Advanced Cell and Molecular Biology - Meiosis Reduce Chromosome Number and Rearranges Genetic Information

FILAMER CHRISTIAN UNIVERSITY

Graduate School

Roxas Avenue, Roxas City

EdD SE 704        

ADVANCED CELL AND MOLECULAR BIOLOGY

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REX B. FELASOL                                                                               DR. JUDY E. GIGARE

 EdD SE Student                                                                               Professor

FINAL EXAMINATION

1. Meiosis reduce chromosome number and rearranges genetic information.

        a. Explain how the reduction and rearrangement are accomplished in meiosis.

In the reduction, homologous chromosomes pair, then separate and move to opposite poles during first meiotic division. Sister chromatids separate during the second meiotic division. Reduction can be defined as "the action or fact of making a specified thing smaller or less in amount, degree, or size." In meiosis, the amount of genetic information in the daughter cells is reduced, by half, from the amount in the parent cell. The process of reduction occurs throughout meiosis, including both Meiosis I and Meiosis II. During metaphase of Meiosis I, homologous chromosomes pair up at the mid-plate. After that, during anaphase of Meiosis I, the sister chromatids separate. Yet again in metaphase and anaphase of Meiosis II, the chromatids line up and separate. During Meiosis I, the amount of chromosomes is reduced from 2n to n. In meiosis II, the remaining set of chromosomes is divided in a mitotic way. Rearrangement plays a huge role in Meiosis, as well.

In the rearrangement process, crossing over happens. There happens a random alignment (independent assortment) of tetrads. Chromosomal rearrangement, also known as crossing-over, occurs during Meiosis I. During the first phase of meiosis, the chromosomes line up in pairs. Before the chromosomes separate, corresponding sections and/or portions of the chromosomes can switch, or cross over, between the pair. Enzymes known as recombinases assist in this process. Chromosomal rearrangement leads to genetic diversity within the offspring.

        b. Discuss how meiosis contribute to genetic variations among individuals of a species

Genetic variation is increased by meiosis. During fertilization, 1 gamete from each parent combines to form a zygote. Because of recombination and independent assortment in meiosis, each gamete contains a different set of DNA. This produces a unique combination of genes in the resulting zygote.

        c. Discuss the role that microtubules play in chromosome segregation. Name and briefly describe human disorders as a result of defect in meiotic process.

The most prominent structure in a mitotic cell is the bipolar spindle (made up of microtubules and associated motor proteins), which provides the force to move chromosomes and thereby bring about their segregation. Microtubules are nucleated by the centrosome. Microtubules are assembled from heterodimers of α-tubulin and β-tubulin, which self-assemble in their GTP-bound state into rigid tubes with an ∼25-nm outside diameter, the walls of which are built from a single layer of tubulins. Microtubules are polar, with their minus end at or near the spindle pole, and the plus end projecting away from the spindle pole. One feature that underpins the biological role of microtubules is that they are dynamic which means new subunits can be added or removed from either end. They can switch from polymerization to depolymerization (catastrophe) or vice versa (rescue) in response to GTP hydrolysis within the tubulin dimers themselves as well as the activity of associated motor proteins and regulators. Given their inherent dynamics and the existence of associated motor proteins, microtubules could theoretically contribute to chromosome segregation by acting in two ways: as a ratchet to exert pushing and pulling forces or as tracks along which cellular motors can carry chromosomes as cargo. microtubules can support directional motion in the absence of motor function