What will happen to DNA when astronauts return to Earth?American scientists tell you the answer

Human exploration of space is deepening.For astronauts,in space,not only will they face various threats,but also the risk of mutation of genes in the body due to exposure to cosmic rays.So,what will happen to DNA after a year in space?American scientists have done such experiments.They have selected a pair of genetically similar twin astronauts and sent their brother to the International Space Station， while his brother stayed on Earth.A year later,the younger brother returned to the earth.By comparing with his brother,he found that the younger brother not only had a great change in appearance and height,but also had a corresponding change in about 7% of the DNA sequence.