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(e d18(a) What are chromosomes ? Where are they located in the cells ?(b)(c)What is a sex chromosome?Explain the mechanism of sex determination in human beings. |
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Answer» (a) Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique (b) Sex chromosomes are chromosomes which determine the sex of individual organisms. In man, for example, there are 23 pairs of chromosomes and one of these pairs are sex chromosomes. (c)In human beings, sex is determined by the sex chromosomes. Males have XY constitution of sex chromosomes. Females have XX constitution of sex chromosomes Sex of child depends on what happens during fertilization. i) If a sperm carrying X chromosome fertilizes an ovum which carries X chromosome, then the child born will be a girl.ii) If a sperm carrying Y chromosome fertilizes an ovum which carries X chromosome, then the child born will be a boy. |
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