Mitosis, Meiosis, Linked Genes, And Chromosomal Similarities

Mitosis, Meiosis, Linked Genes, and Chromosomal Abnormalities

Similarities between Mitosis and Meiosis

Both Mitosis and Meiosis are involved in the reproduction of eukaryotic cells in multicellular organisms. Both start from a diploid parent cell, where the process of cell nuclear division starts with one cell. The DNA of the primary cell is replicated once prior to nuclear partitioning. Meiosis and Mitosis are multistage processes, including an Interphase, a Prophase, a metaphase, an anaphase, and a telophase, or multiples thereof. Both go through a period of growth with the interphase, and genetic synthesis, before their cycles begin. DNA is replicated within the S, or synthesis, phase of Interphase. Mitosis is only similar to the Meiosis

Homologous chromosomes have the same genes, in the same order, at the same locations. Furthermore, they may not be identical as the alleles may differ. For example, although gene 1 is for eye colour, one codes for blue, the other for brown. In Meiosis, during Prophase I, once these chromosomes are subjected to synapsis, or pairing, during early meiosis, reciprocity arises, and the exchange of genetic material occurs resulting in a gene swap. It is the recombination nodules, located are various points along the synaptonemal protein structure, that define the spots (chiasmata) where the crossover will take place. Consequently, recombination rearranges, or reorganizes, chromosomes in such a way as to create new allele combinations, unless they are located too close together. This is crossing over is where we get our genetic diversity. However, linked genes throw the rules out the window and contravene Mendel's Law of Independent assortment, whereby, he states that dissimilar traits are inherited independently of the other. During the recombination, or crossing over, gene assignment does not change (OpenStax College,

One can see at a glance if there is something awry with the arrangement. The chromosome number is decreased, increased by duplication, or the amount of whole groupings of chromosomes is incorrect.

1. Nondisjunction – failure to divide of paired homologous chromosomes during Meiosis I or II

2. Aneuploidy – decrease (monosomy) or increase (trisomy) of chromosomes

45 or 47 rather than the normal 46

Decrease in the number of chromosomes

Increase in the number of chromosomes

The most common aneuploidic disorder is Trisomy 21, or Down Syndrome. This disorder is characterized by three chromosome 21s. See figure 4 for Trisomy 21 karyogram.

Common signs: Seen across all ethnic communities, a person with Down syndrome has short stature, distinct facies, short fingers & toes, broad hands, slanted eyes, thick tongue, and developmental delays.

3. Polyploidy – increased chromosome sets

Extremely rare, seen mostly among lizards, fish, amphibians

4. Sex chromosome nondisjunctions – X-inactivation

Example: Klinefelter Syndrome, one type XXY

Example: Turner Syndrome, usually characterized as X0

5. Duplications and Deletions – loss or duplication of a portion of the chromosome

Example: Cri-du-chat, deletion of