L11 Week 1 Assignment

Meiosis consists of one DNA replication and two nuclear divisions resulting in 4 daughter cells. The process which provides for genetic variation is crossing over. Crossing over occurs in the early stages when homologous chromosomes move together so that their chromatids form a tetrad. This is called synapsis and allows for the exchange of chromosome sections.

2. a) How does meiosis introduce genetic variation into offspring? Think about how the chromosomes line up.(1 point)

Define the term crossing over. (3 points) During meiosis’ prophase the homologous chromatids exchange segments.

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

Turner Syndrome is a disorder that affects one in every two thousand girls. Usually girls are born with only one X chromosomes. Some are born with an extra chromosome, or sometimes even half of one is missing which causes Turner Syndrome.

This syndrome is from a mutation of a gene on chromosome 15 and this causes problems in the production of fibrillin-1 which is a protein that is an important part of connective tissue. The name for the gene is FBN1. Basically, it is the “glue” that helps to support the tissues in the human body. A child born to a parent with this syndrome has a 50% of having it. However, in the remaining 25%, neither parent has the disease which gives them a 1 in 10,000 chance of having a child with this disorder. When a child of two unaffected parents is born with it then the genetic mutation occurs in either the egg or sperm cell at the time of conception.

One out of five thousand children get Edwards or Trisomy 18 Syndrome and those children only live less than a few years. This negative mutation kills most babies after one year. It starts out all in the 18th Chromosome, which causes the disorder.

About 10% of all miscarriages have this disease to blame. Turner syndrome happens when a female’s X chromosome has both X’s in one cell, but not others (called Mosaic Turner Syndrome), or entirely missing (called Monosomy). It can also happen when instead of two X chromosomes, there’s one X and a small part of a Y chromosome. The girl will still develop as a female, however. All of these forms of Turner Syndrome can result in physical problems like heart or kidney defects, a shorter than normal stature, a failure to start puberty, and infertility, and mental problems like learning disabilities and social adjustment problems, to name just a few symptoms.

There are thousands of rare diseases known to mam kind that only affects one of every couple thousand people. Each of which have their own unique characteristics that define each disease from one another. The one disease that is closest to my last name is the Smith-Magenis Syndrome also known as (SMS). However, 1 in 25,000 are considered to have this condition but are currently not diagnosed with the disease. Although, many officials believe the number is closer to 1 in 15,000. Currently there have been no signs of this disease being inherited through genetics, this disease is caused by a deletion of a region of chromosomes. The Smith-Magenis Syndrome is a development disorder that has multiple effects on an infected person through physical appearances, speech and sleep disorders, and behavioral problems.

only 2, producing a total of 47 paired chromosomes instead of 46. This error usually happens during meiosis. In meiosis the division of cells happens and chromosomes are paired. The errors are random and there is no definitive or known cause of Down syndrome. Researchers learned that greater than 90% of all cases, the extra chromosome 21 copy comes from the mother’s egg, while approximately 4% comes from the sperm. The remaining cases the errors occur after the fertilization (National Institute of Health [NIH], 2014).

As a result, the missing chromosome can cause over 50 abnormalities that include: Anderman syndrome, Angelman syndrome, ataxia neuropathy spectrum, Bloom syndrome, breast cancer, Marfan syndrome, Prada-Willis syndrome, Tay-Sachs disease, and a lot more, depending on which gene is affected. Generally, the most common observable behaviors are: intellectual disability, seizures, psychiatric disorders, distinctive facial features and moodiness. Of particular interest is Angelman syndrome which is also a sex-linked disorder. But regardless of the source of inheritance, this disorder can be observed as any of the above listed behaviors or medical

and type 0 (prenatal). With an incidence of 1 in 10,000 births, it is anautosomal recessive disorder associated with severe neuromuscularweakness and premature death in the majority of

A commonly asked question for all genetic disorders is “Who get’s it”? The answer is simple. Anyone can be born with 5p syndrome. 5p syndrome is not more prominent in any group of people. Since it is a random event that happens in the fetal development it can happen in all cultures, genders, and ethnicities. It happens in every 1 in 20,000 to 50,000 newborns and isn’t very common.

Uniparental disomy is when both members of a chromosome pair comes from one parent, while the chromosome from the other parent is lost. During anaphase in meiosis II, the chromosomes fail to split properly, which will cause two abnormal daughter cells. This is termed the anaphase lag where a gamete will end up with 47 chromosomes instead of 46 (Shaffer et al. 2001). Usually what will happen during meiosis is that one diploid cell will form two haploid daughter cells, and then those two daughter cells will form two more haploid daughter cells. This makes four haploid daughter cells at the end of meiosis. Sometimes a mutation will occur where a daughter cell produced in meiosis will have either three copies or one single copy of a chromosome

Independent assortment occurs during meiosis when both maternal and paternal homologous pairs separate independently, distributing chromatids from each parent to the gametes independent of each other (Mendel, 1865). As maternal and paternal chromosomes carry different genetic information, independent assortment produces different possible combinations of chromosome pairs. Recombination is a feature of independent assortment, producing further new gene combinations by breaking and recombining DNA fragments. Following this is crossing over; the exchange of genetic material during meiosis between non sister