Question

7. INDICATE IF TRUE OR FALSE 1. Synapsis usually forms between nonsister chromatids. 2. The centrioles are highly conserved chromosome regions that interact with spindle fibers during cell division 3. Homologous chromosomes are held together in prophase I of meiosis only by crossover recombination between them. 4. Cohesin complex at the centromere keeps sister chromatids together until anaphase in both mitosis and meiosis II but not in the first meiotic division. 5. Translocation of the SRY gene from the Y chromosome onto the X chromosome results in the sex reversals in humans le ho coocotod from a dihybrid

Answer 1

1. Synapsis occurs during meiosis when crossing over takes place between chromatids. Crossing over is the process of recombination where genetic material is exchanged between two non-sister chromatids. Answer. True

2. Centrioles are independent organelles which are microtubule organizers that assist in cell division in animals. They are not part of any chromosome. Answer False.

3. Crossing over happens during prophase 1 of meiosis. But, these chromosomes are held together by Spindle fibres also. Answer False.

4. During the S phase of the cell cycle, DNA replication leads to the formation of a pair of sister chromatids with identical genetic content. The sister chromatids are physically connected through the G2 phase and begin to separate only when the cell moves from metaphase to anaphase during mitosis. The separation of chromosomes is completed in anaphase due to the loss of cohesion between the sister chromatids. This results in two daughter cells that are identical to each other and to the parent cell.

The key difference between meiosis and mitosis is that meiotic cells undergo two cell divisions, meiosis I and meiosis II, without an S phase in between. During meiosis I, the chromatin condenses as in mitosis and the sister chromatids are held together through a process called cohesion(with the help of cohesins). Unlike in mitosis, the sister chromatids remain attached at their centromeres by cohesion, and only the homologous chromosomes segregate during anaphase I. The second meiotic division is exactly like the division in mitosis, with separation of the sister chromatids. Hence, Answer is False.

5.  SRY plays an important role in the sex determination of humans and is found normally on chromosome Y. However, if it is transferred to the X chromosome, the Y chromosome will not have an SRY gene. Hence, it can no longer help in testis development. Offsprings which inherit this defective Y chromosome will have an abnormality known as Swyer syndrome, characterized by an XY karyotype and a female phenotype, as the SRY gene is absent. The X chromosome that results from this crossover will have an SRY gene. So, it will be able to initiate testis development. Such individuals have a condition called XX male syndrome, which means an XX karyotype, and a male phenotype. This is called XX male syndrome.

Hence, Answer is true

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