chromosomes-fertilization (1)

chromosomes-fertilization (1) - 1 Fertilization...

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Fertilization occurs when the nucleus of a male reproductive cell combines with the nucleus of a female reproductive cell The reproductive cells are called gametes In animals, the male gamete is the sperm cell and the female gamete is the ovum In flowering plants, the male gamete is a cell in the pollen grain and the female gamete is an egg cell in the ovule When the male and female gametes combine, the resulting cell is called a zygote 2 Fertilization
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pollen nucleus egg cell nuclei combine cell division (mitosis) embryo formed PLANT sperms ovum nuclei combine cell division (mitosis) embryo formed ANIMAL 3
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PLANT This sperm will fertilize the ovum 0.1 mm pollen grain the pollen cell reaches the egg cell through a pollen tube ovary egg cell ANIMAL 4 ovule
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As a result of fertilization, the chromosomes from the male and female cells are combined in the same nuclear membrane Do you see a problem with this? 5
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The problem is that if the full complement of male and female chromosomes combine, the zygote and embryo would have twice as many chromosomes as its parents If 46 male chromosomes combined with 46 female chromosomes, the offspring would have 92 chromosomes in their cells And the next generation would have 184 chromosomes, and so on In fact, when the gametes are formed, the number of chromosomes is halved so that the zygote ends up with the same number of chromosomes as its parents. 6
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is called At cell division, before the chromatids separate, the chromosomes are shared equally between the two daughter cells The following slides describe this process. Only two pairs of chromosomes are shown
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This note was uploaded on 11/29/2011 for the course BIO 218 taught by Professor Young during the Fall '11 term at BYU.

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chromosomes-fertilization (1) - 1 Fertilization...

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