This process is called recombination, or crossover, and it is a common genetic process. Because the genes are aligned during recombination, the gene order is not altered. Instead, the result of recombination is that maternal and paternal alleles are combined onto the same chromosome. Across a given chromosome, several recombination events may occur, causing extensive shuffling of alleles.
When two genes are located in close proximity on the same chromosome, they are considered linked, and their alleles tend to be transmitted through meiosis together. To exemplify this, imagine a dihybrid cross involving flower color and plant height in which the genes are next to each other on the chromosome.
If one homologous chromosome has alleles for tall plants and red flowers, and the other chromosome has genes for short plants and yellow flowers, then when the gametes are formed, the tall and red alleles will go together into a gamete and the short and yellow alleles will go into other gametes. These are called the parental genotypes because they have been inherited intact from the parents of the individual producing gametes. But unlike if the genes were on different chromosomes, there will be no gametes with tall and yellow alleles and no gametes with short and red alleles.
If you create the Punnett square with these gametes, you will see that the classical Mendelian prediction of a outcome of a dihybrid cross would not apply. When two genes are always inherited together in this manner, it is referred to as complete linkage. Complete linkage creates only parental gametes, meaning that the gametes that are produced are chromosome copies of the parent they came from. If all genes demonstrated complete linkage during gamete formation, then the result would be that each individual chromosome in a gamete would be either a maternal or paternal replica and the offspring would show little genetic variation from their parents.
For this reason, complete linkage rarely occurs in nature and other modes of inheritance, such as crossing over , have evolved. Meiosis is a type of cell division that reduces the number of chromosomes in a parent cell by half to produce four reproductive cells called gametes.
In humans, diploid cells contain 46 chromosomes, with 23 chromosomes inherited from the mother and a second similar set of 23 chromosomes inherited from the father. Pairs of similar chromosomes are called homologous chromosomes.
During meiosis, the pairs of homologous chromosome are divided in half to form haploid cells, and this separation, or assortment, of homologous chromosomes is random. This means that all of the maternal chromosomes will not be separated into one cell, while the all paternal chromosomes are separated into another. Instead, after meiosis occurs, each haploid cell contains a mixture of genes from the organism's mother and father. Another feature of of independent assortment is recombination.
Recombination occurs during meiosis and is a process that breaks and recombines pieces of DNA to produce new combinations of genes.
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