Biology, Eighth Edition (Raven)

Chapter 42: Plant Reproduction

Meiosis with Crossing Over

How are genes on the same chromosome inherited? An important fundamental of genetics is the idea of independent assortment. This states that genes are inherited independently of one another. Imagine an individual has two different alleles (versions of a gene) for eye color (blue and brown) and two different alleles for hair color (blonde and black). If a gamete produced by that individual contains the blue eye color allele it is has an equally good chance of containing the blonde or the black hair color allele. This can be true even if both genes are on the same chromosome. Chromosomes segregate during Meiosis I and you might expect that all genes on a chromosome would be inherited as a unit. However, during prophase I homologous chromosomes pair up and become attached to one another. At this time, crossing over moves sections of DNA between homologous chromosomes and allows for independent assortment.

View the animation below, then complete the quiz to test your knowledge of the concept.


A crossover in meiosis is an exchange of genetic material between
A)sister chromatids of the same chromosome.
B)sister chromatids of homologous chromosomes.
C)sister chromatids of non-homologous chromosomes.
D)non-sister chromatids of homologous chromosomes.
E)non-sister chromatids of non-homologous chromosomes.

A tetrad is made up of
A)four non-homologous chromosomes.
B)four non-homologous chromatids.
C)four homologous pairs of chromosomes.
D)two homologous pairs of chromosomes.
E)two homologous chromosomes, each consisting of two chromatids.

Which of the following statements about crossing over is TRUE?
A)It occurs only in males.
B)It occurs only in some chromosomes.
C)It occurs only between genes that are heterozygous.
D)It results in reduced genetic variation among gametes.
E)None of the above

Crossing-over occurs during prophase I of meiosis.

Crossing-over allows the reassortment of linked genes.
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