During a single crossover event, how many strands of dna must break? (recall that dna is double-stranded.)

Answer;

Four strands

Explanation;Cross over is the process which takes place during meiosis type of cell division in the prophase I stage of meiosis I. During this process, non sister chromatids of the homologous chromosomes pair at a point called chiasmata and exchange genetic materials. During cross over the non sister chromatids of homologous chromosomes are exchanged which means four chromatids must break for the process to take place. Cross over is an important process as it causes genetic variation and hybrid vigor among organisms that reproduce sexually,

The answer is hilum.

A  reaction  in which  energy  is  released  to the surroundings is called an exothermic  reaction. in this type of  reaction  the enthalpy, or stored  chemical energy, is lower for the products than the reactants. when ammonium nitrate is dissolved in water,  energyis  absorbed  and the water cools.