Which of the following best describes what happens during a cross-over event?
a) tetrads change orientation as they line up along the center of the cell.
b) chromatids of homologous chromosomes exchange corresponding segments.
c) x and y sex chromosomes overlap and combine together during metaphase.
d) spindle fibers overlap and attach to the wrong chromosomes during anaphase.

The crossover of chromosomes is the exchange of genetic material between homologous chromosomes. Homologous chromosomes are present in the meiosis I, but not in meiosis the II. After pairing up of in the prophase I, homologous chromosomes are able to exchange some corresponding segments and a cross-over occurs. Thanks to the cross-over event, each chromosome will have a new combination of genes. Without this, parents will produce gametes with only two different gene combinations.

i think its both a and b

answer: the correct option is d. enzyme

lactase and carbonic anhydrase are the examples of enzymes.

lactase is an enzyme, which is present in the small intestine of mammals. it in the digestion of the disaccharide, lactose ( milk sugar) by converting it into two monosachharide, which are glucose and galactose.

carbonic anhydrase is present in the red blood cells. this enzyme plays significant role in the transport of co₂. it in the conversion of co₂ and h₂o into carbonic acid, which is then dissociated into bicarbonate ions and hydrogen ions.