Question

After meiosis-II daughter cells differ from the parent cells and each other in their genotypes. This can occur because of which one of the following mechanisms?
A) Only synapsis
B) Only crossing over and independent assortment of chromosomes
C) Only crossing over and chromosomal segregation
D) Crossing over, independent assortment and segregation and chromosomes

Answer 1

Hint: Crossing over causes homologous pairing and exchange of genetic material. It leads to the difference in the expression of genes and the genes differs from the parent.

Complete answer: The Mendel gave three laws of inheritance: the law of segregation, the law of independent assortment and the law of dominance. The law of segregation states that only one allele from the parent cell enters the offspring and thus, they are not identical from the parent cell. The law of assortment independent states that one allele that enters is assorted in one pair irrelevant to their bond in between. The crossing over occurs in the prophase of the cell division specifically in prophase I of meiosis. The crossing over is the exchange of small segments between the homologous pairs of duplicated chromosomes and this stage is called bivalent formation. The exchange of segments is important as they make the offspring little different from the parent’s genome. This phenomenon plays an important role in adaptation, mutation or evolution. Crossing over occurs in the pachytene stage of the prophase I of meiosis I. It leads to recombination in organisms. It is a phenomenon that occurs only in germ cells.
Thus, the correct answer is option D.

Note: The crossing over is different from synapsis. Synapsis is the process of pairing the homologous which can be sister chromatids or non-sister chromatids. Crossing over occurs during synapsis. In this process, a segment of the chromosome gets exchanged with non-sister chromatids.