crossing over
crossing over
or cross·ing-o·ver (krô′sĭng-ō′vər, krŏs′ĭng-)crossing over
cross′ing o′ver
n.
| Noun | 1. |  crossing over - the interchange of sections between pairing homologous chromosomes during the prophase of meiosis |
n.
crossing over
crossing over,
process in genetics by which the two chromosomeschromosome, structural carrier of hereditary characteristics, found in the nucleus of every cell and so named for its readiness to absorb dyes. The term chromosome
..... Click the link for more information. of a homologous pair exchange equal segments with each other. Crossing over occurs in the first division of meiosismeiosis
, process of nuclear division in a living cell by which the number of chromosomes is reduced to half the original number. Meiosis occurs only in the process of gametogenesis, i.e., when the gametes, or sex cells (ovum and sperm), are being formed.
..... Click the link for more information. . At that stage each chromosome has replicated into two strands called sister chromatids. The two homologous chromosomes of a pair synapse, or come together. While the chromosomes are synapsed, breaks occur at corresponding points in two of the non-sister chromatids, i.e., in one chromatid of each chromosome. Since the chromosomes are homologous, breaks at corresponding points mean that the segments that are broken off contain corresponding genesgene,
the structural unit of inheritance in living organisms. A gene is, in essence, a segment of DNA that has a particular purpose, i.e., that codes for (contains the chemical information necessary for the creation of) a specific enzyme or other protein.
..... Click the link for more information. , i.e., alleles. The broken sections are then exchanged between the chromosomes to form complete new units, and each new recombined chromosome of the pair can go to a different daughter sex cell. Crossing over results in recombinationrecombination,
process of "shuffling" of genes by which new combinations can be generated. In recombination through sexual reproduction, the offspring's complete set of genes differs from that of either parent, being rather a combination of genes from both parents.
..... Click the link for more information. of genes found on the same chromosome, called linked genes, that would otherwise always be transmitted together. Because the frequency of crossing over between any two linked genes is proportional to the chromosomal distance between them, crossing over frequencies are used to construct genetic, or linkage, maps of genes on chromosomes. Mutationsmutation,
in biology, a sudden, random change in a gene, or unit of hereditary material, that can alter an inheritable characteristic. Most mutations are not beneficial, since any change in the delicate balance of an organism having a high level of adaptation to its environment
..... Click the link for more information. , temperature changes, and radiation all affect crossing over frequency. Under the microscope, a crossover has the appearance of an X and is called a chiasma.
crossing over
crossing over
crossing over
orcrossing-over
(krô′sĭng-ō′vər, krŏs′ĭng-)crossing over
Recombination Vox populi A popular phrase for a change in a person's sexual preference, usually heterosexual → homosexual
crossing over
a process occurring in the DIPLOTENE stage of Prophase 1 of MEIOSIS in which there is exchange of nonsister CHROMATIDS, producing genetic RECOMBINATION. (see Fig. 123 ). See also UNEQUAL CROSSING OVER.crossing over
- noun
Synonyms for crossing over
noun the interchange of sections between pairing homologous chromosomes during the prophase of meiosis
Synonyms
- crossover
Related Words
- diplotene
- biological process
- organic process