Crossing over — Science definition

The exchange of matching segments between homologous chromosomes during meiosis, creating new combinations of alleles.

Where it is taught

In use

First, in crossing over, homologous chromosomes line up and swap matching segments, so a single chromosome can end up carrying a brand-new mix of a parent's alleles.

Meiosis & Sexual Reproduction

Questions using crossing over

Problem 1

Crossing over increases genetic variation because it
  1. exchanges matching segments between homologous chromosomes, creating new allele combinations
  2. copies a chromosome exactly
  3. destroys half of a cell's genes
  4. turns a body cell into a gamete without any division
Answer and explanation

exchanges matching segments between homologous chromosomes, creating new allele combinations

In crossing over, homologous chromosomes swap segments, producing chromosomes with new mixes of alleles.

Problem 2

How can crossing over generate new combinations without making new alleles?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

It exchanges segments between homologous chromosomes, rearranging existing variants.

Problem 3

Crossing over occurs between
  1. two identical copies of one chromosome
  2. homologous chromosomes paired during meiosis
  3. chromosomes and ribosomes
  4. gametes after fertilization
Answer and explanation

homologous chromosomes paired during meiosis

Paired homologous chromosomes exchange corresponding segments, producing chromosomes with new combinations of alleles.

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