Question:
Chromosomes are distributed randomly during anaphase I. What are the possible chromosome combinations in the two daughter cells? (Use the following abbreviations for the chromosomes. Dark green -> DG; Light green -> LG; Dark purple-> DP, Light purple -> LP)
How does the random lining up of the homologous chromosome in Metaphase 1 contribute to Genetic Variation?
Answer:
Possible chromosome combinations:
- LG,LP + DG,DP
- LG,DP + DG,LP
The random arrangement of tetrads is different in every cell going through the meiosis process. Any chromosome of the homologous pair might face any of the poles and then migrate to it. Each of the chromosomes has two possibilities for orientation at the plane. When the new haploid cells are formed, the number of variations in each cell is different and depends on the chromosomes that form that cell.
Explanation:
1) During meiosis, organisms can produce at least four different gametes. Anaphase occurs after the prophase where crossing-over has occurred. During anaphase 1, the homologous chromosomes separate, migrating to different poles.
The possible chromosome combinations in the two daughter cells of the exposed example are
- LG,LP + DG,DP
- LG,DP + DG,LP
2) Crossing-over between homologous chromosomes (prophase 1), the random lining of homologous chromosomes (metaphase 1), and random fertilization are the mechanisms involved in genetic variation.
During metaphase I, homologous pairs together migrate to the equatorial plane, where they randomly aline with their kinetochores facing opposite poles. The random arrangement of tetrads is different in every cell going through the meiosis process. There is no equal alinement between two cells. When tetrads aline in the equatorial plane, there is no predetermined order for each of the homologous chromosomes of each tetrad to face one of the poles and then migrate to it while separating. Any chromosome of the homologous pair might face any of the poles and then migrate to it. Each of the chromosomes has two possibilities for orientation at the plane. When the new haploid cells are formed, the number of variations in each cell is also different and depends on the chromosomes that form that cell. This random order in the equatorial plane is what introduces variation into the gametes. It is almost impossible that two gametes resulting from meiosis will get the same genetic charge.
