Question

crossing over
fill in the blanks...
during ____ of meiosis, __ chromosomes pair up forming a __. crossing over occurs at this time as sections of __ chromatids are exchanged. this exchange creates new combinations of alleles that results in genetic ____.
variation
tetrad
non - sister
homologous
prophase ii
sister
prophase i

Explanation:

• In meiosis, prophase I is the stage where key events occur. Homologous chromosomes (chromosomes that have the same genes in the same order, one from each parent) pair up. When they pair, they form a tetrad (a group of four chromatids - two from each homologous chromosome).
• Crossing - over specifically involves non - sister chromatids (chromatids from different homologous chromosomes). The exchange of genetic material between non - sister chromatids leads to genetic variation (new combinations of alleles, which are different forms of a gene).

Answer:

During prophase I of meiosis, homologous chromosomes pair up forming a tetrad. Crossing over occurs at this time as sections of non - sister chromatids are exchanged. This exchange creates new combinations of alleles that results in genetic variation.