Transmission, Variation and Expression of Genetic Heritage
Cours : Transmission, Variation and Expression of Genetic Heritage. Recherche parmi 298 000+ dissertationsPar Youssef Bargach • 15 Décembre 2023 • Cours • 762 Mots (4 Pages) • 63 Vues
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L. B. / 2023 – 2024
SVT 1ère / Chapter 1
Theme1: Transmission, Variation and Expression of Genetic Heritage
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« Cell Divisions in Eukaryotes »
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A-‐ Mitosis
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-‐ In eukaryotes, a cell cycle begins with the G1 phase, during which chromosomes are made up of one chromatid, or one DNA molecule. Then, the chromosomes duplicate identically, during the S phase. During the G2 phase, the duplication is completed: all the chromosomes consist of two identical sister chromatids. During the M phase, the sister chromatids of each chromosome separate and migrate to opposite poles of the mother cell. This process is guided by the mitotic spindle. Then the cell divides into two daughter cells.
-‐ Mitotic cell division is therefore a conformal reproduction. The succession of mitoses produces a set of cells, all genetically identical, called a clone. All the characteristics of the karyotype of the parent cell (number and morphology of the chromosomes) are preserved in the two daughter cells.
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L. B. / 2023 – 2024 | ||
SVT 1ère / Chapter 1 | ||
B-‐ | Meiosis: | |
-‐ | Meiosis consists of two successive cell divisions. It is preceded, as for mitosis, by an S | |
-‐ | phase forming chromosomes with two identical sister chromatids. | |
The first division leads to the separation of pairs of homologous chromosomes, | ||
genetically different. Then, these cells divide again: the sister chromatids of each | ||
homologous chromosome separate. The meiotic spindle set up during these two | ||
successive divisions ensures the migration of the chromosomes to the opposite poles of | ||
-‐ | the cell. | |
Meiosis thus leads to four haploid cells, each with half the chromosomes of the initial | ||
diploid cell. | ||
Diploid(2n) | ||
Haploid(n) | ||
-‐ | Videos: | |
Comparaison entre mitose et méiose | ||
-‐ | https://www.youtube.com/watch?v=nGUpNld5L7c | |
Les étapes du Cycle Cellulaire (Mitose & Méiose) | ||
https://www.youtube.com/watch?v=AIzjdpEhjbc | ||
C-‐ | The Composition and Structure of Chromosomes | |
-‐ | A chromosome is made up of one or two DNA molecules, depending on the phase of | |
the cell cycle in which it is found, and of proteins. A DNA molecule is composed of two | ||
long strands of DNA associated and wound in a double helix. Each strand is a succession | ||
of nucleotides (Adenine, Cytosine, Guanine and Thymine) linked together by covalent | ||
bonds. The nitrogenous bases of one strand are linked to the nitrogenous bases of the | ||
other strand: guanine always associates with cytosine and adenine always associates | ||
with thymine. This pairing leads to the description of these bases as complementary. | ||
-‐ | In eukaryotes, DNA undergoes alternating condensation (M phase) and decondensation | |
(G1, S, G2 phases), thanks to the intervention of proteins. |
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