Topic 4 2 doc
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Carly Topic 4.2 Summary: Meiosis Meiosis is a reduction division of diploid (somatic) cells into haploid gametes. The number of diploid chromosomes can be represented as 2n, and haploid as n. Meiosis is a process of two divisions. First, chromosomes replicate during the S-phase of interphone to make sister chromatids. Then, during Meiosis I, the homologous pairs are separated, and in Meiosis II the sister chromatids are separated. Homologous pairs are chromosomes with the same size and structures and with the same genes at the same loci. In meiosis, the pair is made up of one paternal and one maternal chromosome. When crossing over occurs in both divisions, the alleles on each corresponding gene are traded to create a unique chromosome; this precipitates genetic variation. The end product takes one somatic cell and reduces it to four haploid cells with half the number of chromosomes as the original. The Process of Meiosis Meiosis begins with interphase, in which chromosomes are replicated and cell processes are carried out. Homologous chromosomes pair up during prophase I, and crossing over occurs. In Metaphase I these pairs line up at the equator at the cell according to their bivalents, and then in Anaphase I these chromosomes are pulled apart to opposite poles. During telophase I, two nuclei form and cytokinesis splits the cytoplasm. The second round of division begins with prophase II, in which the nuclei break down. Next comes metaphase II, which is essentially the same process as metaphase I, in which the chromosomes line up at the equator of the cell. The chromosomes are pulled apart to opposite poles in anaphase II, and the individual haploid cells are created in telophase II. Non-Disjunction Non-Disjunction is an error that can occur during anaphase when the chromosomes are split, and the chromosomes are pulled to opposite poles unevenly. This creates the wrong number of chromosomes in the gamete. This creates flaws in the genetic makeup of an organism. For example, trisomy 21 is the non-disjunction that causes Down syndrome. Karyotyping
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Transcript of Topic 4 2 doc
Carly Topic 4.2 Summary: Meiosis
Meiosis is a reduction division of diploid (somatic) cells into haploid gametes. The number of diploid chromosomes can be represented as 2n, and haploid as n. Meiosis is a process of two divisions. First, chromosomes replicate during the S-phase of interphone to make sister chromatids. Then, during Meiosis I, the homologous pairs are separated, and in Meiosis II the sister chromatids are separated. Homologous pairs are chromosomes with the same size and structures and with the same genes at the same loci. In meiosis, the pair is made up of one paternal and one maternal chromosome. When crossing over occurs in both divisions, the alleles on each corresponding gene are traded to create a unique chromosome; this precipitates genetic variation. The end product takes one somatic cell and reduces it to four haploid cells with half the number of chromosomes as the original.
The Process of Meiosis
Meiosis begins with interphase, in which chromosomes are replicated and cell processes are carried out. Homologous chromosomes pair up during prophase I, and crossing over occurs. In Metaphase I these pairs line up at the equator at the cell according to their bivalents, and then in Anaphase I these chromosomes are pulled apart to opposite poles. During telophase I, two nuclei form and cytokinesis splits the cytoplasm. The second round of division begins with prophase II, in which the nuclei break down. Next comes metaphase II, which is essentially the same process as metaphase I, in which the chromosomes line up at the equator of the cell. The chromosomes are pulled apart to opposite poles in anaphase II, and the individual haploid cells are created in telophase II.
Non-Disjunction
Non-Disjunction is an error that can occur during anaphase when the chromosomes are split, and the chromosomes are pulled to opposite poles unevenly. This creates the wrong number of chromosomes in the gamete. This creates flaws in the genetic makeup of an organism. For example, trisomy 21 is the non-disjunction that causes Down syndrome.
Karyotyping
Karyotyping is a pre-natal test to test for gender and trisomy disorders. Chromosomes are taken by amniocentesis, and then they are arranged by shape and size, and finally a picture is taken. Gender can be determined by chromosome pair 1; if the pair is made up of two X chromosomes, then the embryo is female, and if the pair is made up of an X chromosome and a Y chromosome, then the embryo is male.
