Explain the process of "crossing over" in meiosis.

How is it related to genetic diversity and genetic variability?
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6 Answers

Synapsis is the pairing of homologous chromosomes before segregation. This period permits crossover. While autosomes undergo synapsis during meiosis, sex chromosomes often remain unpaired.

 

An array of proteins assembles between the two homologs. The non-sister chromatids in the tetrad align together at any point they find to match then zip together into a synaptonemal complex.

The synaptonemal complex proteins binds the homologous paired chromosomes together during prophase I of meiosis and promotes genetic recombination by the recombination enzymes that complete the crossover. This aligns the two at paired gene loci despite having different alleles for the genes.

http://www.nature.com/embor/journal/v6/n9/fig_tab/7400504_f1.html

This process of synapsis aligns the two homologous chromatids at gene loci despite having different alleles for the genes. This even aligns segments despite tandem repeat length differences

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Meiosis.html#meiosis_I

Recombination increases genetic variability within both offspring and the wider population by making new allele combinations possible despite being on the same chromosome. Crossover also provides a mechanism for repairing a damaged strand of DNA by comparison with the homologous, but intact, strand. This is a way to keep more integrity or fidelity in larger genomes.

 

by Level 2 User (700 points)
When homologous chromosomes form tetrads, they undergo the process of crossing-over. First, the chromatids of the homologous chromosomes cross oer one another. Then, the crossed sections of the chromatids- which contain alleles- are exchanged. Crossing-over therefore produces new combinations of alleles in the cells
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Crossing over happens when the homologous chromosomes line up.  When this occurs, the ends of the chromosomes may exchange segments of genetic material with their homologous pair. This contributes to genetic diversity by changing the genetic sequences on the chromosomes during meiosis so that the offspring will have a different phenotype then both of his or her parents.

 

http://www.biology-online.org/dictionary/Crossing_over
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