The crossing over that causes genetic recombination occurs during which substage of meiosis?
A. Diplotene
B. Zygotene
C. Pachytene
D. Leptotene
Answer: Option C
Solution (By JKExamLibrary)
Crossing over, the exchange of genetic material between non-sister chromatids of homologous chromosomes, occurs during the pachytene stage of prophase I. The synaptonemal complex facilitates this. Chiasmata become visible in diplotene when the synaptonemal complex dissolves. Leptotene is chromosome condensation, zygotene is synapsis. This process is crucial for genetic variation.
Explanation:
Spectrophotometry quantifies the concentration of a substance by measuring the absorbance of light at specific wavelengths. Chromatography separates mixtures, electrophoresis separates charged molecules, centrifugation separates by density/size. Spectrophotometers are widely used in biochemical and clinical labs.
Explanation:
Individuals with blood group 'O' have red blood cells that lack both A and B antigens on their surface. Because there are no antigens to react with the recipient's antibodies, their blood can be safely transfused to individuals of any ABO blood group in emergencies. However, their plasma contains both anti-A and anti-B antibodies.
Assertion (A): Genetic variation is essential for evolution.
Reason (R): Without variation, natural selection cannot occur because there are no differences to select from.
A.A false, R true.
B.Both A and R are true, but R is not the correct explanation.
C.Both A and R are true, and R is the correct explanation.
Explanation:
Genetic variation provides the raw material for natural selection. If all individuals were identical, selection could not favor any. R correctly explains A.
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