Mitosis and Meiosis Questions and Answers

Answer: C

Both are true and the reason resolves the apparent paradox: a chromosome is counted by its centromeres, and replication produces two chromatids sharing one centromere until anaphase separates them. Counting by centromeres keeps the two quantities straight.

Answer: D

Homologous chromosomes pair and exchange segments at chiasmata, which is the principal source of new combinations within a chromosome. Mitosis involves no such pairing. The exchange is reciprocal, so no genetic material is gained or lost overall.

Answer: A

The paired structure is called a bivalent or tetrad, since it contains four chromatids. Nothing comparable happens in mitosis, where homologues behave independently. Pairing is what makes crossing over between homologues possible at all.

Answer: B

The chiasmata are visible under the microscope and hold the homologues together until anaphase I. Their number varies, but at least one per pair is generally needed for correct segregation. Chiasmata are the physical evidence that crossing over has taken place.

Answer: C

The chiasma physically holds the pair together so the spindle can orient them properly. Failure of this arrangement is one recognised cause of the non-disjunction that produces aneuploid gametes. Correct segregation depends on physical linkage as well as on spindle attachment.

Answer: D

Sister chromatids stay together through the first division and separate only in anaphase II. This is the essential difference between the two meiotic divisions and the commonest thing to get wrong. Homologues part first, chromatids second.

Answer: A

It separates sister chromatids without any preceding round of replication, so it is often called an equational division. Meiosis I is the reductional division that halves the number. Meiosis II needs no replication because the chromatids are already present.

Answer: B

Both are true and the reason supplies the definitions: homologues part in the first division, halving the count, whereas the second merely separates chromatids and leaves the number unchanged. Only the first division reduces the ploidy of the cell.

Answer: C

Each pair can orient in two ways, so the total is 2 raised to the 23rd power, which is 8,388,608. Crossing over multiplies the variety far beyond even this figure. The number of genetically distinct gametes is effectively unlimited.

Answer: D

Two orientations for each of 23 pairs gives 2 to the 23rd, a little over 8.3 million. Crossing over then increases the number to a point where identical gametes are effectively impossible. This is why siblings differ despite sharing both parents.