Answer:
When homologous chromosomes form pairs during prophase I of meiosis I, crossing-over can occur. Crossing-over is the exchange of genetic material between homologous chromosomes. It results in new combinations of genes on each chromosome. It is obviously another source of genetic variation in offspring.
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TRNA: transport/transfer rna
The work done is 137 joules.
Lifting opposes the acceleration of gravity, which is 9.8 m/sec/sec.
20 x 0.7 x 9.8 = 137 J (kg-m2/sec2)