Biological termHard1 mark
1(a)
Name the following:
The exchange of chromatid parts between the maternal and the paternal chromatids of a pair of homologous chromosomes during meiosis.
Topic: Crossing over
Previous-year question practice database
Answer
Exam answer
CROSSING OVER.
Explanation
Crossing over occurs during PROPHASE I of MEIOSIS. The homologous chromosomes lie side by side, their chromatids touch at points called CHIASMATA, and segments are exchanged between the maternal and paternal chromatids.
WHY IT MATTERS: it produces NEW COMBINATIONS of genes that existed in neither parent. Together with the independent assortment of chromosomes, it is the chief source of VARIATION among offspring — which is why brothers and sisters differ from one another.
Note that it happens only in MEIOSIS, never in mitosis. Mitosis produces daughter cells IDENTICAL to the parent; meiosis is designed to produce difference.
More from Structure of Chromosomes, Cell Cycle and Cell Division
A sequence of DNA has 300 nitrogenous base pairs, of which 75 are Guanine. What is the number of Thymine in this sequence?2026Which is the resting but metabolically active stage of the cell cycle?2026Mention the number of Autosomes and Allosomes in a human body cell.2026Draw a neat, labelled diagram of an animal cell showing the Prophase stage of Mitosis with four chromosomes.2026Differentiate between Mitosis in a plant cell and an animal cell based on Cytokinesis.2026A phase of cell division where the spindle fibres disappear is:2025