whereas if it is a the gene is very poorly transcribed. As the presence of thymine at position 13905 corresponds to a strong transcription of the gene, it means that in these individuals, the lactase gene is strongly expressed and therefore it will be able to fulfill its role in the absorption of lactose. [...]
[...] What is lactose intolerance and what are its consequences? Lactose is the main sugar of milk. It is a disaccharide formed by the association of a glucose and a galactose. For this sugar to be absorbed by the body, it must be hydrolyzed by an enzyme: lactase. This enzyme will have the role of 'destroying' the bond between the glucose and the galactose so that the two sugars formed can be absorbed by the intestine. In the case of people who are lactose intolerant, this enzyme is not present and therefore lactose cannot be absorbed by the intestine. [...]
[...] These haploid gametes are obtained by a cellular process called meiosis. It allows to reduce the number of chromosomes by half, thanks to two phases: meiosis I and meiosis II. Meiosis I allows to reduce the number of chromosomes and meiosis II allows to separate the sister chromatids. Here's how these two phases unfold: Meiosis Reduction of the number of chromosomes This phase is itself subdivided into 4 stages: Prophase I : The DNA condenses and chromosomes with 2 chromatids become visible. They pair up in homologous pairs. [...]
[...] Each chromosome is attracted to a different pole of the cell. Telophase I : The cell divides into two daughter cells, each containing half of the originally present chromosomes. Meiosis II: Separation of sister chromatids This phase is itself subdivided into 4 stages: [...]
