Mitosis or Meiosis?

Figure \(\PageIndex1\) shows a tiny embryo just start to form. When an egg is fertilized, the resulting single cell have to divide many times to build a fetus. Both mitosis and meiosis involve cabinet division; is this type of cell department an example of mitosis or meiosis? The answer is mitosis. With each division, you are making a genetically specific copy of the parent cell, which just happens v mitosis.

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Chromosome Disorders

Changes in Chromosome Number

What would happen if whole chromosome were missing or duplicated? What if a human had actually only 45 chromosomes? Or 47? This real possibility is usually as result of mistakes throughout meiosis; the chromosomes do not totally separate from each other throughout sperm or egg formation. Specifically, nondisjunction occurs as soon as homologous chromosomes or sister chromatids fail come separate throughout meiosis, causing an abnormal chromosome number. Nondisjunction might occur throughout meiosis ns or meiosis II Most human being atypical chromosome numbers result in the death of the occurring embryo, often before a woman also realizes she is pregnant. Occasionally, a zygote through an extra chromosome can come to be a viable embryo and develop.

Trisomy is a state wherein humans have an extra autosome. That is, they have three that a particular chromosome instead of two. For example, trisomy 18 outcomes from an extra chromosome 18, resulting in 47 total chromosomes. To identify the chromosome number (including one abnormal number), a sample of cells is removed from an individual or developing fetus. Metaphase chromosomes are photographed and also a karyotype is produced. A karyotype will display any kind of abnormalities in chromosome number or huge chromosomal rearrangements. Trisomy 8, 9, 12, 13, 16, 18, and 21 have been identified in humans. Trisomy 16 is the most common trisomy in humans, emerging in much more than 1% of pregnancies. This condition, however, usually results in spontaneous legacy in the first trimester. The most usual trisomy in viable births is Trisomy 21.

Figure \(\PageIndex3\): Nondisjunction in Meiosis: Nondisjunction occurs as soon as homologous chromosomes or sister chromatids fail to separate throughout meiosis, leading to an abnormal chromosome number. Nondisjunction may occur throughout meiosis ns or meiosis II. If nondisjunction wake up in meiosis I, the homologous pair that chromosomes stay bound. This results in one extra chromosome (n + 1) in 2 of the gametes and a lacking chromosome (n - 1) in two of the gametes. If nondisjunction wake up in meiosis II, two cells go into meiosis II through the correct variety of chromosomes. Nondisjunction wake up in one of these cells as soon as one that the sister chromatids does not separate. This results in a cell through an extra chromosome (n +1), a cell missing a chromosome (n - 1), and two cells through the expected variety of chromosomes (n).

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Figure \(\PageIndex5\): Trisomy 21 (Down Syndrome) Karyotype. A karyotype is a photo of a cell"s chromosomes. Keep in mind that there space two of every chromosome yet three duplicates of chromosome 21.

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