How does crossing over during meiosis lead to genetic variation?

1 answer:

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Crossing over happens in prophase I when the homologous chromosomes are sy naps ed. The two inner chromoatids exchanges sections with each other. This means that after the exchange the inner two chromatids have new combinations of alleles than their parents had. The two outer chromatids still have the parental combinations.So there are more kinds of chromatids ready to go into the gametes than there were before. This is an increase in variation.

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Describe both innate and acquired immune systems and the importance of vaccines.

lbvjy [14]

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Innate immunity is a non-specific immune system which provides defence against any pathogenic microorganism in early stages. It includes physical barrier such as skin, chemical barriers such as saliva, tears, et cetera, phagocytic cells such as macrophages, et cetera.

Acquired immune system is the one which develops after exposure to pathogen or antigen. It is highly specific in nature. It includes B-lymphocytes and T-lymphocytes. It includes the production of antibodies.

Vaccines are used to develop acquired immunity in people. The process is termed as vaccination or immunisation. Heat-killed or weakened pathogen or antigen is inserted into a person after which a person develops antibodies and memory cells against that pathogen or disease. So, the immune system acts more vigorously against that pathogen in secondary infection.

Thus, a person becomes immunised.

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