Chromosome pairs line up across the equator of the spindle at metaphase I (5). In anaphase I the chromosomes separate and travel to opposite ends of the spindle. The chromosomes migrate to the equators of two new spindles for metaphase 2 (7). Next the chromatids are pulled apart in anaphase 2 to form four clusters of chromosomes in telophase 2. The nuclear envelopes reform around four haploid nuclei that will give rise gamete
Trisomy 21, also known as nondisjunction, means that there is an extra copy of chromosome 21 in the cell and is the most common. Translocation occurs when there are two 21 chromosomes plus an extra piece of chromosome 21 that had attached itself to another chromosome during the division process. Those who have mosaic down syndrome contain an extra chromosome 21 in only some of their cells while others are unaffected. People with mosaic down syndrome tend to have milder physical features and intellectual abilities than those who have trisomy 21 and translocation down syndrome. According to Mark Selikowitz, maternal age is a significant factor in causing trisomy 21. When females are born, all the eggs that a woman will produce are already present. The eggs wait years, some longer than others to be released and it is during the wait period (some 20-40 years) that it is believed errors can occur. On the contrary, man’s sperm does not remain standing therefore less probability for error. Additionally, people with a family history of down syndrome and people who carry the genetic translocation are factors to consider whether the child would be at
A) Meiosis consists of two cell divisions and is broken up into Meiosis I and Meiosis II. At the beginning of the Cell Cycle, in this case there are four chromatids each from the homologous pairs being A, a, B, b. This is the Diploid number (4) meaning it is 2 times the haploid number that will be seen at the end of meiosis II. During the S phase of interphase, the chromatids replicate and reach the end of G2 phase. Now starting meiosis, during the first stage of prophase I the chromosomes condense and pair up through synapsis with their sister chromatids creating AA, aa, BB, bb. After they pair up they go through a process called crossing over, where the homologous chromosomes share a piece of their genetic material with each other. Crossing over allows for the genetic diversity of chromosomes. Now there are four homologous chromosomes Aa, Aa, Bb, Bb, each containing heterozygous alleles because the sister chromatids exchanged genetic information with their homologous pair. During late prophase I, spindle fibers being to form where they will later attach to a homologous chromosomes centromere. The next stage is Metaphase I. During metaphase I, the homologous pairs line up at the metaphase plate, also known to be the center of the cell. The homologous pairs form a tetrad which is considered a group of four homologous chromosomes. These homologous chromosomes orient themselves randomly, which is know as the process of independent
Meiotic errors are alterations of a cell's chromosome number or structure. Chromosomal alterations happen in both mitosis and meiosis. But in other ways meiosis provides more opportunities for errors. Do to the three sources of genetic variation in meiosis that can also be opportunities for errors. Crossing over in prophase I independent assortment and in anaphase I and anaphase II are major sources of genetic variation in the sexually
The event in which a tetrad doesn’t split into homologous chromosomes or a homologous chromosome doesn’t split into sister chromatids, which causes an imbalance in the chromosome count of the produced gametes.
A con for sexual reproduction is during meiosis. An egg and sperm cell usually have 23 chromosomes each. When an egg gets fertilized by a sperm cell it combines to 46 chromosomes. Human beings have 46 chromosomes each. When something goes wrong and a baby inside a womb gets one more extra chromosome, they get Down syndrome.
The main problem with chromosome instability produced by these breaks is the susceptibility to translocations and thus oncogene activation.
discoveries is information regarding chromosomal and genetic disorders. Both chromosomal and genetic ailments can have harmful effects on the body. Genetic diseases such as Bloom's Syndrome occur as a result of gene alterations. These gene mutations cause the chromosomes to become unstable, leading to chromosomal breaks, separations and structural repositioning (Freivogel 170). Chromosomal diseases like Charcot-Marie Tooth Disease are also caused by mutations, which are nearly irreversible (Krajewski 232).
On September 12, 1016, Belmont University graciously allowed Dr. Katherine Friedman from Vanderbilt University to come and talk to a crowd of students about the tendencies of how deoxyribose double stranded breaks can during cell replication and the elements required to hopefully repair this ordeal. She began the session by discussing what chromosomes are composed of and how they are produced, accompanied by visual and statistical representations. Moving on, she touched on how double strand breaks are a huge threat to a cell's, an organisms, stability. Correspondingly, she described what can cause these breaks; chemical factors, as well as inner cell disruptions during replication that are sometimes hard to remedy. However, she also stated that this breaks can occur on purpose, mostly in the immune system in efforts to make antibodies.
A chromosomal disorder is caused by an abundance or reduction of genes on the chromosomes. This type of disorder may also be caused by structural changes within these chromosomes; this is known as an aneuploidy (Porth, 2015). The most common chromosomal disorder is Down syndrome of which there are three types: complete trisomy 21, translocation, and mosaicism (Porth, 2015). Since its first identification in 1866, researchers have become more knowledgeable about the etiology of Down syndrome. When one studies etiology, pathogenesis, and clinical manifestations of Down syndrome, he or she will begin to understand multiple chromosomal disorders.