Which correctly describes crossing over?
a)the process whereby nonsister chromatids exchange genetic material
b)the process whereby homologous chromosomes are pulled to opposite poles of the cell
c)the process whereby sister chromatids are pulled to opposite poles of the cell
d)the process whereby homologous chromosome pairs align randomly along the metaphase plate

Answer;

A) the process whereby nonsister chromatids exchange genetic material

Explanation;

-Crossing over is the exchange of chromosome segments between non-sister chromatids during the production of gametes. Genetically, crossover results in increased genetic variation in the chromosomes of daughter cells that result from meiosis.

-Crossing over occurs between prophase 1 and metaphase 1 and is the process where homologous chromosomes pair up with each other and exchange different segments of their genetic material to form recombinant chromosomes. It can also happen during mitotic division, which may result in loss of heterozygosity.

Crossing over is the process whereby non-sister chromatids exchange genetic material.

Further Explanation:

The chromosomal constitution of a mitotic cell chromosome behaving as a chromosome of meiosis I cell will be changed. The change in chromosomal constitution is because of occurrence of crossing over in the homologous chromosome at the prophase stage of meiosis I; this changes the genetic constitution of the chromosome.

Crossing over is the exchange of chromosome segments during the production of gametes between non-sister chromatids. The increased genetic variation in the chromosomes is a result of crossover that occurs in daughter cell at the prophase of meiosis.

Also in meiosis I, the chromosome number gets halved because of separation of homologous chromosome to the two opposite pole of the cell. This also changes the ploidy of the cell as each daughter cell formed will have n number of chromosome. So the number of chromosome itself gets changed. However, in mitosis the crossing over of chromosome does not occur and only the sister chromatids of the chromosome get separated. This leads to equal distribution of chromosomes in the daughter cell and the ploidy level of the daughter cell will remain same as that of the parents.

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Answer Details:

Grade: High School

Subject: Molecular Biology

Chapter: Gene expression

Keywords:

Meiosis, haploid, daughter cell, chromosome, crossing over, separation, chromatid, genetic variation, mitotic cell.