Organisms that undergo sexual reproduction need to make specialized cells in order for chromosomes to be passed on during fertilization. These cells, called gametes, are produced during a process called meiosis. Here, the sperm cell of the male and the ovum of the female are made from previously existing cells. After fertilization, the chromosomes combine in the new offspring to form an organism that has different genes from the parents. Having multiple offspring with genetic makeup different from their parents and each other increases the chances that at least one of those offspring survives in changing environments. Not all genetic variation is beneficial, however. Sometimes genes carry diseases that can have dramatic effects on the offspring.
At A Glance
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Sexually reproducing organisms produce gametes (sperm and egg).
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Chromosomes carry genes on them which are expressed as traits in the organism.
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Meiosis is the process of gamete (sex cell) formation.
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Genetic variation results from sexual reproduction, while asexual reproduction limits genetic variation and does not require meiosis.
- Several genetic disorders occur that can be passed on to offspring through the inheritance of chromosomes.
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Aneuploidy describes any condition in which an abnormal number of chromosomes is inherited. Polyploidy occurs when additional sets of chromosomes are inherited.
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Down syndrome results from three copies of chromosome 21 in humans, an example of trisomy.
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Turner's syndrome results from only a single sex chromosome rather than two, an example of monosomy.
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Klinefelter syndrome results from three sex chromosomes rather than two.
- Some genetic disorders are caused by errors during crossing-over, such that the organism has the correct number of chromosomes but the chromosomes themselves have been damaged.
